brcm2708: implement sysupgrade image check

Implement a crude but functioning sysupgrade image check for the
Raspberry Pi. The code only checks if the master boot record boot
signature (0x55aa) is present in the first 512-bytes at the correct
location. This can prevent the odd bricking of a system when flashing
the wrong file.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>

diff --git a/target/linux/brcm2708/base-files/lib/upgrade/platform.sh b/target/linux/brcm2708/base-files/lib/upgrade/platform.sh
index 1d4b694574c5acbc5bcac39cf3f2094026058ac5..2f2aeb098e29b084273845aea7d5ee145d2082aa 100644 (file)
--- a/target/linux/brcm2708/base-files/lib/upgrade/platform.sh
+++ b/target/linux/brcm2708/base-files/lib/upgrade/platform.sh
@@ -1,5 +1,19 @@
+get_magic_at() {
+       local file="$1"
+       local pos="$2"
+       get_image "$file" | dd bs=1 count=2 skip="$pos" 2>/dev/null | hexdump -v -n 2 -e '1/1 "%02x"'
+}
+
 platform_check_image() {
-       # i know no way to verify the image
+       local file="$1"
+       local magic
+
+       magic=$(get_magic_at "$file" 510)
+       [ "$magic" != "55aa" ] && {
+               echo "Failed to verify MBR boot signature."
+               return 1
+       }
+
        return 0;
 }