[edk2-devel] [PATCH 1/4] OvmfPkg/VirtNorFlashDxe: fix shadowbuffer reads

["Gerd Hoffmann" <kraxel@redhat.com>]

In some cases (specifically when the flash update region is
small but crosses a multiple of P30_MAX_BUFFER_SIZE_IN_BYTES)
NorFlashWriteSingleBlock reads only one instead of two
P30_MAX_BUFFER_SIZE_IN_BYTES blocks into the shadow buffer.

That leads to random crap being written to the second block,
which in turn can corrupt both the variable store and the
FTW work space.  One observed corruption pattern is finding
0xaf (aka PcdDebugClearMemoryValue) right after the last
entry in the FTW log.  This should have been 0xff.

This patch fixes the calculation.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
index 1afd60ce66eb..cdc809d75e3d 100644
--- a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
+++ b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
@@ -566,7 +566,7 @@ NorFlashWriteSingleBlock (
                Instance,
                Lba,
                Offset & ~BOUNDARY_OF_32_WORDS,
-               (*NumBytes | BOUNDARY_OF_32_WORDS) + 1,
+               (((Offset & BOUNDARY_OF_32_WORDS) + *NumBytes) | BOUNDARY_OF_32_WORDS) + 1,
                Instance->ShadowBuffer
                );
     if (EFI_ERROR (Status)) {
-- 
2.43.0



-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#113717): https://edk2.groups.io/g/devel/message/113717
Mute This Topic: https://groups.io/mt/103680932/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-