Patch "x86/mpx: Fix instruction decoder condition" has been added to the 4.3-stable tree

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

x86/mpx: Fix instruction decoder condition

to the 4.3-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-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dave Hansen <[email protected]>
Date: Mon, 30 Nov 2015 16:31:13 -0800
Subject: x86/mpx: Fix instruction decoder condition

From: Dave Hansen <[email protected]>

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.

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

@@ -101,19 +101,19 @@ 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 [email protected] are

queue-4.3/x86-mm-add-barriers-and-document-switch_mm-vs-flush-synchronization.patch queue-4.3/x86-mm-improve-switch_mm-barrier-comments.patch queue-4.3/x86-mpx-fix-instruction-decoder-condition.patch