[3.19.y-ckt stable] Patch "MIPS: Avoid using unwind_stack() with usermode" has been added to the 3.19.y-ckt tree

Kamal Mostafa kamal at canonical.com
Wed Jul 6 21:00:35 UTC 2016


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

    MIPS: Avoid using unwind_stack() with usermode

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt23.

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

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 4989639e43cef5d745319246e1414abe78e58763 Mon Sep 17 00:00:00 2001
From: James Hogan <james.hogan at imgtec.com>
Date: Fri, 4 Dec 2015 22:25:02 +0000
Subject: MIPS: Avoid using unwind_stack() with usermode

commit 81a76d7119f63c359750e4adeff922a31ad1135f upstream.

When showing backtraces in response to traps, for example crashes and
address errors (usually unaligned accesses) when they are set in debugfs
to be reported, unwind_stack will be used if the PC was in the kernel
text address range. However since EVA it is possible for user and kernel
address ranges to overlap, and even without EVA userland can still
trigger an address error by jumping to a KSeg0 address.

Adjust the check to also ensure that it was running in kernel mode. I
don't believe any harm can come of this problem, since unwind_stack() is
sufficiently defensive, however it is only meant for unwinding kernel
code, so to be correct it should use the raw backtracing instead.

Signed-off-by: James Hogan <james.hogan at imgtec.com>
Reviewed-by: Leonid Yegoshin <Leonid.Yegoshin at imgtec.com>
Cc: linux-mips at linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11701/
Signed-off-by: Ralf Baechle <ralf at linux-mips.org>
(cherry picked from commit d2941a975ac745c607dfb590e92bb30bc352dad9)
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/mips/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 7dd15e9..af1475f 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -141,7 +141,7 @@ static void show_backtrace(struct task_struct *task, const struct pt_regs *regs)
 	if (!task)
 		task = current;

-	if (raw_show_trace || !__kernel_text_address(pc)) {
+	if (raw_show_trace || user_mode(regs) || !__kernel_text_address(pc)) {
 		show_raw_backtrace(sp);
 		return;
 	}
--
2.7.4





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