linux-kernel - Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF

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Message-ID: <4F3D7DD4.6070103@zytor.com>
Date:	Thu, 16 Feb 2012 14:06:12 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Will Drewry <wad@...omium.org>
CC:	Markus Gutschke <markus@...omium.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
	davem@...emloft.net, mingo@...hat.com, oleg@...hat.com,
	peterz@...radead.org, rdunlap@...otime.net, mcgrathr@...omium.org,
	tglx@...utronix.de, luto@....edu, eparis@...hat.com,
	serge.hallyn@...onical.com, djm@...drot.org, scarybeasts@...il.com,
	indan@....nu, pmoore@...hat.com, akpm@...ux-foundation.org,
	corbet@....net, eric.dumazet@...il.com, keescook@...omium.org
Subject: Re: [PATCH v8 3/8] seccomp: add system call filtering using BPF

On 02/16/2012 01:51 PM, Will Drewry wrote:
>>
>> Put the bloody bit in there and let the pattern program make that decision.
> 
> Easy enough to add a bit for the mode: 32-bit or 64-bit.  It seemed
> like a waste of cycles for every 32-bit program or every 64-bit
> program to check to see that its calling convention hadn't changed,
> but it does take away a valid decision the pattern program should be
> making.
> 
> I'll add a flag for 32bit/64bit while cleaning up seccomp_data. I
> think that will properly encapsulate the is_compat_task() behavior in
> a way that is stable for compat and non-compat tasks to use.  If
> there's a more obvious way, I'm all ears.
> 

is_compat_task() is not going to be the right thing for x86 going
forward, as we're introducing the x32 ABI (which uses the normal x86-64
entry point, but with different eax numbers, and bit 30 set.)

The actual state is the TS_COMPAT flag in the thread_info structure,
which currently matches is_compat_task(), but perhaps we should add a
new helper function syscall_namespace() or something like that...

Either that or we can just use another bit in the syscall number field...

	-hpa

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

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