linux-kernel - Re: [RFC PATCH 11/12] selftests/seccomp: Make seccomp tests work on big endian

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Date:	Wed, 15 Jul 2015 08:16:10 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	"linuxppc-dev@...abs.org" <linuxppc-dev@...abs.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>, strosake@...ux.vnet.ibm.com,
	bogdan.purcareata@...escale.com
Subject: Re: [RFC PATCH 11/12] selftests/seccomp: Make seccomp tests work on
 big endian

On Wed, Jul 15, 2015 at 12:37 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
> The seccomp_bpf test uses BPF_LD|BPF_W|BPF_ABS to load 32-bit values
> from seccomp_data->args. On big endian machines this will load the high
> word of the argument, which is not what the test wants.
>
> Borrow a hack from samples/seccomp/bpf-helper.h which changes the offset
> on big endian to account for this.
>
> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> ---
>  tools/testing/selftests/seccomp/seccomp_bpf.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> index b2374c131340..51adb9afb511 100644
> --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> @@ -82,7 +82,13 @@ struct seccomp_data {
>  };
>  #endif
>
> +#if __BYTE_ORDER == __LITTLE_ENDIAN
>  #define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]))
> +#elif __BYTE_ORDER == __BIG_ENDIAN
> +#define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]) + sizeof(__u32))
> +#else
> +#error "wut?"
> +#endif

Ah-ha! Yes, thanks. Could you change the #error to something that
describes the particular (impossible) failure condition? "wut? Unknown
__BYTE_ORDER?!". Not a huge deal, but I always like verbose errors. :)
Especially for "impossible" situations. :)

-Kees

>
>  #define SIBLING_EXIT_UNKILLED  0xbadbeef
>  #define SIBLING_EXIT_FAILURE   0xbadface
> --
> 2.1.0
>



-- 
Kees Cook
Chrome OS Security
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