linux-kernel - Re: [PATCH 05/29] x86: Base IBT bits

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Date:   Fri, 18 Feb 2022 22:26:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrew Cooper <Andrew.Cooper3@...rix.com>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "joao@...rdrivepizza.com" <joao@...rdrivepizza.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "samitolvanen@...gle.com" <samitolvanen@...gle.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "alyssa.milburn@...el.com" <alyssa.milburn@...el.com>
Subject: Re: [PATCH 05/29] x86: Base IBT bits

On Fri, Feb 18, 2022 at 08:49:45PM +0000, Andrew Cooper wrote:
> On 18/02/2022 16:49, Peter Zijlstra wrote:
> > +/*
> > + * A bit convoluted, but matches both endbr32 and endbr64 without
> > + * having either as literal in the text.
> > + */
> > +static inline bool is_endbr(const void *addr)
> > +{
> > +	unsigned int val = ~*(unsigned int *)addr;
> > +	val |= 0x01000000U;
> > +	return val == ~0xfa1e0ff3;
> > +}
> 
> At this point, I feel I've earned an "I told you so". :)

Ha! I actually have a note to double-check this. But yes, I'll stuff
that piece of asm in so I can forget about it.