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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Timothy E Baldwin <T.E.Baldwin99@members.leeds.ac.uk>,
        Eugene Syromyatnikov <evgsyr@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Russell King <rmk+kernel@armlinux.org.uk>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 214/222] ARM: 8802/1: Call syscall_trace_exit even when system call skipped
Date:   Fri, 22 Nov 2019 11:29:14 +0100
Message-Id: <20191122100917.916466078@linuxfoundation.org>
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From: Timothy E Baldwin <T.E.Baldwin99@members.leeds.ac.uk>

[ 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@members.leeds.ac.uk>
Signed-off-by: Eugene Syromyatnikov <evgsyr@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Eugene Syromyatnikov <evgsyr@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 d69adfb3d79e6..178a2a9606595 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -263,16 +263,15 @@ __sys_trace:
 	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
+__sys_trace_return_nosave:
+	enable_irq_notrace
 	mov	r0, sp
 	bl	syscall_trace_exit
 	b	ret_slow_syscall
 
-__sys_trace_return_nosave:
-	enable_irq_notrace
+__sys_trace_return:
+	str	r0, [sp, #S_R0 + S_OFF]!	@ save returned r0
 	mov	r0, sp
 	bl	syscall_trace_exit
 	b	ret_slow_syscall
-- 
2.20.1