mkimage: Add -r option to specify keys that must be verified

Normally, multiple public keys can be provided and U-Boot is not
required to use all of them for verification. This is because some
images may not be signed, or may be optionally signed.

But we still need a mechanism to determine when a key must be used.
This feature cannot be implemented in the FIT itself, since anyone
could change it to mark a key as optional. The requirement for
key verification must go in with the public keys, in a place that
is protected from modification.

Add a -r option which tells mkimage to mark all keys that it uses
for signing as 'required'.

If some keys are optional and some are required, run mkimage several
times (perhaps with different key directories if some keys are very
secret) using the -F flag to update an existing FIT.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>

doc/mkimage.1

@@ -133,6 +133,12 @@ the corresponding public key is written into this file for for run-time
 verification. Typically the file here is the device tree binary used by
 CONFIG_OF_CONTROL in U-Boot.
 
+.TP
+.BI "\-r
+Specifies that keys used to sign the FIT are required. This means that they
+must be verified for the image to boot. Without this option, the verification
+will be optional (useful for testing but not for release).
+
 .SH EXAMPLES
 
 List image information:

tools/fit_image.c

@@ -152,10 +152,11 @@ static int fit_handle_file (struct mkimage_params *params)
 		goto err_mmap;
 
 	/* set hashes for images in the blob */
-	if (fit_add_verification_data(params->keydir, dest_blob, ptr,
-				      params->comment, 0)) {
-		fprintf (stderr, "%s Can't add hashes to FIT blob",
-			 params->cmdname);
+	if (fit_add_verification_data(params->keydir,
+				      dest_blob, ptr, params->comment,
+				      params->require_keys)) {
+		fprintf(stderr, "%s Can't add hashes to FIT blob\n",
+			params->cmdname);
 		goto err_add_hashes;
 	}
 

tools/mkimage.c

@@ -270,6 +270,9 @@ main (int argc, char **argv)
 					usage ();
 				params.imagename = *++argv;
 				goto NXTARG;
+			case 'r':
+				params.require_keys = 1;
+				break;
 			case 'R':
 				if (--argc <= 0)
 					usage();
@@ -645,11 +648,12 @@ usage ()
 	fprintf(stderr, "          -D => set options for device tree compiler\n"
 			"          -f => input filename for FIT source\n");
 #ifdef CONFIG_FIT_SIGNATURE
-	fprintf(stderr, "Signing / verified boot options: [-k keydir] [-K dtb] [ -c <comment>]\n"
+	fprintf(stderr, "Signing / verified boot options: [-k keydir] [-K dtb] [ -c <comment>] [-r]\n"
 			"          -k => set directory containing private keys\n"
 			"          -K => write public keys to this .dtb file\n"
 			"          -c => add comment in signature node\n"
-			"          -F => re-sign existing FIT image\n");
+			"          -F => re-sign existing FIT image\n"
+			"          -r => mark keys used as 'required' in dtb\n");
 #else
 	fprintf(stderr, "Signing / verified boot not supported (CONFIG_FIT_SIGNATURE undefined)\n");
 #endif

tools/mkimage.h

@@ -90,6 +90,7 @@ struct mkimage_params {
 	const char *keydir;	/* Directory holding private keys */
 	const char *keydest;	/* Destination .dtb for public key */
 	const char *comment;	/* Comment to add to signature node */
+	int require_keys;	/* 1 to mark signing keys as 'required' */
 };
 
 /*