From 0479a42d4c15bd554f54d89d12bf68218e3e70da Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 22 Jun 2023 16:27:13 +0200 Subject: [PATCH] x86/cfi: Extend {JMP,CAKK}_NOSPEC comment With the introduction of kCFI these helpers are no longer equivalent to C indirect calls and should be used with care. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Kees Cook Reviewed-by: Sami Tolvanen Link: https://lkml.kernel.org/r/20230622144321.360957723%40infradead.org --- arch/x86/include/asm/nospec-branch.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 55388c9..1a65cf4 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -234,6 +234,10 @@ * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple * indirect jmp/call which may be susceptible to the Spectre variant 2 * attack. + * + * NOTE: these do not take kCFI into account and are thus not comparable to C + * indirect calls, take care when using. The target of these should be an ENDBR + * instruction irrespective of kCFI. */ .macro JMP_NOSPEC reg:req #ifdef CONFIG_RETPOLINE -- 2.7.4