Patch "x86/alternatives: Fix optimize_nops() checking" has been added to the 4.9-stable tree

Patch "x86/alternatives: Fix optimize_nops() checking" has been added to the 4.9-stable tree

[gregkh]

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

    x86/alternatives: Fix optimize_nops() checking

to the 4.9-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-alternatives-fix-optimize_nops-checking.patch
and it can be found in the queue-4.9 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 612e8e9350fd19cae6900cf36ea0c6892d1a0dca Mon Sep 17 00:00:00 2001
From: Borislav Petkov <bp@suse.de>
Date: Wed, 10 Jan 2018 12:28:16 +0100
Subject: x86/alternatives: Fix optimize_nops() checking

From: Borislav Petkov <bp@suse.de>

commit 612e8e9350fd19cae6900cf36ea0c6892d1a0dca upstream.

The alternatives code checks only the first byte whether it is a NOP, but
with NOPs in front of the payload and having actual instructions after it
breaks the "optimized' test.

Make sure to scan all bytes before deciding to optimize the NOPs in there.

Reported-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
Cc: Paul Turner <pjt@google.com>
Link: https://lkml.kernel.org/r/20180110112815.mgciyf5acwacphkq@pd.tnic
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kernel/alternative.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -340,9 +340,12 @@ done:
 static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr)
 {
 	unsigned long flags;
+	int i;
 
-	if (instr[0] != 0x90)
-		return;
+	for (i = 0; i < a->padlen; i++) {
+		if (instr[i] != 0x90)
+			return;
+	}
 
 	local_irq_save(flags);
 	add_nops(instr + (a->instrlen - a->padlen), a->padlen);


Patches currently in stable-queue which might be from bp@suse.de are

queue-4.9/x86-microcode-intel-extend-bdw-late-loading-with-a-revision-check.patch
queue-4.9/x86-cpufeatures-make-cpu-bugs-sticky.patch
queue-4.9/x86-cpu-amd-make-lfence-a-serializing-instruction.patch
queue-4.9/x86-cpu-factor-out-application-of-forced-cpu-caps.patch
queue-4.9/x86-cpu-merge-bugs.c-and-bugs_64.c.patch
queue-4.9/x86-alternatives-fix-optimize_nops-checking.patch
queue-4.9/x86-cpu-amd-use-lfence_rdtsc-in-preference-to-mfence_rdtsc.patch