linux-kernel - Re: [PATCH v2.1 2/3] objtool,x86: Additionally decode: mov %rsp, (%reg)

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Date:   Wed, 10 Feb 2021 10:31:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Miroslav Benes <mbenes@...e.cz>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Julien Thierry <jthierry@...hat.com>,
        Kees Cook <keescook@...omium.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2.1 2/3] objtool,x86: Additionally decode: mov %rsp,
 (%reg)

On Wed, Feb 10, 2021 at 10:08:51AM +0100, Peter Zijlstra wrote:
> +				/* skip nontrivial SIB */
> +				if (modrm_rm == 4 && sib != 0x24)
> +					break;

Hmm,, maybe that should be:

	if (modrm_rm == 4 && !(sib == 0x24 && rex_b == rex_x))

Because what we have is that once we have a SIB byte, rex_b is for
sib_base and rex_x is always sib_index, and we need to ensure that
sib_base == sib_index for the trivial case.


/me changes...