[3.13.y.z extended stable] Patch "ARM: 8178/1: fix set_tls for !CONFIG_KUSER_HELPERS" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ARM: 8178/1: fix set_tls for !CONFIG_KUSER_HELPERS

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From f8b5bb46092ec9c7dc09810d577b3dbe7f7ecbd7 Mon Sep 17 00:00:00 2001
From: Nathan Lynch <nathan_lynch at mentor.com>
Date: Mon, 29 Sep 2014 19:11:36 +0100
Subject: ARM: 8178/1: fix set_tls for !CONFIG_KUSER_HELPERS

commit 9cc6d9e5daaa147a9a3e31557efcb331989e77be upstream.

Joachim Eastwood reports that commit fbfb872f5f41 "ARM: 8148/1: flush
TLS and thumbee register state during exec" causes a boot-time crash
on a Cortex-M4 nommu system:

Freeing unused kernel memory: 68K (281e5000 - 281f6000)
Unhandled exception: IPSR = 00000005 LR = fffffff1
CPU: 0 PID: 1 Comm: swapper Not tainted 3.17.0-rc6-00313-gd2205fa30aa7 #191
task: 29834000 ti: 29832000 task.ti: 29832000
PC is at flush_thread+0x2e/0x40
LR is at flush_thread+0x21/0x40
pc : [<2800954a>] lr : [<2800953d>] psr: 4100000b
sp : 29833d60 ip : 00000000 fp : 00000001
r10: 00003cf8 r9 : 29b1f000 r8 : 00000000
r7 : 29b0bc00 r6 : 29834000 r5 : 29832000 r4 : 29832000
r3 : ffff0ff0 r2 : 29832000 r1 : 00000000 r0 : 282121f0
xPSR: 4100000b
CPU: 0 PID: 1 Comm: swapper Not tainted 3.17.0-rc6-00313-gd2205fa30aa7 #191
[<2800afa5>] (unwind_backtrace) from [<2800a327>] (show_stack+0xb/0xc)
[<2800a327>] (show_stack) from [<2800a963>] (__invalid_entry+0x4b/0x4c)

The problem is that set_tls is attempting to clear the TLS location in
the kernel-user helper page, which isn't set up on V7M.

Fix this by guarding the write to the kuser helper page with
a CONFIG_KUSER_HELPERS ifdef.

Fixes: fbfb872f5f41 ARM: 8148/1: flush TLS and thumbee register state during exec

Reported-by: Joachim Eastwood <manabian at gmail.com>
Tested-by: Joachim Eastwood <manabian at gmail.com>
Signed-off-by: Nathan Lynch <nathan_lynch at mentor.com>
Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm/include/asm/tls.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm/include/asm/tls.h b/arch/arm/include/asm/tls.h
index 36172ad..5f833f7 100644
--- a/arch/arm/include/asm/tls.h
+++ b/arch/arm/include/asm/tls.h
@@ -81,6 +81,7 @@ static inline void set_tls(unsigned long val)
 			asm("mcr p15, 0, %0, c13, c0, 3"
 			    : : "r" (val));
 		} else {
+#ifdef CONFIG_KUSER_HELPERS
 			/*
 			 * User space must never try to access this
 			 * directly.  Expect your app to break
@@ -89,6 +90,7 @@ static inline void set_tls(unsigned long val)
 			 * entry-armv.S for details)
 			 */
 			*((unsigned int *)0xffff0ff0) = val;
+#endif
 		}

 	}
--
1.9.1