Patch "x86/cpu: Fix bootup crashes by sanitizing the argument of the 'clearcpuid=' command-line option" 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/cpu: Fix bootup crashes by sanitizing the argument of the 'clearcpuid=' command-line option

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-cpu-fix-bootup-crashes-by-sanitizing-the-argument-of-the-clearcpuid-command-line-option.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: Lukasz Odzioba <[email protected]>
Date: Wed, 28 Dec 2016 14:55:40 +0100
Subject: x86/cpu: Fix bootup crashes by sanitizing the argument of the 'clearcpuid=' command-line option

From: Lukasz Odzioba <[email protected]>

commit dd853fd216d1485ed3045ff772079cc8689a9a4a upstream.

A negative number can be specified in the cmdline which will be used as setup_clear_cpu_cap() argument. With that we can clear/set some bit in memory predceeding boot_cpu_data/cpu_caps_cleared which may cause kernel to misbehave. This patch adds lower bound check to setup_disablecpuid().

Boris Petkov reproduced a crash:

  [    1.234575] BUG: unable to handle kernel paging request at ffffffff858bd540
  [    1.236535] IP: memcpy_erms+0x6/0x10

---
 arch/x86/kernel/cpu/common.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -1129,7 +1129,7 @@ static __init int setup_disablecpuid(cha
 {
 	int bit;
 
-	if (get_option(&arg, &bit) && bit < NCAPINTS*32)
+	if (get_option(&arg, &bit) && bit >= 0 && bit < NCAPINTS * 32)
 		setup_clear_cpu_cap(bit);
 	else
 		return 0;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/x86-cpu-fix-bootup-crashes-by-sanitizing-the-argument-of-the-clearcpuid-command-line-option.patch