[PATCH 3.19.y-ckt 006/128] x86/mpx: Add temporary variable to reduce masking

[Kamal Mostafa]

3.19.8-ckt12 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20150607183704.3D69D5F4@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
[ 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@xxxxxxxxxxxxx>
---
 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

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