Patch "MIPS: Don't unwind to user mode with EVA" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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

    MIPS: Don't unwind to user mode with EVA

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-don-t-unwind-to-user-mode-with-eva.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 a816b306c62195b7c43c92cb13330821a96bdc27 Mon Sep 17 00:00:00 2001
From: James Hogan <james.hogan@imgtec.com>
Date: Fri, 4 Dec 2015 22:25:01 +0000
Subject: MIPS: Don't unwind to user mode with EVA

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

commit a816b306c62195b7c43c92cb13330821a96bdc27 upstream.

When unwinding through IRQs and exceptions, the unwinding only continues
if the PC is a kernel text address, however since EVA it is possible for
user and kernel address ranges to overlap, potentially allowing
unwinding to continue to user mode if the user PC happens to be in the
kernel text address range.

Adjust the check to also ensure that the register state from before the
exception is actually running in kernel mode, i.e. !user_mode(regs).

I don't believe any harm can come of this problem, since the PC is only
output, the stack pointer is checked to ensure it resides within the
task's stack page before it is dereferenced in search of the return
address, and the return address register is similarly only output (if
the PC is in a leaf function or the beginning of a non-leaf function).

However unwind_stack() is only meant for unwinding kernel code, so to be
correct the unwind should stop there.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11700/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -457,7 +457,7 @@ unsigned long notrace unwind_stack_by_ad
 		    *sp + sizeof(*regs) <= stack_page + THREAD_SIZE - 32) {
 			regs = (struct pt_regs *)*sp;
 			pc = regs->cp0_epc;
-			if (__kernel_text_address(pc)) {
+			if (!user_mode(regs) && __kernel_text_address(pc)) {
 				*sp = regs->regs[29];
 				*ra = regs->regs[31];
 				return pc;


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

queue-4.4/mips64-r6-r2-emulation-bugfix.patch
queue-4.4/mips-fix-uapi-include-in-exported-asm-siginfo.h.patch
queue-4.4/mips-disable-preemption-during-prctl-pr_set_fp_mode.patch
queue-4.4/mips-fix-sigreturn-via-vdso-on-micromips-kernel.patch
queue-4.4/mips-fix-siginfo.h-to-use-strict-posix-types.patch
queue-4.4/mips-don-t-unwind-to-user-mode-with-eva.patch
queue-4.4/mips-vdso-build-with-fno-strict-aliasing.patch
queue-4.4/mips-fix-watchpoint-restoration.patch
queue-4.4/mips-build-micromips-vdso-for-micromips-kernels.patch
queue-4.4/mips-math-emu-fix-jalr-emulation-when-rd-0.patch
queue-4.4/mips-fix-msa-ld_-st_-asm-macros-to-use-ptr_addu.patch
queue-4.4/mips-avoid-using-unwind_stack-with-usermode.patch
queue-4.4/mips-prevent-restoration-of-msa-context-in-non-msa-kernels.patch
queue-4.4/mips-use-copy_s.fmt-rather-than-copy_u.fmt.patch