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x86/entry/unwind: Create stack frames for saved interrupt registers 

With frame pointers, when a task is interrupted, its stack is no longer
completely reliable because the function could have been interrupted
before it had a chance to save the previous frame pointer on the stack.
So the caller of the interrupted function could get skipped by a stack
trace.

This is problematic for live patching, which needs to know whether a
stack trace of a sleeping task can be relied upon.  There's currently no
way to detect if a sleeping task was interrupted by a page fault
exception or preemption before it went to sleep.

Another issue is that when dumping the stack of an interrupted task, the
unwinder has no way of knowing where the saved pt_regs registers are, so
it can't print them.

This solves those issues by encoding the pt_regs pointer in the frame
pointer on entry from an interrupt or an exception.

This patch also updates the unwinder to be able to decode it, because
otherwise the unwinder would be broken by this change.

Note that this causes a change in the behavior of the unwinder: each
instance of a pt_regs on the stack is now considered a "frame".  So
callers of unwind_get_return_address() will now get an occasional
'regs->ip' address that would have previously been skipped over.

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/8b9f84a21e39d249049e0547b559ff8da0df0988.1476973742.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Josh Poimboeuf 2016-10-20 11:34:40 -05:00 committed by Ingo Molnar
parent 29a6d7964d
commit 946c191161
5 changed files with 139 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
arch/x86/entry/calling.h
View File

@ -192,6 +192,26 @@ For 32-bit we have the following conventions - kernel is built with
.byte 0xf1
.endm
/*
* This is a sneaky trick to help the unwinder find pt_regs on the stack. The
* frame pointer is replaced with an encoded pointer to pt_regs. The encoding
* is just setting the LSB, which makes it an invalid stack address and is also
* a signal to the unwinder that it's a pt_regs pointer in disguise.
*
* NOTE: This macro must be used *after* SAVE_EXTRA_REGS because it corrupts
* the original rbp.
*/
.macro ENCODE_FRAME_POINTER ptregs_offset=0
#ifdef CONFIG_FRAME_POINTER
.if \ptregs_offset
leaq \ptregs_offset(%rsp), %rbp
.else
mov %rsp, %rbp
.endif
orq $0x1, %rbp
#endif
.endm
#endif /* CONFIG_X86_64 */
/*

33
arch/x86/entry/entry_32.S
View File

@ -176,6 +176,22 @@
SET_KERNEL_GS %edx
.endm
/*
* This is a sneaky trick to help the unwinder find pt_regs on the stack. The
* frame pointer is replaced with an encoded pointer to pt_regs. The encoding
* is just setting the LSB, which makes it an invalid stack address and is also
* a signal to the unwinder that it's a pt_regs pointer in disguise.
*
* NOTE: This macro must be used *after* SAVE_ALL because it corrupts the
* original rbp.
*/
.macro ENCODE_FRAME_POINTER
#ifdef CONFIG_FRAME_POINTER
mov %esp, %ebp
orl $0x1, %ebp
#endif
.endm
.macro RESTORE_INT_REGS
popl %ebx
popl %ecx
@ -641,6 +657,7 @@ common_interrupt:
ASM_CLAC
addl $-0x80, (%esp) /* Adjust vector into the [-256, -1] range */
SAVE_ALL
ENCODE_FRAME_POINTER
TRACE_IRQS_OFF
movl %esp, %eax
call do_IRQ
@ -652,6 +669,7 @@ ENTRY(name) \
ASM_CLAC; \
pushl $~(nr); \
SAVE_ALL; \
ENCODE_FRAME_POINTER; \
TRACE_IRQS_OFF \
movl %esp, %eax; \
call fn; \
@ -786,6 +804,7 @@ END(spurious_interrupt_bug)
ENTRY(xen_hypervisor_callback)
pushl $-1 /* orig_ax = -1 => not a system call */
SAVE_ALL
ENCODE_FRAME_POINTER
TRACE_IRQS_OFF
/*
@ -840,6 +859,7 @@ ENTRY(xen_failsafe_callback)
jmp iret_exc
5: pushl $-1 /* orig_ax = -1 => not a system call */
SAVE_ALL
ENCODE_FRAME_POINTER
jmp ret_from_exception
.section .fixup, "ax"
@ -1067,6 +1087,7 @@ common_exception:
pushl %edx
pushl %ecx
pushl %ebx
ENCODE_FRAME_POINTER
cld
movl $(__KERNEL_PERCPU), %ecx
movl %ecx, %fs
@ -1099,6 +1120,7 @@ ENTRY(debug)
ASM_CLAC
pushl $-1 # mark this as an int
SAVE_ALL
ENCODE_FRAME_POINTER
xorl %edx, %edx # error code 0
movl %esp, %eax # pt_regs pointer
@ -1114,11 +1136,11 @@ ENTRY(debug)
.Ldebug_from_sysenter_stack:
/* We're on the SYSENTER stack. Switch off. */
movl %esp, %ebp
movl %esp, %ebx
movl PER_CPU_VAR(cpu_current_top_of_stack), %esp
TRACE_IRQS_OFF
call do_debug
movl %ebp, %esp
movl %ebx, %esp
jmp ret_from_exception
END(debug)
@ -1141,6 +1163,7 @@ ENTRY(nmi)
pushl %eax # pt_regs->orig_ax
SAVE_ALL
ENCODE_FRAME_POINTER
xorl %edx, %edx # zero error code
movl %esp, %eax # pt_regs pointer
@ -1159,10 +1182,10 @@ ENTRY(nmi)
* We're on the SYSENTER stack. Switch off. No one (not even debug)
* is using the thread stack right now, so it's safe for us to use it.
*/
movl %esp, %ebp
movl %esp, %ebx
movl PER_CPU_VAR(cpu_current_top_of_stack), %esp
call do_nmi
movl %ebp, %esp
movl %ebx, %esp
jmp .Lrestore_all_notrace
#ifdef CONFIG_X86_ESPFIX32
@ -1179,6 +1202,7 @@ ENTRY(nmi)
.endr
pushl %eax
SAVE_ALL
ENCODE_FRAME_POINTER
FIXUP_ESPFIX_STACK # %eax == %esp
xorl %edx, %edx # zero error code
call do_nmi
@ -1192,6 +1216,7 @@ ENTRY(int3)
ASM_CLAC
pushl $-1 # mark this as an int
SAVE_ALL
ENCODE_FRAME_POINTER
TRACE_IRQS_OFF
xorl %edx, %edx # zero error code
movl %esp, %eax # pt_regs pointer

10
arch/x86/entry/entry_64.S
View File

@ -469,6 +469,7 @@ END(irq_entries_start)
ALLOC_PT_GPREGS_ON_STACK
SAVE_C_REGS
SAVE_EXTRA_REGS
ENCODE_FRAME_POINTER
testb $3, CS(%rsp)
jz 1f
@ -985,6 +986,7 @@ ENTRY(xen_failsafe_callback)
ALLOC_PT_GPREGS_ON_STACK
SAVE_C_REGS
SAVE_EXTRA_REGS
ENCODE_FRAME_POINTER
jmp error_exit
END(xen_failsafe_callback)
@ -1028,6 +1030,7 @@ ENTRY(paranoid_entry)
cld
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
ENCODE_FRAME_POINTER 8
movl $1, %ebx
movl $MSR_GS_BASE, %ecx
rdmsr
@ -1075,6 +1078,7 @@ ENTRY(error_entry)
cld
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
ENCODE_FRAME_POINTER 8
xorl %ebx, %ebx
testb $3, CS+8(%rsp)
jz .Lerror_kernelspace
@ -1257,6 +1261,7 @@ ENTRY(nmi)
pushq %r13 /* pt_regs->r13 */
pushq %r14 /* pt_regs->r14 */
pushq %r15 /* pt_regs->r15 */
ENCODE_FRAME_POINTER
/*
* At this point we no longer need to worry about stack damage
@ -1270,11 +1275,10 @@ ENTRY(nmi)
/*
* Return back to user mode. We must *not* do the normal exit
* work, because we don't want to enable interrupts. Fortunately,
* do_nmi doesn't modify pt_regs.
* work, because we don't want to enable interrupts.
*/
SWAPGS
jmp restore_c_regs_and_iret
jmp restore_regs_and_iret
.Lnmi_from_kernel:
/*

16
arch/x86/include/asm/unwind.h
View File

@ -13,6 +13,7 @@ struct unwind_state {
int graph_idx;
#ifdef CONFIG_FRAME_POINTER
unsigned long *bp;
struct pt_regs *regs;
#else
unsigned long *sp;
#endif
@ -47,7 +48,15 @@ unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
if (unwind_done(state))
return NULL;
return state->bp + 1;
return state->regs ? &state->regs->ip : state->bp + 1;
}
static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
{
if (unwind_done(state))
return NULL;
return state->regs;
}
#else /* !CONFIG_FRAME_POINTER */
@ -58,6 +67,11 @@ unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
return NULL;
}
static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
{
return NULL;
}
#endif /* CONFIG_FRAME_POINTER */
#endif /* _ASM_X86_UNWIND_H */

74
arch/x86/kernel/unwind_frame.c
View File

@ -14,6 +14,9 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
if (unwind_done(state))
return 0;
if (state->regs && user_mode(state->regs))
return 0;
addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, *addr_p,
addr_p);
@ -21,6 +24,20 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);
/*
* This determines if the frame pointer actually contains an encoded pointer to
* pt_regs on the stack. See ENCODE_FRAME_POINTER.
*/
static struct pt_regs *decode_frame_pointer(unsigned long *bp)
{
unsigned long regs = (unsigned long)bp;
if (!(regs & 0x1))
return NULL;
return (struct pt_regs *)(regs & ~0x1);
}
static bool update_stack_state(struct unwind_state *state, void *addr,
size_t len)
{
@ -43,26 +60,59 @@ static bool update_stack_state(struct unwind_state *state, void *addr,
bool unwind_next_frame(struct unwind_state *state)
{
unsigned long *next_bp;
struct pt_regs *regs;
unsigned long *next_bp, *next_frame;
size_t next_len;
if (unwind_done(state))
return false;
/* have we reached the end? */
if (state->regs && user_mode(state->regs))
goto the_end;
/* get the next frame pointer */
if (state->regs)
next_bp = (unsigned long *)state->regs->bp;
else
next_bp = (unsigned long *)*state->bp;
/* make sure the next frame's data is accessible */
if (!update_stack_state(state, next_bp, FRAME_HEADER_SIZE))
return false;
/* is the next frame pointer an encoded pointer to pt_regs? */
regs = decode_frame_pointer(next_bp);
if (regs) {
next_frame = (unsigned long *)regs;
next_len = sizeof(*regs);
} else {
next_frame = next_bp;
next_len = FRAME_HEADER_SIZE;
}
/* make sure the next frame's data is accessible */
if (!update_stack_state(state, next_frame, next_len))
return false;
/* move to the next frame */
if (regs) {
state->regs = regs;
state->bp = NULL;
} else {
state->bp = next_bp;
state->regs = NULL;
}
return true;
the_end:
state->stack_info.type = STACK_TYPE_UNKNOWN;
return false;
}
EXPORT_SYMBOL_GPL(unwind_next_frame);
void __unwind_start(struct unwind_state *state, struct task_struct *task,
struct pt_regs *regs, unsigned long *first_frame)
{
unsigned long *bp, *frame;
size_t len;
memset(state, 0, sizeof(*state));
state->task = task;
@ -73,12 +123,22 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
}
/* set up the starting stack frame */
state->bp = get_frame_pointer(task, regs);
bp = get_frame_pointer(task, regs);
regs = decode_frame_pointer(bp);
if (regs) {
state->regs = regs;
frame = (unsigned long *)regs;
len = sizeof(*regs);
} else {
state->bp = bp;
frame = bp;
len = FRAME_HEADER_SIZE;
}
/* initialize stack info and make sure the frame data is accessible */
get_stack_info(state->bp, state->task, &state->stack_info,
get_stack_info(frame, state->task, &state->stack_info,
&state->stack_mask);
update_stack_state(state, state->bp, FRAME_HEADER_SIZE);
update_stack_state(state, frame, len);
/*
* The caller can provide the address of the first frame directly