linux-kernel - Re: [PATCH v10 05/11] seccomp: add system call filtering using BPF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CABqD9hZjpxE4V3cMSNYbECbPDMHyXfgFTr+Y3_fv20MivqQJ-w@mail.gmail.com>
Date:	Wed, 22 Feb 2012 14:01:09 -0600
From:	Will Drewry <wad@...omium.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Indan Zupancic <indan@....nu>, 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, pmoore@...hat.com,
	akpm@...ux-foundation.org, corbet@....net, eric.dumazet@...il.com,
	markus@...omium.org, keescook@...omium.org
Subject: Re: [PATCH v10 05/11] seccomp: add system call filtering using BPF

On Wed, Feb 22, 2012 at 1:53 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 02/22/2012 11:47 AM, Will Drewry wrote:
>>>
>>> I highly disagree with every filter having to check the mode: Filters that
>>> don't check the arch on e.g. x86 are buggy, so they have to check it, even
>>> if it's a 32-bit or 64-bit only system, the filters can't know that and
>>> needs to check the arch at every syscall entry. All other info in the data
>>> depends on the arch, because of this there isn't much code to share between
>>> the two archs, so you can as well have one filter for each arch.
>>>
>>> Alternative approach: Tell the arch at filter install time and only run the
>>> filters with the same arch as the current system call. If no filters are run,
>>> deny the systemcall.
>>
>> This was roughly how I first implemented compat and non-compat
>> support.  It causes some implicit behavior across inheritance that is
>> not nice though.
>>
>
> This is trivially doable at the BPF level, right?  Just make this the
> first instruction in the program (either deny or jump to a separate
> program branch)... and then there is still "one program" without any
> weird inheritance issues?

Exactly, and that's what the patch does now (after your feedback :)

ld arch
je arch, 1, 0
ret SECCOMP_RET_KILL
<rest of bpf program>

At this point, I don't think it makes sense to do it a different way
than just in the BPF program even if it does mean leaving out the
check could leave the program open to compat-style bugs.  At least a
shared library and/or good practices should be able to catch that
error.

thanks!
will
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/