Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

[Will Deacon]

On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
> Handle compiling with -mbig-endian on aarch64, which generates binaries
> with mixed code vs data endianness (little endian code, big endian
> data).
> 
> Else mismatch between code endianness for the generated signatures and
> data endianness for the RSEQ_SIG parameter passed to the rseq
> registration will trigger application segmentation faults when the
> kernel try to abort rseq critical sections.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CC: Joel Fernandes <joelaf@xxxxxxxxxx>
> CC: Catalin Marinas <catalin.marinas@xxxxxxx>
> CC: Dave Watson <davejwatson@xxxxxx>
> CC: Will Deacon <will.deacon@xxxxxxx>
> CC: Shuah Khan <shuah@xxxxxxxxxx>
> CC: Andi Kleen <andi@xxxxxxxxxxxxxx>
> CC: linux-kselftest@xxxxxxxxxxxxxxx
> CC: "H . Peter Anvin" <hpa@xxxxxxxxx>
> CC: Chris Lameter <cl@xxxxxxxxx>
> CC: Russell King <linux@xxxxxxxxxxxxxxxx>
> CC: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
> CC: "Paul E . McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
> CC: Paul Turner <pjt@xxxxxxxxxx>
> CC: Boqun Feng <boqun.feng@xxxxxxxxx>
> CC: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
> CC: Ben Maurer <bmaurer@xxxxxx>
> CC: linux-api@xxxxxxxxxxxxxxx
> CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> ---
>  tools/testing/selftests/rseq/rseq-arm64.h | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/rseq/rseq-arm64.h b/tools/testing/selftests/rseq/rseq-arm64.h
> index b41a2a48e965..200dae9e4208 100644
> --- a/tools/testing/selftests/rseq/rseq-arm64.h
> +++ b/tools/testing/selftests/rseq/rseq-arm64.h
> @@ -6,7 +6,20 @@
>   * (C) Copyright 2018 - Will Deacon <will.deacon@xxxxxxx>
>   */
>  
> -#define RSEQ_SIG	0xd428bc00	/* BRK #0x45E0 */
> +/*
> + * aarch64 -mbig-endian generates mixed endianness code vs data:
> + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
> + * matches code endianness.
> + */
> +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
> +
> +#ifdef __AARCH64EB__
> +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */

It would be neater to implement swab32 and use that with RSEQ_SIG_CODE,
but either way:

Acked-by: Will Deacon <will.deacon@xxxxxxx>

Will