From: Dave Hansen <dave@sr71.net>
To: linux-kernel@vger.kernel.org
Cc: dave.hansen@linux.intel.com, x86@kernel.org, luto@kernel.org,
fenghua.yu@intel.com, yu-cheng.yu@intel.com
Subject: Re: [PATCH] x86, fpu: fix 32-bit signal frame handling
Date: Thu, 12 Nov 2015 14:50:50 -0800 [thread overview]
Message-ID: <564517CA.7090600@sr71.net> (raw)
In-Reply-To: <20151111002354.A0799571@viggo.jf.intel.com>
On 11/10/2015 04:23 PM, Dave Hansen wrote:
> For MPX, this leads to the most permissive state and means we
> silently lose bounds violations. I think this would also mean
> that we could lose *ANY* FPU/SSE/AVX state. I'm not sure why
> no one has spotted this bug.
FWIW, I looked at this a little more today.
We lose all extended state for our "extended xfeatures", also known as
state component numbers >=2 (AVX, MPX, AVX-512, PKEYs)... But we retain
the state for FP/SSE state. So we lose the top half of the AVX
registers (the bottom half are SSE state).
I also did a little objdump'ing and grep'ing in a 32-bit distro.
There's no sign of actual use of the ymm registers.
Basically, it appears nobody has taken a 64-bit Sandybridge or later
CPU, put a 32-bit distro on it that had a >=3.7 kernel on it and tried
to use AVX instructions. Or, if they did, they got random corruption
and gave up before actually diagnosing the problem. :)
next prev parent reply other threads:[~2015-11-12 22:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-11 0:23 [PATCH] x86, fpu: fix 32-bit signal frame handling Dave Hansen
2015-11-12 13:28 ` [tip:x86/urgent] x86/fpu: Fix " tip-bot for Dave Hansen
2015-11-12 22:50 ` Dave Hansen [this message]
2015-11-27 10:06 ` [PATCH] x86, fpu: fix " Ingo Molnar
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