[3.19.y-ckt stable] Patch "x86/mpx: Add temporary variable to reduce masking" has been added to staging queue

[Kamal Mostafa]

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

    x86/mpx: Add temporary variable to reduce masking

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-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 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 0dffd65cce74d518bb357a7370cfe46cc79782cf Mon Sep 17 00:00:00 2001
From: Dave Hansen <dave.hansen at linux.intel.com>
Date: Sun, 7 Jun 2015 11:37:04 -0700
Subject: x86/mpx: Add temporary variable to reduce masking

commit a1149fc83a1f97612e72ec24a0bdbabff7b85e77 upstream.

When we allocate a bounds table, we call mmap(), then add a
"valid" bit to the value before storing it in to the bounds
directory.

If we fail along the way, we go and mask that valid bit
_back_ out.  That seems a little silly, and this makes it
much more clear when we have a plain address versus an
actual table _entry_.

Signed-off-by: Dave Hansen <dave.hansen at linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx at linutronix.de>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Dave Hansen <dave at sr71.net>
Cc: H. Peter Anvin <hpa at zytor.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Link: http://lkml.kernel.org/r/20150607183704.3D69D5F4@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
[ kamal: 3.19-stable prereq for "46561c3 x86/mpx: Do proper get_user() when
  running 32-bit binaries on 64-bit kernels" ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/mm/mpx.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 4d1c11c..9c208e4 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -409,6 +409,7 @@ static int allocate_bt(long __user *bd_entry)
 	unsigned long expected_old_val = 0;
 	unsigned long actual_old_val = 0;
 	unsigned long bt_addr;
+	unsigned long bd_new_entry;
 	int ret = 0;

 	/*
@@ -421,7 +422,7 @@ static int allocate_bt(long __user *bd_entry)
 	/*
 	 * Set the valid flag (kinda like _PAGE_PRESENT in a pte)
 	 */
-	bt_addr = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
+	bd_new_entry = bt_addr | MPX_BD_ENTRY_VALID_FLAG;

 	/*
 	 * Go poke the address of the new bounds table in to the
@@ -435,7 +436,7 @@ static int allocate_bt(long __user *bd_entry)
 	 * of the MPX code that have to pagefault_disable().
 	 */
 	ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,
-					   expected_old_val, bt_addr);
+					   expected_old_val, bd_new_entry);
 	if (ret)
 		goto out_unmap;

@@ -465,7 +466,7 @@ static int allocate_bt(long __user *bd_entry)
 	}
 	return 0;
 out_unmap:
-	vm_munmap(bt_addr & MPX_BT_ADDR_MASK, MPX_BT_SIZE_BYTES);
+	vm_munmap(bt_addr, MPX_BT_SIZE_BYTES);
 	return ret;
 }

--
1.9.1