diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2022-09-15 13:11:18 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-10-17 16:41:10 +0200 |
| commit | bea75b33895f7f87f0c40023e36a2d087e87ffa1 (patch) | |
| tree | 301d9fc0cc4db3df6746e8163186cab5bf436632 /arch/x86/include/asm/linkage.h | |
| parent | 8f7c0d8b23c3f5f740a48db31ebadef28af17a22 (diff) | |
| download | linux-bea75b33895f7f87f0c40023e36a2d087e87ffa1.tar.bz2 | |
x86/Kconfig: Introduce function padding
Now that all functions are 16 byte aligned, add 16 bytes of NOP
padding in front of each function. This prepares things for software
call stack tracking and kCFI/FineIBT.
This significantly increases kernel .text size, around 5.1% on a
x86_64-defconfig-ish build.
However, per the random access argument used for alignment, these 16
extra bytes are code that wouldn't be used. Performance measurements
back this up by showing no significant performance regressions.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111146.950884492@infradead.org
Diffstat (limited to 'arch/x86/include/asm/linkage.h')
| -rw-r--r-- | arch/x86/include/asm/linkage.h | 51 |
1 files changed, 48 insertions, 3 deletions
diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h index c2d6e2733b11..45e0df850645 100644 --- a/arch/x86/include/asm/linkage.h +++ b/arch/x86/include/asm/linkage.h @@ -15,8 +15,19 @@ #define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT, 0x90; #define __ALIGN_STR __stringify(__ALIGN) -#define ASM_FUNC_ALIGN __ALIGN_STR -#define __FUNC_ALIGN __ALIGN +#if defined(CONFIG_CALL_THUNKS) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO) +#define FUNCTION_PADDING .skip CONFIG_FUNCTION_ALIGNMENT, 0x90; +#else +#define FUNCTION_PADDING +#endif + +#if (CONFIG_FUNCTION_ALIGNMENT > 8) && !defined(__DISABLE_EXPORTS) && !defined(BULID_VDSO) +# define __FUNC_ALIGN __ALIGN; FUNCTION_PADDING +#else +# define __FUNC_ALIGN __ALIGN +#endif + +#define ASM_FUNC_ALIGN __stringify(__FUNC_ALIGN) #define SYM_F_ALIGN __FUNC_ALIGN #ifdef __ASSEMBLY__ @@ -45,11 +56,45 @@ #endif /* __ASSEMBLY__ */ +/* + * Depending on -fpatchable-function-entry=N,N usage (CONFIG_CALL_THUNKS) the + * CFI symbol layout changes. + * + * Without CALL_THUNKS: + * + * .align FUNCTION_ALIGNMENT + * __cfi_##name: + * .skip FUNCTION_PADDING, 0x90 + * .byte 0xb8 + * .long __kcfi_typeid_##name + * name: + * + * With CALL_THUNKS: + * + * .align FUNCTION_ALIGNMENT + * __cfi_##name: + * .byte 0xb8 + * .long __kcfi_typeid_##name + * .skip FUNCTION_PADDING, 0x90 + * name: + * + * In both cases the whole thing is FUNCTION_ALIGNMENT aligned and sized. + */ + +#ifdef CONFIG_CALL_THUNKS +#define CFI_PRE_PADDING +#define CFI_POST_PADDING .skip CONFIG_FUNCTION_PADDING_BYTES, 0x90; +#else +#define CFI_PRE_PADDING .skip CONFIG_FUNCTION_PADDING_BYTES, 0x90; +#define CFI_POST_PADDING +#endif + #define __CFI_TYPE(name) \ SYM_START(__cfi_##name, SYM_L_LOCAL, SYM_A_NONE) \ - .fill 11, 1, 0x90 ASM_NL \ + CFI_PRE_PADDING \ .byte 0xb8 ASM_NL \ .long __kcfi_typeid_##name ASM_NL \ + CFI_POST_PADDING \ SYM_FUNC_END(__cfi_##name) /* SYM_TYPED_FUNC_START -- use for indirectly called globals, w/ CFI type */ |