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. */
> +#else
> +#define RSEQ_SIG_DATA RSEQ_SIG_CODE
> +#endif
> +
> +#define RSEQ_SIG RSEQ_SIG_DATA
>
> #define rseq_smp_mb() __asm__ __volatile__ ("dmb ish" ::: "memory")
> #define rseq_smp_rmb() __asm__ __volatile__ ("dmb ishld" ::: "memory")
> @@ -121,7 +134,7 @@ do { \
>
> #define RSEQ_ASM_DEFINE_ABORT(label, abort_label) \
> " b 222f\n" \
> - " .inst " __rseq_str(RSEQ_SIG) "\n" \
> + " .inst " __rseq_str(RSEQ_SIG_CODE) "\n" \
I don't think this is right; the .inst directive _should_ emit the value
in the instruction stream endianness (i.e. LE, regardless of the data
endianness).
That's certainly the case with the kernel.org crosstool GCC:
[mark@lakrids:/mnt/data/tests/inst-test]% cat test.c
void func(void)
{
asm volatile(".inst 0xd4000001");
}
[mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-gcc -c test.c
[mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-objdump -d test.o
test.o: file format elf64-littleaarch64
Disassembly of section .text:
0000000000000000 <func>:
0: d4000001 svc #0x0
4: d503201f nop
8: d65f03c0 ret
[mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-gcc -mbig-endian -c test.c
[mark@lakrids:/mnt/data/tests/inst-test]% usekorg 8.1.0 aarch64-linux-objdump -d test.o
test.o: file format elf64-bigaarch64
Disassembly of section .text:
0000000000000000 <func>:
0: d4000001 svc #0x0
4: d503201f nop
8: d65f03c0 ret
Have you tested this? Is there some toolchain that doesn't get this
right?
Thanks,
Mark.
