Patch "MIPS: Avoid using unwind_stack() with usermode" has been added to the 4.5-stable tree

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

MIPS: Avoid using unwind_stack() with usermode

to the 4.5-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-using-unwind_stack-with-usermode.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: James Hogan <[email protected]>
Date: Fri, 4 Dec 2015 22:25:02 +0000
Subject: MIPS: Avoid using unwind_stack() with usermode

From: James Hogan <[email protected]>

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.

Patchwork: https://patchwork.linux-mips.org/patch/11701/

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

@@ -144,7 +144,7 @@ static void show_backtrace(struct task_s
 	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;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/mips64-r6-r2-emulation-bugfix.patch queue-4.5/mips-fix-uapi-include-in-exported-asm-siginfo.h.patch queue-4.5/mips-disable-preemption-during-prctl-pr_set_fp_mode.patch queue-4.5/mips-fix-sigreturn-via-vdso-on-micromips-kernel.patch queue-4.5/mips-fix-siginfo.h-to-use-strict-posix-types.patch queue-4.5/mips-don-t-unwind-to-user-mode-with-eva.patch queue-4.5/mips-vdso-build-with-fno-strict-aliasing.patch queue-4.5/mips-fix-watchpoint-restoration.patch queue-4.5/mips-build-micromips-vdso-for-micromips-kernels.patch queue-4.5/mips-math-emu-fix-jalr-emulation-when-rd-0.patch queue-4.5/mips-fix-msa-ld_-st_-asm-macros-to-use-ptr_addu.patch queue-4.5/mips-avoid-using-unwind_stack-with-usermode.patch queue-4.5/mips-prevent-restoration-of-msa-context-in-non-msa-kernels.patch queue-4.5/mips-use-copy_s.fmt-rather-than-copy_u.fmt.patch