linux-kernel - Re: [PATCH] x86, boot: fix word-size assumptions in has

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Message-ID: <CAGXu5jKnabMPHF2iNph5QFue0ZADSXoCzoCJXPgh_QC7SUN8mw@mail.gmail.com>
Date:	Wed, 29 Jan 2014 08:57:40 -0800
From:	Kees Cook <keescook@...omium.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Aaron Durbin <adurbin@...gle.com>,
	Eric Northup <digitaleric@...gle.com>,
	Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...gle.com>,
	Mathias Krause <minipli@...glemail.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86, boot: fix word-size assumptions in has_eflag()
 inline asm

On Wed, Jan 29, 2014 at 4:01 AM, David Woodhouse <dwmw2@...radead.org> wrote:
> Commit dd78b97367bd575918204cc89107c1479d3fc1a7 ("x86, boot: Move CPU
> flags out of cpucheck") introduced ambiguous inline asm in the
> has_eflag() function. We want the instruction to be 'pushfl', but we
> just say 'pushf' and hope the compiler does what we wanted.
>
> When building with 'clang -m16', it won't, because clang doesn't use
> the horrid '.code16gcc' hack that even 'gcc -m16' uses internally.
>
> Say what we mean and don't make the compiler make assumptions.
>
> Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>

Yes, excellent point. Thanks!

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

-- 
Kees Cook
Chrome OS Security
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