linux-kernel - Re: [PATCH] selftests: add seccomp suite

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Message-ID: <CAGXu5jK3xuCqJoE9W+b_5yH+TffDDaL5tDFyZhKRx_K-Qqqk2g@mail.gmail.com>
Date:	Wed, 17 Jun 2015 11:12:56 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Shuah Khan <shuahkh@....samsung.com>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	"David S. Miller" <davem@...emloft.net>,
	Arnd Bergmann <arnd@...db.de>, Joe Perches <joe@...ches.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] selftests: add seccomp suite

On Wed, Jun 17, 2015 at 12:31 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
> On Tue, 2015-06-16 at 10:54 -0700, Kees Cook wrote:
>> This imports the existing seccomp test suite into the kernel's selftests
>> tree. It contains extensive testing of seccomp features and corner cases.
>> There remain additional tests to move into the kernel tree, but they have
>> not yet been ported to all the architectures seccomp supports:
>> https://github.com/redpig/seccomp/tree/master/tests
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  MAINTAINERS                                    |    1 +
>>  tools/testing/selftests/Makefile               |    1 +
>>  tools/testing/selftests/seccomp/.gitignore     |    1 +
>>  tools/testing/selftests/seccomp/Makefile       |   10 +
>>  tools/testing/selftests/seccomp/seccomp_bpf.c  | 2109 ++++++++++++++++++++++++
>>  tools/testing/selftests/seccomp/test_harness.h |  537 ++++++
>
>
> Thanks very much for adding this, it would have been very helpful recently when
> I was trying to get seccomp filter working on powerpc :)
>
> I get one failure in TRACE_syscall.syscall_dropped:
>
>   seccomp_bpf.c:1394:TRACE_syscall.syscall_dropped:Expected 1 (1) == syscall(207) (18446744073709551615)
>
>
> So it looks like we're returning -1 instead of 1.
>
> That's probably a bug in our handling of the return value, or maybe an
> inconsistency across the arches. I'll try and find time to dig into it.

Ah-ha! Excellent. Did you add an implementation for change_syscall()
in seccomp_bpf.c? I don't have a powerpc method in there. I would have
expected both TRACE_syscall.syscall_redirected and .syscall_dropped to
fail without that.

If you did, maybe something isn't right with regs.SYSCALL_RET ? That's
where the return value being tested on a skipped syscall is stored.

Thanks for testing!

-Kees

-- 
Kees Cook
Chrome OS Security
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