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Subject[PATCH 3.16 085/157] MIPS: scall64-o32: Fix indirect syscall number load
3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Aurelien Jarno <aurelien@aurel32.net>

commit 79b4a9cf0e2ea8203ce777c8d5cfa86c71eae86e upstream.

Commit 4c21b8fd8f14 (MIPS: seccomp: Handle indirect system calls (o32))
added indirect syscall detection for O32 processes running on MIPS64,
but it did not work correctly for big endian kernel/processes. The
reason is that the syscall number is loaded from ARG1 using the lw
instruction while this is a 64-bit value, so zero is loaded instead of
the syscall number.

Fix the code by using the ld instruction instead. When running a 32-bit
processes on a 64 bit CPU, the values are properly sign-extended, so it
ensures the value passed to syscall_trace_enter is correct.

Recent systemd versions with seccomp enabled whitelist the getpid
syscall for their internal processes (e.g. systemd-journald), but call
it through syscall(SYS_getpid). This fix therefore allows O32 big endian
systems with a 64-bit kernel to run recent systemd versions.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/mips/kernel/scall64-o32.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/mips/kernel/scall64-o32.S
+++ b/arch/mips/kernel/scall64-o32.S
@@ -124,7 +124,7 @@ trace_a_syscall:
subu t1, v0, __NR_O32_Linux
move a1, v0
bnez t1, 1f /* __NR_syscall at offset 0 */
- lw a1, PT_R4(sp) /* Arg1 for __NR_syscall case */
+ ld a1, PT_R4(sp) /* Arg1 for __NR_syscall case */
.set pop

1: jal syscall_trace_enter
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