serial recovery: image list not working with encrypted images and single slot

[wag-thom]

Problem

In serial recovery, the image list command does not list encrypted images if only one slot is used (MCUBOOT_SINGLE_APPLICATION_SLOT)

> mcumgr -c my_conn image list
Images:
Split status: N/A (0)

Cause

A similar Issue #1753 was fixed by #1747, but the added check && MUST_DECRYPT(...) does not work for single slot applications.

if (IS_ENCRYPTED(&hdr) && MUST_DECRYPT(fap, image_index, &hdr)) {
    FIH_CALL(boot_image_validate_encrypted, fih_rc, fap,
             &hdr, tmpbuf, sizeof(tmpbuf));
} else {
...

boot_serial.c @ L297

The MUST_DECRYPT() macro seems to determine if decryption is necessary, by checking if the image is in the second slot. Since we do not have a second slot in a single slot application, the macro FLASH_AREA_IMAGE_SECONDARY() will return the index of the first slot and is therefore always true.

#define MUST_DECRYPT(fap, idx, hdr) \
    (flash_area_get_id(fap) == FLASH_AREA_IMAGE_SECONDARY(idx) && IS_ENCRYPTED(hdr))

image.h @ L160

Possible Fix

A possible fix could be to only use MUST_DECRYPT if we are not in a single slot setup:

if (IS_ENCRYPTED(&hdr) && (MUST_DECRYPT(fap, image_index, &hdr) && !MCUBOOT_SINGLE_APPLICATION_SLOT)) {
...

On the other hand, I do not exactly understand why the encrypted-flags in the image header are set at that point. The image in this scenario was decrypted in-place right after it was uploaded by serial recovery. Shouldn't the header also get updated with cleared encrypted-flags once it is decrypted? I do not exactly know how MCUboot is intended to work, so maybe that is intentional for some reason I do not see...

[thedjnK]

I remember this issue being fixed, what commit of mcuboot are you using? Indeed seems broken

[nordicjm]

Fix: #1865