linux-kernel - Re: [PATCH v8 07/10] x86, mpx: decode MPX instruction to get bound violation information

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Message-ID: <alpine.DEB.2.10.1409121943430.4178@nanos>
Date:	Fri, 12 Sep 2014 19:48:27 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Dave Hansen <dave.hansen@...el.com>,
	Qiaowei Ren <qiaowei.ren@...el.com>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 07/10] x86, mpx: decode MPX instruction to get bound
 violation information

On Fri, 12 Sep 2014, H. Peter Anvin wrote:
> The correct limit is 15 bytes, not anything else, so this is a bug in
> the existing decoder.  A sequence of bytes longer than 15 bytes will

Fine. Lets fix it there.

> #UD, regardless of being "otherwise valid".

> Keep in mind the instruction may not be aligned, and you could fit an
> instruction plus a jump and still overrun a page in 15 bytes.

Fair enough. OTOH, I doubt that a text mapping will end exactly at
that jump after the MPX instruction.

So that's simple to fix.

Kill the hardcoded limit in lib/insn.c and let the callsites hand in a
lenght argument. So you can still use it for MPX and avoid 200 lines
of blindly copied and slightly different decoder code.

Thanks,

	tglx
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