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| 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/Kconfig | |
| parent | 8f7c0d8b23c3f5f740a48db31ebadef28af17a22 (diff) | |
| download | lwn-bea75b33895f7f87f0c40023e36a2d087e87ffa1.tar.gz lwn-bea75b33895f7f87f0c40023e36a2d087e87ffa1.zip | |
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/Kconfig')
| -rw-r--r-- | arch/x86/Kconfig | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index e18963e77cb1..e368fc0daa4a 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2446,9 +2446,27 @@ config CC_HAS_SLS config CC_HAS_RETURN_THUNK def_bool $(cc-option,-mfunction-return=thunk-extern) +config CC_HAS_ENTRY_PADDING + def_bool $(cc-option,-fpatchable-function-entry=16,16) + +config FUNCTION_PADDING_CFI + int + default 59 if FUNCTION_ALIGNMENT_64B + default 27 if FUNCTION_ALIGNMENT_32B + default 11 if FUNCTION_ALIGNMENT_16B + default 3 if FUNCTION_ALIGNMENT_8B + default 0 + +# Basically: FUNCTION_ALIGNMENT - 5*CFI_CLANG +# except Kconfig can't do arithmetic :/ +config FUNCTION_PADDING_BYTES + int + default FUNCTION_PADDING_CFI if CFI_CLANG + default FUNCTION_ALIGNMENT + config HAVE_CALL_THUNKS def_bool y - depends on RETHUNK && OBJTOOL + depends on CC_HAS_ENTRY_PADDING && RETHUNK && OBJTOOL config CALL_THUNKS def_bool n |