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

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Date:	Thu, 18 Jun 2015 11:00:44 -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 11:41 PM, Michael Ellerman <mpe@...erman.id.au> wrote:
> On Wed, 2015-06-17 at 11:12 -0700, Kees Cook wrote:
>> 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.
>
> Yeah I did add a change_syscall() implementation, patch below.

Great!

>> 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.
>
> Yeah I saw that too, and I think you're probably right that's where the problem
> is. It doesn't seem to matter what I put in SYSCALL_RET I always get -1, so I
> think there's a bug in my kernel code.
>
> Will try and work it out tonight.
>
> cheers
>
>
> diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> index c5abe7fd7590..1bced19c54fb 100644
> --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> @@ -14,6 +14,7 @@
>  #include <linux/filter.h>
>  #include <sys/prctl.h>
>  #include <sys/ptrace.h>
> +#include <sys/types.h>
>  #include <sys/user.h>
>  #include <linux/prctl.h>
>  #include <linux/ptrace.h>
> @@ -1199,6 +1200,10 @@ TEST_F(TRACE_poke, getpid_runs_normally)
>  # define ARCH_REGS     struct user_pt_regs
>  # define SYSCALL_NUM   regs[8]
>  # define SYSCALL_RET   regs[0]
> +#elif defined(__powerpc__)
> +# define ARCH_REGS     struct pt_regs
> +# define SYSCALL_NUM   gpr[0]
> +# define SYSCALL_RET   gpr[3]
>  #else
>  # error "Do not know how to find your architecture's registers and syscalls"
>  #endif
> @@ -1246,6 +1251,10 @@ void change_syscall(struct __test_metadata *_metadata,
>                 EXPECT_EQ(0, ret);
>         }
>
> +#elif defined(__powerpc__)
> +       {
> +               regs.SYSCALL_NUM = syscall;
> +       }

This can be collapsed into the first #if test with the other
architectures, but otherwise looks great.

>  #else
>         ASSERT_EQ(1, 0) {
>                 TH_LOG("How is the syscall changed on this architecture?");
> @@ -1396,6 +1405,8 @@ TEST_F(TRACE_syscall, syscall_dropped)
>  #  define __NR_seccomp 383
>  # elif defined(__aarch64__)
>  #  define __NR_seccomp 277
> +# elif defined(__powerpc__)
> +#  define __NR_seccomp 358
>  # else
>  #  warning "seccomp syscall number unknown for this architecture"
>  #  define __NR_seccomp 0xffff
>
>
>

Thanks!

-Kees


-- 
Kees Cook
Chrome OS Security
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