brescue.sh: account for HW cryptolib header in the imagestabilize-quickfix-14695.187.B-cr50_stabstabilize-quickfix-14695.124.B-cr50_stabstabilize-14695.85.B-cr50_stabstabilize-14695.107.B-cr50_stabrelease-R102-14695.B-cr50_stab

Adding the encrypted cryptolib header to the RO created another match
for the header magic pattern of 'fd ff ff ff'.

One of the distinct properties of the fake header is filling up the
signature field with 0x53 bytes, let's use this to filter out the fake
header when looking for the RW.

BUG=b:217564005,b:228839885
TEST=successfully processed Ti50 image with HW cryptolib included.

Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Change-Id: I83e4f7ad90ba1030ec4134db00485f10dc2fcdee
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3561025
Reviewed-by: Andrew Luo <aluo@chromium.org>
Reviewed-by: Edward Hill <ecgh@chromium.org>
Commit-Queue: Edward Hill <ecgh@chromium.org>
Reviewed-by: Vadim Sukhomlinov <sukhomlinov@chromium.org>
Commit-Queue: Vadim Sukhomlinov <sukhomlinov@chromium.org>
Tested-by: Vadim Sukhomlinov <sukhomlinov@chromium.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/util/brescue.sh b/util/brescue.sh
index 16bf9cfbec..87fcac91d9 100755
--- a/util/brescue.sh
+++ b/util/brescue.sh
@@ -64,8 +64,11 @@ rw_offset() {
   local base
 
   src="$1"
+  # The second grep term filters out the 'fake' cryptolib header, which does
+  # not contain a valid signature, the signature field is filled with SSSSS
+  # (0x53...).
   base=$(/usr/bin/od -Ax -t x1 -v "${src}" |
-    grep -E '^....00 fd ff ff ff' |
+    grep -E '^....00 fd ff ff ff' | grep -v '00 fd ff ff ff 53 53 53' |
     head -2 |
     tail -1 |
     sed 's/ .*//')