From: Kees Cook <keescook@chromium.org>
Date: Thu, 15 Nov 2012 21:12:17 +0000 (+0100)
Subject: ARM: 7579/1: arch/allow a scno of -1 to not cause a SIGILL
X-Git-Tag: v3.8-rc1~147^2~1^4~7
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=ad75b51459ae076a0d406391496f81b897bf6992;p=linux-2.6-block.git

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 b621871dd277..ee81dbc6fa10 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -448,7 +448,10 @@ __sys_trace:
 	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