>From 4a7887c6dbbac4f9e05870455581a3e526b2d5d9 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Wed, 17 Aug 2022 18:10:45 -0700 Subject: [PATCH] x86/kvm, objtool: Avoid fastop ENDBR from being sealed On Wed, Aug 17, 2022 at 12:56:15PM +0200, Peter Zijlstra wrote: > Add (yet another) annotation to inhibit objtool from sealing a specific > ENDBR instance. Nah, just add a throwaway reference to the function. Then no objtool change is needed: --- arch/x86/include/asm/ibt.h | 10 ++++++++++ arch/x86/kvm/emulate.c | 3 ++- 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/ibt.h b/arch/x86/include/asm/ibt.h index 689880eca9ba..3ae795150374 100644 --- a/arch/x86/include/asm/ibt.h +++ b/arch/x86/include/asm/ibt.h @@ -31,6 +31,16 @@ #define __noendbr __attribute__((nocf_check)) +/* + * Create a dummy function pointer reference to prevent objtool from marking + * the function as needing to be "sealed" (i.e. ENDBR converted to NOP by + * apply_ibt_endbr()). + */ +#define IBT_NOSEAL(fname) \ + ".pushsection .discard.endbr.noseal\n\t" \ + _ASM_PTR fname "\n\t" \ + ".popsection\n\t" + static inline __attribute_const__ u32 gen_endbr(void) { u32 endbr; diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index f8382abe22ff..88623add0db4 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -316,7 +316,8 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop); ".align " __stringify(FASTOP_SIZE) " \n\t" \ ".type " name ", @function \n\t" \ name ":\n\t" \ - ASM_ENDBR + ASM_ENDBR \ + IBT_NOSEAL(name) #define FOP_FUNC(name) \ __FOP_FUNC(#name) -- 2.31.1