[ 83/85] x86, microcode, AMD: Fix broken ucode patch size check

From: Greg Kroah-Hartman
Date: Wed Sep 12 2012 - 19:57:07 EST

From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>

3.4-stable review patch. If anyone has any objections, please let me know.


From: Andreas Herrmann <andreas.herrmann3@xxxxxxx>

commit 36bf50d7697be18c6bfd0401e037df10bff1e573 upstream.

This issue was recently observed on an AMD C-50 CPU where a patch of
maximum size was applied.

Commit be62adb49294 ("x86, microcode, AMD: Simplify ucode verification")
added current_size in get_matching_microcode(). This is calculated as
size of the ucode patch + 8 (ie. size of the header). Later this is
compared against the maximum possible ucode patch size for a CPU family.
And of course this fails if the patch has already maximum size.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@xxxxxxx>
Signed-off-by: Borislav Petkov <borislav.petkov@xxxxxxx>
Link: http://lkml.kernel.org/r/1344361461-10076-1-git-send-email-bp@xxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/x86/kernel/microcode_amd.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/microcode_amd.c
+++ b/arch/x86/kernel/microcode_amd.c
@@ -143,11 +143,12 @@ static int get_matching_microcode(int cp
unsigned int *current_size)
struct microcode_header_amd *mc_hdr;
- unsigned int actual_size;
+ unsigned int actual_size, patch_size;
u16 equiv_cpu_id;

/* size of the current patch we're staring at */
- *current_size = *(u32 *)(ucode_ptr + 4) + SECTION_HDR_SIZE;
+ patch_size = *(u32 *)(ucode_ptr + 4);
+ *current_size = patch_size + SECTION_HDR_SIZE;

equiv_cpu_id = find_equiv_id();
if (!equiv_cpu_id)
@@ -174,7 +175,7 @@ static int get_matching_microcode(int cp
* now that the header looks sane, verify its size
- actual_size = verify_ucode_size(cpu, *current_size, leftover_size);
+ actual_size = verify_ucode_size(cpu, patch_size, leftover_size);
if (!actual_size)
return 0;

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