[3.13.y-ckt stable] Patch "powerpc: do_notify_resume can be called with bad thread_info flags argument" has been added to staging queue

[Kamal Mostafa]

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

    powerpc: do_notify_resume can be called with bad thread_info flags argument

to the linux-3.13.y-queue branch of the 3.13.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-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt12.

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

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 38c96f03e228598aea71749ddb77efefb6f5998a Mon Sep 17 00:00:00 2001
From: Anton Blanchard <anton at samba.org>
Date: Fri, 31 Oct 2014 16:50:57 +1100
Subject: powerpc: do_notify_resume can be called with bad thread_info flags
 argument

commit 808be31426af57af22268ef0fcb42617beb3d15b upstream.

Back in 7230c5644188 ("powerpc: Rework lazy-interrupt handling") we
added a call out to restore_interrupts() (written in c) before calling
do_notify_resume:

        bl      restore_interrupts
        addi    r3,r1,STACK_FRAME_OVERHEAD
        bl      do_notify_resume

Unfortunately do_notify_resume takes two arguments, the second one
being the thread_info flags:

void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)

We do populate r4 (the second argument) earlier, but
restore_interrupts() is free to muck it up all it wants. My guess is
the gcc compiler gods shone down on us and its register allocator
never used r4. Sometimes, rarely, luck is on our side.

LLVM on the other hand did trample r4.

Signed-off-by: Anton Blanchard <anton at samba.org>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
[ kamal: backport to 3.13-stable: context ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/powerpc/kernel/entry_64.S | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index fb5ba6d..088dca5 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -660,7 +660,13 @@ _GLOBAL(ret_from_except_lite)
 	b	.ret_from_except_lite

 2:	bl	.save_nvgprs
+	/*
+	 * Use a non volatile GPR to save and restore our thread_info flags
+	 * across the call to restore_interrupts.
+	 */
+	mr	r30,r4
 	bl	.restore_interrupts
+	mr	r4,r30
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	.do_notify_resume
 	b	.ret_from_except
--
1.9.1