[3.13.y-ckt stable] Patch "x86/microcode/intel: Guard against stack overflow in the loader" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    x86/microcode/intel: Guard against stack overflow in the loader

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 75c1b0a694b4bbaa43957951bd86b913d197f655 Mon Sep 17 00:00:00 2001
From: Quentin Casasnovas <quentin.casasnovas at oracle.com>
Date: Tue, 3 Feb 2015 13:00:22 +0100
Subject: x86/microcode/intel: Guard against stack overflow in the loader

commit f84598bd7c851f8b0bf8cd0d7c3be0d73c432ff4 upstream.

mc_saved_tmp is a static array allocated on the stack, we need to make
sure mc_saved_count stays within its bounds, otherwise we're overflowing
the stack in _save_mc(). A specially crafted microcode header could lead
to a kernel crash or potentially kernel execution.

Signed-off-by: Quentin Casasnovas <quentin.casasnovas at oracle.com>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: Fenghua Yu <fenghua.yu at intel.com>
Link: http://lkml.kernel.org/r/1422964824-22056-1-git-send-email-quentin.casasnovas@oracle.com
Signed-off-by: Borislav Petkov <bp at suse.de>
[ kamal: backport to 3.13-stable: applied to microcode_intel_early.c ]
Reference: CVE-2015-2666
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/kernel/microcode_intel_early.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/microcode_intel_early.c b/arch/x86/kernel/microcode_intel_early.c
index 1575deb..c44f7db 100644
--- a/arch/x86/kernel/microcode_intel_early.c
+++ b/arch/x86/kernel/microcode_intel_early.c
@@ -321,7 +321,7 @@ get_matching_model_microcode(int cpu, unsigned long start,
 	unsigned int mc_saved_count = mc_saved_data->mc_saved_count;
 	int i;

-	while (leftover) {
+	while (leftover && mc_saved_count < ARRAY_SIZE(mc_saved_tmp)) {
 		mc_header = (struct microcode_header_intel *)ucode_ptr;

 		mc_size = get_totalsize(mc_header);
--
1.9.1