[PATCH 4.4 154/159] ARM: 8802/1: Call syscall_trace_exit even when system call skipped

From: Greg Kroah-Hartman
Date: Fri Nov 22 2019 - 06:24:43 EST

From: Timothy E Baldwin <T.E.Baldwin99@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit f18aef742c8fbd68e280dff0a63ba0ca6ee8ad85 ]

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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Eugene Syromyatnikov <evgsyr@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Tested-by: Eugene Syromyatnikov <evgsyr@xxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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 e969b18d9ff93..d31f0300d2c98 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -261,16 +261,15 @@ __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