Message-ID: <4F459139.8010603@zytor.com>
Date: Wed, 22 Feb 2012 17:07:05 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andrew Lutomirski <luto@mit.edu>
CC: Indan Zupancic <indan@nul.nu>, Will Drewry <wad@chromium.org>,
        Ben Hutchings <bhutchings@solarflare.com>,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
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        netdev@vger.kernel.org, x86@kernel.org, arnd@arndb.de,
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        tglx@linutronix.de, eparis@redhat.com, serge.hallyn@canonical.com,
        djm@mindrot.org, scarybeasts@gmail.com, pmoore@redhat.com,
        akpm@linux-foundation.org, corbet@lwn.net, eric.dumazet@gmail.com,
        markus@chromium.org, keescook@chromium.org
Subject: Re: [PATCH v10 05/11] seccomp: add system call filtering using BPF
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On 02/22/2012 03:51 PM, Andrew Lutomirski wrote:
> On Wed, Feb 22, 2012 at 3:46 PM, Indan Zupancic <indan@nul.nu> wrote:
>> On Wed, February 22, 2012 20:47, Will Drewry wrote:
>>> On Wed, Feb 22, 2012 at 8:23 AM, Ben Hutchings
>>>> I would have thought the way to make sure the architecture is always
>>>> checked is to pack it together with the syscall number.
>>
>> I missed that suggestion, putting the syscall number and arch in one
>> data field would indeed make it harder to not check the arch.
> 
> Is there enough room?  On x86-64 at least, rax could conceivably be
> extended to 64 bits some day.  Bit 30 is already spoken for by x32.
> 

No it couldn't, because we mask off the high 32 bits and thus it could
(theoretically) break user space.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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