linux-kernel - Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

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Message-ID: <CAObL_7FMuomx-fAKUHA2mHAQrLSOOKF0=4ugkvk2b8rfFXk3EQ@mail.gmail.com>
Date:	Thu, 12 Jan 2012 09:02:49 -0800
From:	Andrew Lutomirski <luto@....edu>
To:	Will Drewry <wad@...omium.org>
Cc:	linux-kernel@...r.kernel.org, keescook@...omium.org,
	john.johansen@...onical.com, serge.hallyn@...onical.com,
	coreyb@...ux.vnet.ibm.com, pmoore@...hat.com, eparis@...hat.com,
	djm@...drot.org, torvalds@...ux-foundation.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
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	gregkh@...e.de, dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com
Subject: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

On Wed, Jan 11, 2012 at 9:25 AM, Will Drewry <wad@...omium.org> wrote:
> This patch adds support for seccomp mode 2.  This mode enables dynamic
> enforcement of system call filtering policy in the kernel as specified
> by a userland task.  The policy is expressed in terms of a BPF program,
> as is used for userland-exposed socket filtering.  Instead of network
> data, the BPF program is evaluated over struct user_regs_struct at the
> time of the system call (as retrieved using regviews).
>

There's some seccomp-related code in the vsyscall emulation path in
arch/x86/kernel/vsyscall_64.c.  How should time(), getcpu(), and
gettimeofday() be handled?  If you want filtering to work, there
aren't any real syscall registers to inspect, but they could be
synthesized.

Preventing a malicious task from figuring out approximately what time
it is is basically impossible because of the way that vvars work.  I
don't know how to change that efficiently.

--Andy
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