Messages in this thread | | | Date | Thu, 18 Aug 2022 09:28:28 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86/kvm, objtool: Avoid fastop ENDBR from being sealed |
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On Wed, Aug 17, 2022 at 06:10:45PM -0700, Josh Poimboeuf wrote: > 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:
Nice!, should I 'borrow' this and respin the patch or you want to make a real patch out of it?
> 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)
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