From bea75b33895f7f87f0c40023e36a2d087e87ffa1 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 15 Sep 2022 13:11:18 +0200 Subject: 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 Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20220915111146.950884492@infradead.org --- arch/x86/Kconfig | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) (limited to 'arch/x86/Kconfig') 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 -- cgit v1.2.3