Patch "x86/alternatives: Fix optimize_nops() checking" has been added to the 4.4-stable tree

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

x86/alternatives: Fix optimize_nops() checking

to the 4.4-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-4.4 subdirectory.

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

From: Borislav Petkov <[email protected]>
Date: Wed, 10 Jan 2018 12:28:16 +0100
Subject: x86/alternatives: Fix optimize_nops() checking

From: Borislav Petkov <[email protected]>

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.

---
 arch/x86/kernel/alternative.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

@@ -339,9 +339,12 @@ 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 [email protected] are

queue-4.4/x86-microcode-intel-extend-bdw-late-loading-with-a-revision-check.patch queue-4.4/x86-alternatives-fix-optimize_nops-checking.patch