bootutil: loader: Verify image header before checking image

Changes the order of operations to validate the image header
before checking the image, it does not make sense to check the
image if the header itself is invalid

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

boot/bootutil/src/loader.c

@@ -1028,13 +1028,17 @@ boot_validate_slot(struct boot_loader_state *state, int slot,
  }
  }
 #endif
- BOOT_HOOK_CALL_FIH(boot_image_check_hook, FIH_BOOT_HOOK_REGULAR,
- fih_rc, BOOT_CURR_IMG(state), slot);
- if (FIH_EQ(fih_rc, FIH_BOOT_HOOK_REGULAR))
- {
- FIH_CALL(boot_image_check, fih_rc, state, hdr, fap, bs);
- }
- if (!boot_is_header_valid(hdr, fap, state) || FIH_NOT_EQ(fih_rc, FIH_SUCCESS)) {
+ if (!boot_is_header_valid(hdr, fap, state)) {
+ fih_rc = FIH_FAILURE;
+ } else {
+ BOOT_HOOK_CALL_FIH(boot_image_check_hook, FIH_BOOT_HOOK_REGULAR,
+ fih_rc, BOOT_CURR_IMG(state), slot);
+ if (FIH_EQ(fih_rc, FIH_BOOT_HOOK_REGULAR))
+ {
+ FIH_CALL(boot_image_check, fih_rc, state, hdr, fap, bs);
+ }
+ }
+ if (FIH_NOT_EQ(fih_rc, FIH_SUCCESS)) {
  if ((slot != BOOT_PRIMARY_SLOT) || ARE_SLOTS_EQUIVALENT()) {
  flash_area_erase(fap, 0, flash_area_get_size(fap));
  /* Image is invalid, erase it to prevent further unnecessary