[3.16.y-ckt stable] Patch "vm: make stack guard page errors return VM_FAULT_SIGSEGV rather than SIGBUS" has been added to staging queue

[Luis Henriques]

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

    vm: make stack guard page errors return VM_FAULT_SIGSEGV rather than SIGBUS

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt6.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From d88d4f16c7ef71544052b4cc10703be21bb56726 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds at linux-foundation.org>
Date: Thu, 29 Jan 2015 11:15:17 -0800
Subject: vm: make stack guard page errors return VM_FAULT_SIGSEGV rather than
 SIGBUS

commit 9c145c56d0c8a0b62e48c8d71e055ad0fb2012ba upstream.

The stack guard page error case has long incorrectly caused a SIGBUS
rather than a SIGSEGV, but nobody actually noticed until commit
fee7e49d4514 ("mm: propagate error from stack expansion even for guard
page") because that error case was never actually triggered in any
normal situations.

Now that we actually report the error, people noticed the wrong signal
that resulted.  So far, only the test suite of libsigsegv seems to have
actually cared, but there are real applications that use libsigsegv, so
let's not wait for any of those to break.

Reported-and-tested-by: Takashi Iwai <tiwai at suse.de>
Tested-by: Jan Engelhardt <jengelh at inai.de>
Acked-by: Heiko Carstens <heiko.carstens at de.ibm.com> # "s390 still compiles and boots"
Cc: linux-arch at vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 mm/memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index dda1dc6d92dd..769bc8906b2d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2639,7 +2639,7 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,

 	/* Check if we need to add a guard page to the stack */
 	if (check_stack_guard_page(vma, address) < 0)
-		return VM_FAULT_SIGBUS;
+		return VM_FAULT_SIGSEGV;

 	/* Use the zero-page for reads */
 	if (!(flags & FAULT_FLAG_WRITE)) {
--
2.1.4