[PATCH 3.18 01/86] MIPS: scall64-o32: Fix indirect syscall number load

From: Greg Kroah-Hartman
Date: Wed May 15 2019 - 06:59:45 EST

From: Aurelien Jarno <aurelien@xxxxxxxxxxx>

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@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v3.15+
Reviewed-by: Philippe Mathieu-Daudà <f4bug@xxxxxxxxx>
Signed-off-by: Paul Burton <paul.burton@xxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: James Hogan <jhogan@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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