Patch "x86/mpx: Fix instruction decoder condition" has been added to the 4.1-stable tree

Patch "x86/mpx: Fix instruction decoder condition" has been added to the 4.1-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    x86/mpx: Fix instruction decoder condition

to the 4.1-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:
     x86-mpx-fix-instruction-decoder-condition.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 8e8efe0379bd93e8219ca0fc6fa80b5dd85b09cb Mon Sep 17 00:00:00 2001
From: Dave Hansen <dave.hansen@linux.intel.com>
Date: Mon, 30 Nov 2015 16:31:13 -0800
Subject: x86/mpx: Fix instruction decoder condition

From: Dave Hansen <dave.hansen@linux.intel.com>

commit 8e8efe0379bd93e8219ca0fc6fa80b5dd85b09cb upstream.

MPX decodes instructions in order to tell which bounds register
was violated.  Part of this decoding involves looking at the "REX
prefix" which is a special instrucion prefix used to retrofit
support for new registers in to old instructions.

The X86_REX_*() macros are defined to return actual bit values:

	#define X86_REX_R(rex) ((rex) & 4)

*not* boolean values.  However, the MPX code was checking for
them like they were booleans.  This might have led to us
mis-decoding the "REX prefix" and giving false information out to
userspace about bounds violations.  X86_REX_B() actually is bit 1,
so this is really only broken for the X86_REX_X() case.

Fix the conditionals up to tolerate the non-boolean values.

Fixes: fcc7ffd67991 "x86, mpx: Decode MPX instruction to get bound violation information"
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: Dave Hansen <dave@sr71.net>
Link: http://lkml.kernel.org/r/20151201003113.D800C1E0@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/mm/mpx.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -120,19 +120,19 @@ static int get_reg_offset(struct insn *i
 	switch (type) {
 	case REG_TYPE_RM:
 		regno = X86_MODRM_RM(insn->modrm.value);
-		if (X86_REX_B(insn->rex_prefix.value) == 1)
+		if (X86_REX_B(insn->rex_prefix.value))
 			regno += 8;
 		break;
 
 	case REG_TYPE_INDEX:
 		regno = X86_SIB_INDEX(insn->sib.value);
-		if (X86_REX_X(insn->rex_prefix.value) == 1)
+		if (X86_REX_X(insn->rex_prefix.value))
 			regno += 8;
 		break;
 
 	case REG_TYPE_BASE:
 		regno = X86_SIB_BASE(insn->sib.value);
-		if (X86_REX_B(insn->rex_prefix.value) == 1)
+		if (X86_REX_B(insn->rex_prefix.value))
 			regno += 8;
 		break;
 


Patches currently in stable-queue which might be from dave.hansen@linux.intel.com are

queue-4.1/x86-mm-add-barriers-and-document-switch_mm-vs-flush-synchronization.patch
queue-4.1/x86-mm-improve-switch_mm-barrier-comments.patch
queue-4.1/x86-mpx-fix-instruction-decoder-condition.patch