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arm64: extable: consolidate definitions 

In subsequent patches we'll alter the structure and usage of struct
exception_table_entry. For inline assembly, we create these using the
`_ASM_EXTABLE()` CPP macro defined in <asm/uaccess.h>, and for plain
assembly code we use the `_asm_extable()` GAS macro defined in
<asm/assembler.h>, which are largely identical save for different
escaping and stringification requirements.

This patch moves the common definitions to a new <asm/asm-extable.h>
header, so that it's easier to keep the two in-sync, and to remove the
implication that these are only used for uaccess helpers (as e.g.
load_unaligned_zeropad() is only used on kernel memory, and depends upon
`_ASM_EXTABLE()`.

At the same time, a few minor modifications are made for clarity and in
preparation for subsequent patches:

* The structure creation is factored out into an `__ASM_EXTABLE_RAW()`
  macro. This will make it easier to support different fixup variants in
  subsequent patches without needing to update all users of
  `_ASM_EXTABLE()`, and makes it easier to see tha the CPP and GAS
  variants of the macros are structurally identical.

  For the CPP macro, the stringification of fields is left to the
  wrapper macro, `_ASM_EXTABLE()`, as in subsequent patches it will be
  necessary to stringify fields in wrapper macros to safely concatenate
  strings which cannot be token-pasted together in CPP.

* The fields of the structure are created separately on their own lines.
  This will make it easier to add/remove/modify individual fields
  clearly.

* Additional parentheses are added around the use of macro arguments in
  field definitions to avoid any potential problems with evaluation due
  to operator precedence, and to make errors upon misuse clearer.

* USER() is moved into <asm/asm-uaccess.h>, as it is not required by all
  assembly code, and is already refered to by comments in that file.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20211019160219.5202-8-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2021-10-19 17:02:13 +01:00 committed by Will Deacon
parent 286fba6c2a
commit 819771cc28
5 changed files with 58 additions and 35 deletions
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48
arch/arm64/include/asm/asm-extable.h Normal file
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@ -0,0 +1,48 @@
/* SPDX-License-Identifier: GPL-2.0-only */
#ifndef __ASM_ASM_EXTABLE_H
#define __ASM_ASM_EXTABLE_H
#ifdef __ASSEMBLY__
#define __ASM_EXTABLE_RAW(insn, fixup) \
.pushsection __ex_table, "a"; \
.align 3; \
.long ((insn) - .); \
.long ((fixup) - .); \
.popsection;
/*
* Create an exception table entry for `insn`, which will branch to `fixup`
* when an unhandled fault is taken.
*/
.macro _asm_extable, insn, fixup
__ASM_EXTABLE_RAW(\insn, \fixup)
.endm
/*
* Create an exception table entry for `insn` if `fixup` is provided. Otherwise
* do nothing.
*/
.macro _cond_extable, insn, fixup
.ifnc \fixup,
_asm_extable \insn, \fixup
.endif
.endm
#else /* __ASSEMBLY__ */
#include <linux/stringify.h>
#define __ASM_EXTABLE_RAW(insn, fixup) \
".pushsection __ex_table, \"a\"\n" \
".align 3\n" \
".long ((" insn ") - .)\n" \
".long ((" fixup ") - .)\n" \
".popsection\n"
#define _ASM_EXTABLE(insn, fixup) \
__ASM_EXTABLE_RAW(#insn, #fixup)
#endif /* __ASSEMBLY__ */
#endif /* __ASM_ASM_EXTABLE_H */

7
arch/arm64/include/asm/asm-uaccess.h
View File

@ -3,10 +3,11 @@
#define __ASM_ASM_UACCESS_H
#include <asm/alternative-macros.h>
#include <asm/asm-extable.h>
#include <asm/assembler.h>
#include <asm/kernel-pgtable.h>
#include <asm/mmu.h>
#include <asm/sysreg.h>
#include <asm/assembler.h>
/*
* User access enabling/disabling macros.
@ -58,6 +59,10 @@ alternative_else_nop_endif
.endm
#endif
#define USER(l, x...) \
9999: x; \
_asm_extable 9999b, l
/*
* Generate the assembly for LDTR/STTR with exception table entries.
* This is complicated as there is no post-increment or pair versions of the

29
arch/arm64/include/asm/assembler.h
View File

@ -14,9 +14,10 @@
#include <asm-generic/export.h>
#include <asm/asm-offsets.h>
#include <asm/alternative.h>
#include <asm/asm-bug.h>
#include <asm/asm-extable.h>
#include <asm/asm-offsets.h>
#include <asm/cpufeature.h>
#include <asm/cputype.h>
#include <asm/debug-monitors.h>
@ -129,32 +130,6 @@ alternative_endif
.endr
.endm
/*
* Create an exception table entry for `insn`, which will branch to `fixup`
* when an unhandled fault is taken.
*/
.macro _asm_extable, insn, fixup
.pushsection __ex_table, "a"
.align 3
.long (\insn - .), (\fixup - .)
.popsection
.endm
/*
* Create an exception table entry for `insn` if `fixup` is provided. Otherwise
* do nothing.
*/
.macro _cond_extable, insn, fixup
.ifnc \fixup,
_asm_extable \insn, \fixup
.endif
.endm
#define USER(l, x...) \
9999: x; \
_asm_extable 9999b, l
/*
* Register aliases.
*/

7
arch/arm64/include/asm/uaccess.h
View File

@ -18,6 +18,7 @@
#include <linux/kasan-checks.h>
#include <linux/string.h>
#include <asm/asm-extable.h>
#include <asm/cpufeature.h>
#include <asm/mmu.h>
#include <asm/mte.h>
@ -70,12 +71,6 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
#define access_ok(addr, size) __range_ok(addr, size)
#define _ASM_EXTABLE(from, to) \
" .pushsection __ex_table, \"a\"\n" \
" .align 3\n" \
" .long (" #from " - .), (" #to " - .)\n" \
" .popsection\n"
/*
* User access enabling/disabling.
*/

2
arch/arm64/lib/clear_user.S
View File

@ -4,7 +4,7 @@
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
#include <asm/asm-uaccess.h>
.text