Hi Daniele,

On Fri, 13 Sep 2019 at 09:50, Daniele Alessandrelli daniele.alessandrelli@gmail.com wrote:

Hi,

I was looking at the RSA image authentication code and I'm a bit puzzled by the following line of codes in lib/rsa/rsa-verify.c (https://gitlab.denx.de/u-boot/u-boot/blob/master/lib/rsa/rsa-verify.c#L440):

436 /* See if we must use a particular key */ 437 if (info->required_keynode != -1) { 438 ret = rsa_verify_with_keynode(info, hash, sig, sig_len, 439 info->required_keynode); 440 if (!ret) 441 return ret; 442 } 443 444 /* Look for a key that matches our hint */ 445 snprintf(name, sizeof(name), "key-%s", info->keyname); 446 node = fdt_subnode_offset(blob, sig_node, name); 447 ret = rsa_verify_with_keynode(info, hash, sig, sig_len, node); 448 if (!ret) 449 return ret;

If I understand it correctly, at Line 440 we check if verification with the required key succeeded and if so we return otherwise we continue, trying other keys.

Yes that's my understanding too.

Is that the intended behavior? Shouldn't the code return in any case (thus making the FIT verification process fail if the image couldn't be verified with the required key)? Or am I missing something?

Yes I think you are right. The documentation says:

- required: If present this indicates that the key must be verified for the image / configuration to be considered valid. Only required keys are normally verified by the FIT image booting algorithm. Valid values are "image" to force verification of all images, and "conf" to force verification of the selected configuration (which then relies on hashes in the images to verify those).

The test coverage does not handle that case at present, but it should.

Regards, Simon