linux-kernel - Re: [PATCH] x86/ibt: Implement FineIBT

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Message-ID: <202210182215.19844E9F21@keescook>
Date:   Tue, 18 Oct 2022 22:16:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, Sami Tolvanen <samitolvanen@...gle.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT

On Tue, Oct 18, 2022 at 10:09:23PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 18, 2022 at 11:09:13AM -0700, Kees Cook wrote:
> 
> > > +#ifdef CONFIG_FINEIBT
> > > +/*
> > > + * kCFI						FineIBT
> > > + *
> > > + * __cfi_\func:					__cfi_\func:
> > > + *	movl   $0x12345678,%eax			     endbr64			// 4
> > 
> > kCFI emits endbr64 here first too ...
> > 
> > > + *	nop					     subl   $0x12345678,%r10d   // 7
> > > + *	nop					     jz     1f			// 2
> > > + *	nop					     ud2			// 2
> > > + *	nop					1:   nop			// 1
> > > + *	nop
> > > + *	nop
> > > + *	nop
> > > + *	nop
> > > + *	nop
> > > + *	nop
> > > + *	nop
> 
> It does not; it does emit ENDBR at the start of the regular symbol
> though:

Oh duh, sorry, yes.

-- 
Kees Cook