[PATCH] ARM: Call syscall_trace_exit even when system call skipped

Timothy E Baldwin T.E.Baldwin99 at members.leeds.ac.uk
Sat Feb 3 07:21:12 PST 2018

On at least x86 and ARM64, and as documented in the ptrace man page
a skipped system call will still cause a syscall exit ptrace stop.

Previous to this commit 32-bit ARM did not, resulting in strace
being confused when seccomp skips system calls.

This change also impacts programs that use ptrace to skip system calls.

Fixes: ad75b51459ae ("ARM: 7579/1: arch/allow a scno of -1 to not cause a SIGILL")
Signed-off-by: Timothy E Baldwin <T.E.Baldwin99 at members.leeds.ac.uk>
 arch/arm/kernel/entry-common.S | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 99c908226065..88a65157307d 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -288,16 +288,15 @@ __sys_trace:
 	cmp	scno, #-1			@ skip the syscall?
 	bne	2b
 	add	sp, sp, #S_OFF			@ restore stack
-	b	ret_slow_syscall
-	str	r0, [sp, #S_R0 + S_OFF]!	@ save returned r0
+	enable_irq_notrace
 	mov	r0, sp
 	bl	syscall_trace_exit
 	b	ret_slow_syscall
-	enable_irq_notrace
+	str	r0, [sp, #S_R0 + S_OFF]!	@ save returned r0
 	mov	r0, sp
 	bl	syscall_trace_exit
 	b	ret_slow_syscall

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