[tip:x86/urgent] x86/microcode/intel: Guard against stack overflow in the loader

From: tip-bot for Quentin Casasnovas
Date: Thu Feb 19 2015 - 14:28:38 EST

Commit-ID: f84598bd7c851f8b0bf8cd0d7c3be0d73c432ff4
Gitweb: http://git.kernel.org/tip/f84598bd7c851f8b0bf8cd0d7c3be0d73c432ff4
Author: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
AuthorDate: Tue, 3 Feb 2015 13:00:22 +0100
Committer: Borislav Petkov <bp@xxxxxxx>
CommitDate: Thu, 19 Feb 2015 12:41:37 +0100

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

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@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1422964824-22056-1-git-send-email-quentin.casasnovas@xxxxxxxxxx
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
arch/x86/kernel/cpu/microcode/intel_early.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel_early.c b/arch/x86/kernel/cpu/microcode/intel_early.c
index ec9df6f..5e109a3 100644
--- a/arch/x86/kernel/cpu/microcode/intel_early.c
+++ b/arch/x86/kernel/cpu/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);
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