Patch "MIPS: Avoid accidental raw backtrace" has been added to the 4.4-stable tree

Patch "MIPS: Avoid accidental raw backtrace" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    MIPS: Avoid accidental raw backtrace

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mips-avoid-accidental-raw-backtrace.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 854236363370995a609a10b03e35fd3dc5e9e4a1 Mon Sep 17 00:00:00 2001
From: James Hogan <james.hogan@imgtec.com>
Date: Thu, 29 Jun 2017 15:05:04 +0100
Subject: MIPS: Avoid accidental raw backtrace

From: James Hogan <james.hogan@imgtec.com>

commit 854236363370995a609a10b03e35fd3dc5e9e4a1 upstream.

Since commit 81a76d7119f6 ("MIPS: Avoid using unwind_stack() with
usermode") show_backtrace() invokes the raw backtracer when
cp0_status & ST0_KSU indicates user mode to fix issues on EVA kernels
where user and kernel address spaces overlap.

However this is used by show_stack() which creates its own pt_regs on
the stack and leaves cp0_status uninitialised in most of the code paths.
This results in the non deterministic use of the raw back tracer
depending on the previous stack content.

show_stack() deals exclusively with kernel mode stacks anyway, so
explicitly initialise regs.cp0_status to KSU_KERNEL (i.e. 0) to ensure
we get a useful backtrace.

Fixes: 81a76d7119f6 ("MIPS: Avoid using unwind_stack() with usermode")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16656/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/kernel/traps.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -194,6 +194,8 @@ void show_stack(struct task_struct *task
 {
 	struct pt_regs regs;
 	mm_segment_t old_fs = get_fs();
+
+	regs.cp0_status = KSU_KERNEL;
 	if (sp) {
 		regs.regs[29] = (unsigned long)sp;
 		regs.regs[31] = 0;


Patches currently in stable-queue which might be from james.hogan@imgtec.com are

queue-4.4/mips-avoid-accidental-raw-backtrace.patch