lib: rsa: add documentation to padding_pss_verify to document limitations

padding_pss_verify only works with the default pss salt setting of -2
(length to be automatically determined based on the PSS block structure)
not -1 (salt length set to the maximum permissible value), which makes
verifications of signatures with that saltlen fail.

Until this gets implemented at least document this behaviour.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

diff --git a/lib/rsa/rsa-verify.c b/lib/rsa/rsa-verify.c
index 048f1ab7893389bbca1c2e5973343539cf62fc07..61d98e6e2d5ca7486fdd5aecd8f2d8dce80a3ad4 100644 (file)
--- a/lib/rsa/rsa-verify.c
+++ b/lib/rsa/rsa-verify.c
@@ -194,6 +194,19 @@ out:
        return ret;
 }
 
+/*
+ * padding_pss_verify() - verify the pss padding of a signature
+ *
+ * Only works with a rsa_pss_saltlen:-2 (default value) right now
+ * saltlen:-1 "set the salt length to the digest length" is currently
+ * not supported.
+ *
+ * @info:      Specifies key and FIT information
+ * @msg:       byte array of message, len equal to msg_len
+ * @msg_len:   Message length
+ * @hash:      Pointer to the expected hash
+ * @hash_len:  Length of the hash
+ */
 int padding_pss_verify(struct image_sign_info *info,
                       uint8_t *msg, int msg_len,
                       const uint8_t *hash, int hash_len)