MIPS: Fix seccomp syscall argument for MIPS64

This change “MIPS: Fix seccomp syscall argument for MIPS64″ in Linux kernel is authored by Markos Chandras <markos.chandras [at] imgtec.com> on Thu Aug 13 08:47:59 2015 +0100.

MIPS: Fix seccomp syscall argument for MIPS64

Commit 4c21b8fd8f14 ("MIPS: seccomp: Handle indirect system calls (o32)")
fixed indirect system calls on O32 but it also introduced a bug for MIPS64
where it erroneously modified the v0 (syscall) register with the assumption
that the sycall offset hasn't been taken into consideration. This breaks
seccomp on MIPS64 n64 and n32 ABIs. We fix this by replacing the addition
with a move instruction.

Fixes: 4c21b8fd8f14 ("MIPS: seccomp: Handle indirect system calls (o32)")
Cc: <stable@vger.kernel.org> # 3.15+
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10951/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit 9f16143.

There are 4 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 arch/mips/kernel/scall64-64.S  | 2 +-
 arch/mips/kernel/scall64-n32.S | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kernel/scall64-64.S b/arch/mips/kernel/scall64-64.S
index ad4d4463..a6f6b76 100644
--- a/arch/mips/kernel/scall64-64.S
+++ b/arch/mips/kernel/scall64-64.S
@@ -80,7 +80,7 @@ syscall_trace_entry:
 	SAVE_STATIC
 	move	s0, t2
 	move	a0, sp
-	daddiu	a1, v0, __NR_64_Linux
+	move	a1, v0
 	jal	syscall_trace_enter
 
 	bltz	v0, 2f			# seccomp failed? Skip syscall
diff --git a/arch/mips/kernel/scall64-n32.S b/arch/mips/kernel/scall64-n32.S
index 446cc65..4b20106 100644
--- a/arch/mips/kernel/scall64-n32.S
+++ b/arch/mips/kernel/scall64-n32.S
@@ -72,7 +72,7 @@ n32_syscall_trace_entry:
 	SAVE_STATIC
 	move	s0, t2
 	move	a0, sp
-	daddiu	a1, v0, __NR_N32_Linux
+	move	a1, v0
 	jal	syscall_trace_enter
 
 	bltz	v0, 2f			# seccomp failed? Skip syscall

The commit for this change in Linux stable tree is 9f16143 (patch).

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