ARM: 7579/1: arch/allow a scno of -1 to not cause a SIGILL
On tracehook-friendly platforms, a system call number of -1 falls
through without running much code or taking much action.
ARM is different. This adds a short-circuit check in the trace path to
avoid any additional work, as suggested by Russell King, to make sure
that ARM behaves the same way as other platforms.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Will Drewry <wad@chromium.org>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index b621871..ee81dbc 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -448,7 +448,10 @@
ldmccia r1, {r0 - r6} @ have to reload r0 - r6
stmccia sp, {r4, r5} @ and update the stack args
ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine
- b 2b
+ cmp scno, #-1 @ skip the syscall?
+ bne 2b
+ add sp, sp, #S_OFF @ restore stack
+ b ret_slow_syscall
__sys_trace_return:
str r0, [sp, #S_R0 + S_OFF]! @ save returned r0
