[3.16.y-ckt stable] Patch "perf/x86: Fix copy_from_user_nmi() return if range is not ok" has been added to staging queue

[Luis Henriques]

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

    perf/x86: Fix copy_from_user_nmi() return if range is not ok

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/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt18.

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 7028d9235baaa3415f44c45243a9024a862da191 Mon Sep 17 00:00:00 2001
From: Yann Droneaud <ydroneaud at opteya.com>
Date: Mon, 22 Jun 2015 21:38:43 +0200
Subject: perf/x86: Fix copy_from_user_nmi() return if range is not ok

commit ebf2d2689de551d90965090bb991fc640a0c0d41 upstream.

Commit 0a196848ca36 ("perf: Fix arch_perf_out_copy_user default"),
changes copy_from_user_nmi() to return the number of
remaining bytes so that it behave like copy_from_user().

Unfortunately, when the range is outside of the process
memory, the return value  is still the number of byte
copied, eg. 0, instead of the remaining bytes.

As all users of copy_from_user_nmi() were modified as
part of commit 0a196848ca36, the function should be
fixed to return the total number of bytes if range is
not correct.

Signed-off-by: Yann Droneaud <ydroneaud at opteya.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Link: http://lkml.kernel.org/r/1435001923-30986-1-git-send-email-ydroneaud@opteya.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Cc: Yann Droneaud <ydroneaud at opteya.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/lib/usercopy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index ddf9ecb53cc3..e342586db6e4 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -20,7 +20,7 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
 	unsigned long ret;

 	if (__range_not_ok(from, n, TASK_SIZE))
-		return 0;
+		return n;

 	/*
 	 * Even though this function is typically called from NMI/IRQ context