Security: Make sure not to overflow the in memory version of the GBB

This change plumbs the size of the GBB specified in the device tree to the
functions that read it from the flash into memory, and adds checks to those
functions to make sure they don't spill out of the in memory GBB. From a
security standpoint this is a largely theoretical problem since the GBB is
in the read only portion of flash and if that can be modified the machine
is totally compromised, but it's possible somehow an attacker could force
vboot to read the GBB from the wrong place. From a practical perspective
it's not a bad idea to check this to avoid accidental memory corruption.

BUG=chromium-os:24223
TEST=Built and booted on Lumpy. Built for Kaen.

Change-Id: I4f33552f9d27321e73659520b08be52d775a6a9b
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/13228
Reviewed-by: Che-Liang Chiou <clchiou@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>

1 files changed, 31 insertions, 4 deletions

diff --git a/lib/chromeos/gbb.c b/lib/chromeos/gbb.c
index 25d5741318..b2ab343b6f 100644
--- a/lib/chromeos/gbb.c
+++ b/lib/chromeos/gbb.c
@@ -16,16 +16,28 @@
 
 #define PREFIX "gbb: "
 
-int gbb_init(read_buf_type gbb, firmware_storage_t *file, uint32_t gbb_offset)
+int gbb_init(read_buf_type gbb, firmware_storage_t *file, uint32_t gbb_offset,
+	     size_t gbb_size)
 {
 #ifndef CONFIG_HARDWARE_MAPPED_SPI
 	GoogleBinaryBlockHeader *gbbh = (GoogleBinaryBlockHeader *)gbb;
+	uint32_t hwid_end;
+	uint32_t rootkey_end;
 
 	if (file->read(file, gbb_offset, sizeof(*gbbh), gbbh)) {
 		VBDEBUG(PREFIX "failed to read GBB header\n");
 		return 1;
 	}
 
+	hwid_end = gbbh->hwid_offset + gbbh->hwid_size;
+	rootkey_end = gbbh->rootkey_offset + gbbh->rootkey_size;
+	if (hwid_end < gbbh->hwid_offset || hwid_end >= gbb_size ||
+			rootkey_end < gbbh->rootkey_offset ||
+			rootkey_end >= gbb_size) {
+		VBDEBUG(PREFIX "invalid gbb header entries");
+		return 1;
+	}
+
 	if (file->read(file, gbb_offset + gbbh->hwid_offset,
 				gbbh->hwid_size,
 				gbb + gbbh->hwid_offset)) {
@@ -40,6 +52,7 @@ int gbb_init(read_buf_type gbb, firmware_storage_t *file, uint32_t gbb_offset)
 		return 1;
 	}
 #else
+	/* No data is actually moved in this case so no bounds checks. */
 	if (file->read(file, gbb_offset,
 		       sizeof(GoogleBinaryBlockHeader), gbb)) {
 		VBDEBUG(PREFIX "failed to read GBB header\n");
@@ -51,9 +64,16 @@ int gbb_init(read_buf_type gbb, firmware_storage_t *file, uint32_t gbb_offset)
 }
 
 #ifndef CONFIG_HARDWARE_MAPPED_SPI
-int gbb_read_bmp_block(void *gbb, firmware_storage_t *file, uint32_t gbb_offset)
+int gbb_read_bmp_block(void *gbb, firmware_storage_t *file, uint32_t gbb_offset,
+		       size_t gbb_size)
 {
 	GoogleBinaryBlockHeader *gbbh = (GoogleBinaryBlockHeader *)gbb;
+	uint32_t bmpfv_end = gbbh->bmpfv_offset + gbbh->bmpfv_size;
+
+	if (bmpfv_end < gbbh->bmpfv_offset || bmpfv_end >= gbb_size) {
+		VBDEBUG(PREFIX "invalid gbb header entries");
+		return 1;
+	}
 
 	if (file->read(file, gbb_offset + gbbh->bmpfv_offset,
 				gbbh->bmpfv_size,
@@ -65,10 +85,17 @@ int gbb_read_bmp_block(void *gbb, firmware_storage_t *file, uint32_t gbb_offset)
 	return 0;
 }
 
-int gbb_read_recovery_key(void *gbb,
-		firmware_storage_t *file, uint32_t gbb_offset)
+int gbb_read_recovery_key(void *gbb, firmware_storage_t *file,
+			  uint32_t gbb_offset, size_t gbb_size)
 {
 	GoogleBinaryBlockHeader *gbbh = (GoogleBinaryBlockHeader *)gbb;
+	uint32_t rkey_end = gbbh->recovery_key_offset +
+		gbbh->recovery_key_size;
+
+	if (rkey_end < gbbh->recovery_key_offset || rkey_end >= gbb_size) {
+		VBDEBUG(PREFIX "invalid gbb header entries");
+		return 1;
+	}
 
 	if (file->read(file, gbb_offset + gbbh->recovery_key_offset,
 				gbbh->recovery_key_size,