This is a note to let you know that I've just added the patch titled
ARM: 8692/1: mm: abort uaccess retries upon fatal signal
to the 4.12-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:
arm-8692-1-mm-abort-uaccess-retries-upon-fatal-signal.patch
and it can be found in the queue-4.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 746a272e44141af24a02f6c9b0f65f4c4598ed42 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@xxxxxxx>
Date: Tue, 22 Aug 2017 11:36:17 +0100
Subject: ARM: 8692/1: mm: abort uaccess retries upon fatal signal
From: Mark Rutland <mark.rutland@xxxxxxx>
commit 746a272e44141af24a02f6c9b0f65f4c4598ed42 upstream.
When there's a fatal signal pending, arm's do_page_fault()
implementation returns 0. The intent is that we'll return to the
faulting userspace instruction, delivering the signal on the way.
However, if we take a fatal signal during fixing up a uaccess, this
results in a return to the faulting kernel instruction, which will be
instantly retried, resulting in the same fault being taken forever. As
the task never reaches userspace, the signal is not delivered, and the
task is left unkillable. While the task is stuck in this state, it can
inhibit the forward progress of the system.
To avoid this, we must ensure that when a fatal signal is pending, we
apply any necessary fixup for a faulting kernel instruction. Thus we
will return to an error path, and it is up to that code to make forward
progress towards delivering the fatal signal.
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Reviewed-by: Steve Capper <steve.capper@xxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm/mm/fault.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -315,8 +315,11 @@ retry:
* signal first. We do not need to release the mmap_sem because
* it would already be released in __lock_page_or_retry in
* mm/filemap.c. */
- if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+ if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
+ if (!user_mode(regs))
+ goto no_context;
return 0;
+ }
/*
* Major/minor page fault accounting is only done on the
Patches currently in stable-queue which might be from mark.rutland@xxxxxxx are
queue-4.12/arm-8692-1-mm-abort-uaccess-retries-upon-fatal-signal.patch