2019-06-04 16:11:33 +08:00
|
|
|
/* SPDX-License-Identifier: GPL-2.0-only */
|
2014-04-30 17:54:33 +08:00
|
|
|
/*
|
|
|
|
|
* arch/arm64/kernel/entry-ftrace.S
|
|
|
|
|
*
|
|
|
|
|
* Copyright (C) 2013 Linaro Limited
|
|
|
|
|
* Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
|
|
|
|
|
*/
|
|
|
|
|
|
|
|
|
|
#include <linux/linkage.h>
|
2022-10-18 19:49:21 +08:00
|
|
|
#include <linux/cfi_types.h>
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
#include <asm/asm-offsets.h>
|
2017-02-15 05:32:58 +08:00
|
|
|
#include <asm/assembler.h>
|
2014-04-30 17:54:33 +08:00
|
|
|
#include <asm/ftrace.h>
|
|
|
|
|
#include <asm/insn.h>
|
|
|
|
|
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
/*
|
|
|
|
|
* Due to -fpatchable-function-entry=2, the compiler has placed two NOPs before
|
|
|
|
|
* the regular function prologue. For an enabled callsite, ftrace_init_nop() and
|
|
|
|
|
* ftrace_make_call() have patched those NOPs to:
|
|
|
|
|
*
|
|
|
|
|
* MOV X9, LR
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
* BL ftrace_caller
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
*
|
2020-05-18 21:01:01 +08:00
|
|
|
* Each instrumented function follows the AAPCS, so here x0-x8 and x18-x30 are
|
|
|
|
|
* live (x18 holds the Shadow Call Stack pointer), and x9-x17 are safe to
|
|
|
|
|
* clobber.
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
*
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
* We save the callsite's context into a struct ftrace_regs before invoking any
|
|
|
|
|
* ftrace callbacks. So that we can get a sensible backtrace, we create frame
|
|
|
|
|
* records for the callsite and the ftrace entry assembly. This is not
|
|
|
|
|
* sufficient for reliable stacktrace: until we create the callsite stack
|
|
|
|
|
* record, its caller is missing from the LR and existing chain of frame
|
|
|
|
|
* records.
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
*/
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
SYM_CODE_START(ftrace_caller)
|
|
|
|
|
bti c
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
/* Save original SP */
|
|
|
|
|
mov x10, sp
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
/* Make room for ftrace regs, plus two frame records */
|
|
|
|
|
sub sp, sp, #(FREGS_SIZE + 32)
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
/* Save function arguments */
|
|
|
|
|
stp x0, x1, [sp, #FREGS_X0]
|
|
|
|
|
stp x2, x3, [sp, #FREGS_X2]
|
|
|
|
|
stp x4, x5, [sp, #FREGS_X4]
|
|
|
|
|
stp x6, x7, [sp, #FREGS_X6]
|
|
|
|
|
str x8, [sp, #FREGS_X8]
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
/* Save the callsite's FP, LR, SP */
|
|
|
|
|
str x29, [sp, #FREGS_FP]
|
|
|
|
|
str x9, [sp, #FREGS_LR]
|
|
|
|
|
str x10, [sp, #FREGS_SP]
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
/* Save the PC after the ftrace callsite */
|
|
|
|
|
str x30, [sp, #FREGS_PC]
|
|
|
|
|
|
|
|
|
|
/* Create a frame record for the callsite above the ftrace regs */
|
|
|
|
|
stp x29, x9, [sp, #FREGS_SIZE + 16]
|
|
|
|
|
add x29, sp, #FREGS_SIZE + 16
|
|
|
|
|
|
|
|
|
|
/* Create our frame record above the ftrace regs */
|
|
|
|
|
stp x29, x30, [sp, #FREGS_SIZE]
|
|
|
|
|
add x29, sp, #FREGS_SIZE
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
arm64: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS
This patch enables support for DYNAMIC_FTRACE_WITH_CALL_OPS on arm64.
This allows each ftrace callsite to provide an ftrace_ops to the common
ftrace trampoline, allowing each callsite to invoke distinct tracer
functions without the need to fall back to list processing or to
allocate custom trampolines for each callsite. This significantly speeds
up cases where multiple distinct trace functions are used and callsites
are mostly traced by a single tracer.
The main idea is to place a pointer to the ftrace_ops as a literal at a
fixed offset from the function entry point, which can be recovered by
the common ftrace trampoline. Using a 64-bit literal avoids branch range
limitations, and permits the ops to be swapped atomically without
special considerations that apply to code-patching. In future this will
also allow for the implementation of DYNAMIC_FTRACE_WITH_DIRECT_CALLS
without branch range limitations by using additional fields in struct
ftrace_ops.
As noted in the core patch adding support for
DYNAMIC_FTRACE_WITH_CALL_OPS, this approach allows for directly invoking
ftrace_ops::func even for ftrace_ops which are dynamically-allocated (or
part of a module), without going via ftrace_ops_list_func.
Currently, this approach is not compatible with CLANG_CFI, as the
presence/absence of pre-function NOPs changes the offset of the
pre-function type hash, and there's no existing mechanism to ensure a
consistent offset for instrumented and uninstrumented functions. When
CLANG_CFI is enabled, the existing scheme with a global ops->func
pointer is used, and there should be no functional change. I am
currently working with others to allow the two to work together in
future (though this will liekly require updated compiler support).
I've benchamrked this with the ftrace_ops sample module [1], which is
not currently upstream, but available at:
https://lore.kernel.org/lkml/20230103124912.2948963-1-mark.rutland@arm.com
git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git ftrace-ops-sample-20230109
Using that module I measured the total time taken for 100,000 calls to a
trivial instrumented function, with a number of tracers enabled with
relevant filters (which would apply to the instrumented function) and a
number of tracers enabled with irrelevant filters (which would not apply
to the instrumented function). I tested on an M1 MacBook Pro, running
under a HVF-accelerated QEMU VM (i.e. on real hardware).
Before this patch:
Number of tracers || Total time | Per-call average time (ns)
Relevant | Irrelevant || (ns) | Total | Overhead
=========+============++=============+==============+============
0 | 0 || 94,583 | 0.95 | -
0 | 1 || 93,709 | 0.94 | -
0 | 2 || 93,666 | 0.94 | -
0 | 10 || 93,709 | 0.94 | -
0 | 100 || 93,792 | 0.94 | -
---------+------------++-------------+--------------+------------
1 | 1 || 6,467,833 | 64.68 | 63.73
1 | 2 || 7,509,708 | 75.10 | 74.15
1 | 10 || 23,786,792 | 237.87 | 236.92
1 | 100 || 106,432,500 | 1,064.43 | 1063.38
---------+------------++-------------+--------------+------------
1 | 0 || 1,431,875 | 14.32 | 13.37
2 | 0 || 6,456,334 | 64.56 | 63.62
10 | 0 || 22,717,000 | 227.17 | 226.22
100 | 0 || 103,293,667 | 1032.94 | 1031.99
---------+------------++-------------+--------------+--------------
Note: per-call overhead is estimated relative to the baseline case
with 0 relevant tracers and 0 irrelevant tracers.
After this patch
Number of tracers || Total time | Per-call average time (ns)
Relevant | Irrelevant || (ns) | Total | Overhead
=========+============++=============+==============+============
0 | 0 || 94,541 | 0.95 | -
0 | 1 || 93,666 | 0.94 | -
0 | 2 || 93,709 | 0.94 | -
0 | 10 || 93,667 | 0.94 | -
0 | 100 || 93,792 | 0.94 | -
---------+------------++-------------+--------------+------------
1 | 1 || 281,000 | 2.81 | 1.86
1 | 2 || 281,042 | 2.81 | 1.87
1 | 10 || 280,958 | 2.81 | 1.86
1 | 100 || 281,250 | 2.81 | 1.87
---------+------------++-------------+--------------+------------
1 | 0 || 280,959 | 2.81 | 1.86
2 | 0 || 6,502,708 | 65.03 | 64.08
10 | 0 || 18,681,209 | 186.81 | 185.87
100 | 0 || 103,550,458 | 1,035.50 | 1034.56
---------+------------++-------------+--------------+------------
Note: per-call overhead is estimated relative to the baseline case
with 0 relevant tracers and 0 irrelevant tracers.
As can be seen from the above:
a) Whenever there is a single relevant tracer function associated with a
tracee, the overhead of invoking the tracer is constant, and does not
scale with the number of tracers which are *not* associated with that
tracee.
b) The overhead for a single relevant tracer has dropped to ~1/7 of the
overhead prior to this series (from 13.37ns to 1.86ns). This is
largely due to permitting calls to dynamically-allocated ftrace_ops
without going through ftrace_ops_list_func.
I've run the ftrace selftests from v6.2-rc3, which reports:
| # of passed: 110
| # of failed: 0
| # of unresolved: 3
| # of untested: 0
| # of unsupported: 0
| # of xfailed: 1
| # of undefined(test bug): 0
... where the unresolved entries were the tests for DIRECT functions
(which are not supported), and the checkbashisms selftest (which is
irrelevant here):
| [8] Test ftrace direct functions against tracers [UNRESOLVED]
| [9] Test ftrace direct functions against kprobes [UNRESOLVED]
| [62] Meta-selftest: Checkbashisms [UNRESOLVED]
... with all other tests passing (or failing as expected).
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230123134603.1064407-9-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2023-01-23 21:46:03 +08:00
|
|
|
/* Prepare arguments for the the tracer func */
|
|
|
|
|
sub x0, x30, #AARCH64_INSN_SIZE // ip (callsite's BL insn)
|
|
|
|
|
mov x1, x9 // parent_ip (callsite's LR)
|
|
|
|
|
mov x3, sp // regs
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
|
|
|
|
|
/*
|
|
|
|
|
* The literal pointer to the ops is at an 8-byte aligned boundary
|
|
|
|
|
* which is either 12 or 16 bytes before the BL instruction in the call
|
|
|
|
|
* site. See ftrace_call_adjust() for details.
|
|
|
|
|
*
|
|
|
|
|
* Therefore here the LR points at `literal + 16` or `literal + 20`,
|
|
|
|
|
* and we can find the address of the literal in either case by
|
|
|
|
|
* aligning to an 8-byte boundary and subtracting 16. We do the
|
|
|
|
|
* alignment first as this allows us to fold the subtraction into the
|
|
|
|
|
* LDR.
|
|
|
|
|
*/
|
|
|
|
|
bic x2, x30, 0x7
|
|
|
|
|
ldr x2, [x2, #-16] // op
|
|
|
|
|
|
|
|
|
|
ldr x4, [x2, #FTRACE_OPS_FUNC] // op->func
|
|
|
|
|
blr x4 // op->func(ip, parent_ip, op, regs)
|
|
|
|
|
|
|
|
|
|
#else
|
|
|
|
|
ldr_l x2, function_trace_op // op
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
|
arm64: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS
This patch enables support for DYNAMIC_FTRACE_WITH_CALL_OPS on arm64.
This allows each ftrace callsite to provide an ftrace_ops to the common
ftrace trampoline, allowing each callsite to invoke distinct tracer
functions without the need to fall back to list processing or to
allocate custom trampolines for each callsite. This significantly speeds
up cases where multiple distinct trace functions are used and callsites
are mostly traced by a single tracer.
The main idea is to place a pointer to the ftrace_ops as a literal at a
fixed offset from the function entry point, which can be recovered by
the common ftrace trampoline. Using a 64-bit literal avoids branch range
limitations, and permits the ops to be swapped atomically without
special considerations that apply to code-patching. In future this will
also allow for the implementation of DYNAMIC_FTRACE_WITH_DIRECT_CALLS
without branch range limitations by using additional fields in struct
ftrace_ops.
As noted in the core patch adding support for
DYNAMIC_FTRACE_WITH_CALL_OPS, this approach allows for directly invoking
ftrace_ops::func even for ftrace_ops which are dynamically-allocated (or
part of a module), without going via ftrace_ops_list_func.
Currently, this approach is not compatible with CLANG_CFI, as the
presence/absence of pre-function NOPs changes the offset of the
pre-function type hash, and there's no existing mechanism to ensure a
consistent offset for instrumented and uninstrumented functions. When
CLANG_CFI is enabled, the existing scheme with a global ops->func
pointer is used, and there should be no functional change. I am
currently working with others to allow the two to work together in
future (though this will liekly require updated compiler support).
I've benchamrked this with the ftrace_ops sample module [1], which is
not currently upstream, but available at:
https://lore.kernel.org/lkml/20230103124912.2948963-1-mark.rutland@arm.com
git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git ftrace-ops-sample-20230109
Using that module I measured the total time taken for 100,000 calls to a
trivial instrumented function, with a number of tracers enabled with
relevant filters (which would apply to the instrumented function) and a
number of tracers enabled with irrelevant filters (which would not apply
to the instrumented function). I tested on an M1 MacBook Pro, running
under a HVF-accelerated QEMU VM (i.e. on real hardware).
Before this patch:
Number of tracers || Total time | Per-call average time (ns)
Relevant | Irrelevant || (ns) | Total | Overhead
=========+============++=============+==============+============
0 | 0 || 94,583 | 0.95 | -
0 | 1 || 93,709 | 0.94 | -
0 | 2 || 93,666 | 0.94 | -
0 | 10 || 93,709 | 0.94 | -
0 | 100 || 93,792 | 0.94 | -
---------+------------++-------------+--------------+------------
1 | 1 || 6,467,833 | 64.68 | 63.73
1 | 2 || 7,509,708 | 75.10 | 74.15
1 | 10 || 23,786,792 | 237.87 | 236.92
1 | 100 || 106,432,500 | 1,064.43 | 1063.38
---------+------------++-------------+--------------+------------
1 | 0 || 1,431,875 | 14.32 | 13.37
2 | 0 || 6,456,334 | 64.56 | 63.62
10 | 0 || 22,717,000 | 227.17 | 226.22
100 | 0 || 103,293,667 | 1032.94 | 1031.99
---------+------------++-------------+--------------+--------------
Note: per-call overhead is estimated relative to the baseline case
with 0 relevant tracers and 0 irrelevant tracers.
After this patch
Number of tracers || Total time | Per-call average time (ns)
Relevant | Irrelevant || (ns) | Total | Overhead
=========+============++=============+==============+============
0 | 0 || 94,541 | 0.95 | -
0 | 1 || 93,666 | 0.94 | -
0 | 2 || 93,709 | 0.94 | -
0 | 10 || 93,667 | 0.94 | -
0 | 100 || 93,792 | 0.94 | -
---------+------------++-------------+--------------+------------
1 | 1 || 281,000 | 2.81 | 1.86
1 | 2 || 281,042 | 2.81 | 1.87
1 | 10 || 280,958 | 2.81 | 1.86
1 | 100 || 281,250 | 2.81 | 1.87
---------+------------++-------------+--------------+------------
1 | 0 || 280,959 | 2.81 | 1.86
2 | 0 || 6,502,708 | 65.03 | 64.08
10 | 0 || 18,681,209 | 186.81 | 185.87
100 | 0 || 103,550,458 | 1,035.50 | 1034.56
---------+------------++-------------+--------------+------------
Note: per-call overhead is estimated relative to the baseline case
with 0 relevant tracers and 0 irrelevant tracers.
As can be seen from the above:
a) Whenever there is a single relevant tracer function associated with a
tracee, the overhead of invoking the tracer is constant, and does not
scale with the number of tracers which are *not* associated with that
tracee.
b) The overhead for a single relevant tracer has dropped to ~1/7 of the
overhead prior to this series (from 13.37ns to 1.86ns). This is
largely due to permitting calls to dynamically-allocated ftrace_ops
without going through ftrace_ops_list_func.
I've run the ftrace selftests from v6.2-rc3, which reports:
| # of passed: 110
| # of failed: 0
| # of unresolved: 3
| # of untested: 0
| # of unsupported: 0
| # of xfailed: 1
| # of undefined(test bug): 0
... where the unresolved entries were the tests for DIRECT functions
(which are not supported), and the checkbashisms selftest (which is
irrelevant here):
| [8] Test ftrace direct functions against tracers [UNRESOLVED]
| [9] Test ftrace direct functions against kprobes [UNRESOLVED]
| [62] Meta-selftest: Checkbashisms [UNRESOLVED]
... with all other tests passing (or failing as expected).
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230123134603.1064407-9-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2023-01-23 21:46:03 +08:00
|
|
|
bl ftrace_stub // func(ip, parent_ip, op, regs)
|
|
|
|
|
#endif
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
|
|
|
|
|
* x19-x29 per the AAPCS, and we created frame records upon entry, so we need
|
|
|
|
|
* to restore x0-x8, x29, and x30.
|
|
|
|
|
*/
|
|
|
|
|
/* Restore function arguments */
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
ldp x0, x1, [sp, #FREGS_X0]
|
|
|
|
|
ldp x2, x3, [sp, #FREGS_X2]
|
|
|
|
|
ldp x4, x5, [sp, #FREGS_X4]
|
|
|
|
|
ldp x6, x7, [sp, #FREGS_X6]
|
|
|
|
|
ldr x8, [sp, #FREGS_X8]
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
|
|
|
|
/* Restore the callsite's FP, LR, PC */
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
ldr x29, [sp, #FREGS_FP]
|
|
|
|
|
ldr x30, [sp, #FREGS_LR]
|
|
|
|
|
ldr x9, [sp, #FREGS_PC]
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
|
|
|
|
/* Restore the callsite's SP */
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
add sp, sp, #FREGS_SIZE + 32
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
|
|
|
|
ret x9
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
SYM_CODE_END(ftrace_caller)
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
#else /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
2014-04-30 17:54:33 +08:00
|
|
|
/*
|
|
|
|
|
* Gcc with -pg will put the following code in the beginning of each function:
|
|
|
|
|
* mov x0, x30
|
|
|
|
|
* bl _mcount
|
|
|
|
|
* [function's body ...]
|
|
|
|
|
* "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
|
|
|
|
|
* ftrace is enabled.
|
|
|
|
|
*
|
|
|
|
|
* Please note that x0 as an argument will not be used here because we can
|
|
|
|
|
* get lr(x30) of instrumented function at any time by winding up call stack
|
|
|
|
|
* as long as the kernel is compiled without -fomit-frame-pointer.
|
|
|
|
|
* (or CONFIG_FRAME_POINTER, this is forced on arm64)
|
|
|
|
|
*
|
|
|
|
|
* stack layout after mcount_enter in _mcount():
|
|
|
|
|
*
|
|
|
|
|
* current sp/fp => 0:+-----+
|
|
|
|
|
* in _mcount() | x29 | -> instrumented function's fp
|
|
|
|
|
* +-----+
|
|
|
|
|
* | x30 | -> _mcount()'s lr (= instrumented function's pc)
|
|
|
|
|
* old sp => +16:+-----+
|
|
|
|
|
* when instrumented | |
|
|
|
|
|
* function calls | ... |
|
|
|
|
|
* _mcount() | |
|
|
|
|
|
* | |
|
|
|
|
|
* instrumented => +xx:+-----+
|
|
|
|
|
* function's fp | x29 | -> parent's fp
|
|
|
|
|
* +-----+
|
|
|
|
|
* | x30 | -> instrumented function's lr (= parent's pc)
|
|
|
|
|
* +-----+
|
|
|
|
|
* | ... |
|
|
|
|
|
*/
|
|
|
|
|
|
|
|
|
|
.macro mcount_enter
|
|
|
|
|
stp x29, x30, [sp, #-16]!
|
|
|
|
|
mov x29, sp
|
|
|
|
|
.endm
|
|
|
|
|
|
|
|
|
|
.macro mcount_exit
|
|
|
|
|
ldp x29, x30, [sp], #16
|
|
|
|
|
ret
|
|
|
|
|
.endm
|
|
|
|
|
|
|
|
|
|
.macro mcount_adjust_addr rd, rn
|
|
|
|
|
sub \rd, \rn, #AARCH64_INSN_SIZE
|
|
|
|
|
.endm
|
|
|
|
|
|
|
|
|
|
/* for instrumented function's parent */
|
|
|
|
|
.macro mcount_get_parent_fp reg
|
|
|
|
|
ldr \reg, [x29]
|
|
|
|
|
ldr \reg, [\reg]
|
|
|
|
|
.endm
|
|
|
|
|
|
|
|
|
|
/* for instrumented function */
|
|
|
|
|
.macro mcount_get_pc0 reg
|
|
|
|
|
mcount_adjust_addr \reg, x30
|
|
|
|
|
.endm
|
|
|
|
|
|
|
|
|
|
.macro mcount_get_pc reg
|
|
|
|
|
ldr \reg, [x29, #8]
|
|
|
|
|
mcount_adjust_addr \reg, \reg
|
|
|
|
|
.endm
|
|
|
|
|
|
|
|
|
|
.macro mcount_get_lr reg
|
|
|
|
|
ldr \reg, [x29]
|
|
|
|
|
ldr \reg, [\reg, #8]
|
|
|
|
|
.endm
|
|
|
|
|
|
|
|
|
|
.macro mcount_get_lr_addr reg
|
|
|
|
|
ldr \reg, [x29]
|
|
|
|
|
add \reg, \reg, #8
|
|
|
|
|
.endm
|
|
|
|
|
|
2014-04-30 17:54:34 +08:00
|
|
|
/*
|
|
|
|
|
* _mcount() is used to build the kernel with -pg option, but all the branch
|
|
|
|
|
* instructions to _mcount() are replaced to NOP initially at kernel start up,
|
|
|
|
|
* and later on, NOP to branch to ftrace_caller() when enabled or branch to
|
|
|
|
|
* NOP when disabled per-function base.
|
|
|
|
|
*/
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_FUNC_START(_mcount)
|
2014-04-30 17:54:34 +08:00
|
|
|
ret
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_FUNC_END(_mcount)
|
2018-12-08 02:08:22 +08:00
|
|
|
EXPORT_SYMBOL(_mcount)
|
|
|
|
|
NOKPROBE(_mcount)
|
2014-04-30 17:54:34 +08:00
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* void ftrace_caller(unsigned long return_address)
|
|
|
|
|
* @return_address: return address to instrumented function
|
|
|
|
|
*
|
|
|
|
|
* This function is a counterpart of _mcount() in 'static' ftrace, and
|
|
|
|
|
* makes calls to:
|
|
|
|
|
* - tracer function to probe instrumented function's entry,
|
|
|
|
|
* - ftrace_graph_caller to set up an exit hook
|
|
|
|
|
*/
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_FUNC_START(ftrace_caller)
|
2014-04-30 17:54:34 +08:00
|
|
|
mcount_enter
|
|
|
|
|
|
|
|
|
|
mcount_get_pc0 x0 // function's pc
|
|
|
|
|
mcount_get_lr x1 // function's lr
|
|
|
|
|
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) // tracer(pc, lr);
|
2014-04-30 17:54:34 +08:00
|
|
|
nop // This will be replaced with "bl xxx"
|
|
|
|
|
// where xxx can be any kind of tracer.
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
|
2020-03-11 10:36:53 +08:00
|
|
|
SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
|
2014-04-30 17:54:34 +08:00
|
|
|
nop // If enabled, this will be replaced
|
|
|
|
|
// "b ftrace_graph_caller"
|
|
|
|
|
#endif
|
|
|
|
|
|
|
|
|
|
mcount_exit
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_FUNC_END(ftrace_caller)
|
2014-04-30 17:54:33 +08:00
|
|
|
|
|
|
|
|
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
|
|
|
|
|
/*
|
|
|
|
|
* void ftrace_graph_caller(void)
|
|
|
|
|
*
|
|
|
|
|
* Called from _mcount() or ftrace_caller() when function_graph tracer is
|
|
|
|
|
* selected.
|
|
|
|
|
* This function w/ prepare_ftrace_return() fakes link register's value on
|
|
|
|
|
* the call stack in order to intercept instrumented function's return path
|
|
|
|
|
* and run return_to_handler() later on its exit.
|
|
|
|
|
*/
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_FUNC_START(ftrace_graph_caller)
|
2018-11-16 06:42:03 +08:00
|
|
|
mcount_get_pc x0 // function's pc
|
|
|
|
|
mcount_get_lr_addr x1 // pointer to function's saved lr
|
2014-04-30 17:54:33 +08:00
|
|
|
mcount_get_parent_fp x2 // parent's fp
|
2018-11-16 06:42:03 +08:00
|
|
|
bl prepare_ftrace_return // prepare_ftrace_return(pc, &lr, fp)
|
2014-04-30 17:54:33 +08:00
|
|
|
|
|
|
|
|
mcount_exit
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_FUNC_END(ftrace_graph_caller)
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
|
ftrace: arm64: move from REGS to ARGS
This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).
FTRACE_WITH_REGS has been supported on arm64 since commit:
3b23e4991fb66f6d ("arm64: implement ftrace with regs")
As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:
(1) To make it possible to use the ftrace graph tracer with pointer
authentication, where it's necessary to snapshot/manipulate the LR
before it is signed by the instrumented function.
(2) To make it possible to implement LIVEPATCH in future, where we need
to hook function entry before an instrumented function manipulates
the stack or argument registers. Practically speaking, we need to
preserve the argument/return registers, PC, LR, and SP.
Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:
https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
Per AAPCS64, all function call argument and return values are held in
the following GPRs:
* X0 - X7 : parameter / result registers
* X8 : indirect result location register
* SP : stack pointer (AKA SP)
Additionally, ad function call boundaries, the following GPRs hold
context/return information:
* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)
... and for ftrace we need to capture the instrumented address:
* PC : program counter
No other GPRs are relevant, as none of the other arguments hold
parameters or return values:
* X9 - X17 : temporaries, may be clobbered
* X18 : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved
This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.
This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.
As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.
I've tested this with the ftrace selftests, where there are no
unexpected failures.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2022-11-04 01:05:20 +08:00
|
|
|
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
|
2022-10-18 19:49:21 +08:00
|
|
|
SYM_TYPED_FUNC_START(ftrace_stub)
|
arm64: implement ftrace with regs
This patch implements FTRACE_WITH_REGS for arm64, which allows a traced
function's arguments (and some other registers) to be captured into a
struct pt_regs, allowing these to be inspected and/or modified. This is
a building block for live-patching, where a function's arguments may be
forwarded to another function. This is also necessary to enable ftrace
and in-kernel pointer authentication at the same time, as it allows the
LR value to be captured and adjusted prior to signing.
Using GCC's -fpatchable-function-entry=N option, we can have the
compiler insert a configurable number of NOPs between the function entry
point and the usual prologue. This also ensures functions are AAPCS
compliant (e.g. disabling inter-procedural register allocation).
For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the
following:
| unsigned long bar(void);
|
| unsigned long foo(void)
| {
| return bar() + 1;
| }
... to:
| <foo>:
| nop
| nop
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl 0 <bar>
| add x0, x0, #0x1
| ldp x29, x30, [sp], #16
| ret
This patch builds the kernel with -fpatchable-function-entry=2,
prefixing each function with two NOPs. To trace a function, we replace
these NOPs with a sequence that saves the LR into a GPR, then calls an
ftrace entry assembly function which saves this and other relevant
registers:
| mov x9, x30
| bl <ftrace-entry>
Since patchable functions are AAPCS compliant (and the kernel does not
use x18 as a platform register), x9-x18 can be safely clobbered in the
patched sequence and the ftrace entry code.
There are now two ftrace entry functions, ftrace_regs_entry (which saves
all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is
allocated for each within modules.
Signed-off-by: Torsten Duwe <duwe@suse.de>
[Mark: rework asm, comments, PLTs, initialization, commit message]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Will Deacon <will@kernel.org>
2019-02-08 23:10:19 +08:00
|
|
|
ret
|
2020-02-19 03:58:30 +08:00
|
|
|
SYM_FUNC_END(ftrace_stub)
|
2014-04-30 17:54:33 +08:00
|
|
|
|
2022-11-10 03:28:31 +08:00
|
|
|
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
|
2022-10-18 19:49:21 +08:00
|
|
|
SYM_TYPED_FUNC_START(ftrace_stub_graph)
|
|
|
|
|
ret
|
|
|
|
|
SYM_FUNC_END(ftrace_stub_graph)
|
|
|
|
|
|
2014-04-30 17:54:33 +08:00
|
|
|
/*
|
|
|
|
|
* void return_to_handler(void)
|
|
|
|
|
*
|
|
|
|
|
* Run ftrace_return_to_handler() before going back to parent.
|
2018-11-16 06:42:00 +08:00
|
|
|
* @fp is checked against the value passed by ftrace_graph_caller().
|
2014-04-30 17:54:33 +08:00
|
|
|
*/
|
2020-02-19 03:58:32 +08:00
|
|
|
SYM_CODE_START(return_to_handler)
|
2018-11-16 06:42:02 +08:00
|
|
|
/* save return value regs */
|
|
|
|
|
sub sp, sp, #64
|
|
|
|
|
stp x0, x1, [sp]
|
|
|
|
|
stp x2, x3, [sp, #16]
|
|
|
|
|
stp x4, x5, [sp, #32]
|
|
|
|
|
stp x6, x7, [sp, #48]
|
|
|
|
|
|
2014-04-30 17:54:33 +08:00
|
|
|
mov x0, x29 // parent's fp
|
|
|
|
|
bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
|
|
|
|
|
mov x30, x0 // restore the original return address
|
2018-11-16 06:42:02 +08:00
|
|
|
|
|
|
|
|
/* restore return value regs */
|
|
|
|
|
ldp x0, x1, [sp]
|
|
|
|
|
ldp x2, x3, [sp, #16]
|
|
|
|
|
ldp x4, x5, [sp, #32]
|
|
|
|
|
ldp x6, x7, [sp, #48]
|
|
|
|
|
add sp, sp, #64
|
|
|
|
|
|
2014-04-30 17:54:33 +08:00
|
|
|
ret
|
2020-02-19 03:58:32 +08:00
|
|
|
SYM_CODE_END(return_to_handler)
|
2014-04-30 17:54:33 +08:00
|
|
|
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
|