chromeos: vpd: Avoid reading uninitialized VPDs

This patch adds a check to the VPD parsing code to avoid reading the
whole thing if the first byte ('type' of the first VPD entry) is 0x00
or 0xff. These values match the TERMINATOR and IMPLICIT_TERMINATOR types
which should never occur as the first entry, so this usually means that
the VPD FMAP section has simply never been initialized correctly. This
early abort avoids wasting time to read the whole section from SPI flash
(which we'd otherwise have to since we're not going to find a Google VPD
2.0 header either).

BRANCH=None
BUG=None
TEST=Booted Oak, confirmed that VPD read times dropped from 100ms to
1.5ms.

Change-Id: I9fc473e06440aef4e1023238fb9e53d45097ee9d
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 20a726237e03941ad626a6146700170a45ee7720
Original-Change-Id: I09bfec3c24d24214fa4e9180878b58d00454f399
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/322897
Original-Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: https://review.coreboot.org/13467
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/src/vendorcode/google/chromeos/cros_vpd.c b/src/vendorcode/google/chromeos/cros_vpd.c
index e826d36218..d0e2cc1ef9 100644
--- a/src/vendorcode/google/chromeos/cros_vpd.c
+++ b/src/vendorcode/google/chromeos/cros_vpd.c
@@ -65,11 +65,21 @@ static int32_t get_vpd_size(const char *fmap_name, int32_t *base)
 	}
 
 	/* Try if we can find a google_vpd_info, otherwise read whole VPD. */
-	if (rdev_readat(&vpd, &info, *base, sizeof(info)) == sizeof(info) &&
-	    memcmp(info.header.magic, VPD_INFO_MAGIC, sizeof(info.header.magic))
+	if (rdev_readat(&vpd, &info, *base, sizeof(info)) != sizeof(info)) {
+		printk(BIOS_ERR, "ERROR: Failed to read %s header.\n",
+		       fmap_name);
+		return 0;
+	}
+
+	if (memcmp(info.header.magic, VPD_INFO_MAGIC, sizeof(info.header.magic))
 	    == 0 && size >= info.size + sizeof(info)) {
 		*base += sizeof(info);
 		size = info.size;
+	} else if (info.header.tlv.type == VPD_TYPE_TERMINATOR ||
+		   info.header.tlv.type == VPD_TYPE_IMPLICIT_TERMINATOR) {
+		printk(BIOS_WARNING, "WARNING: %s is uninitialized or empty.\n",
+		       fmap_name);
+		size = 0;
 	} else {
 		size -= GOOGLE_VPD_2_0_OFFSET;
 	}