[U-Boot] [RFC PATCH 38/44] mkimage: Add -F option to modify an existing .fit file

[Simon Glass]

When signing images it is sometimes necessary to sign with different keys
at different times, or make the signer entirely separate from the FIT
creation to avoid needing the private keys to be publicly available in
the system.

Add a -F option so that key signing can be a separate step, and possibly
done multiple times as different keys are avaiable.

Signed-off-by: Simon Glass <sjg at chromium.org>
---
 doc/mkimage.1     |   20 ++++++++++++++++++++
 tools/fit_image.c |   18 ++++++++++++------
 tools/mkimage.c   |    6 ++++--
 3 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/doc/mkimage.1 b/doc/mkimage.1
index 8185ff5..f9c733a 100644
--- a/doc/mkimage.1
+++ b/doc/mkimage.1
@@ -10,6 +10,9 @@ mkimage \- Generate image for U-Boot
 .RB [\fIoptions\fP] " \-f [" "image tree source file" "]" " [" "uimage file name" "]"
 
 .B mkimage
+.RB [\fIoptions\fP] " \-F [" "uimage file name" "]"
+
+.B mkimage
 .RB [\fIoptions\fP] " (legacy mode)"
 
 .SH "DESCRIPTION"
@@ -104,6 +107,13 @@ Image tree source file that describes the structure and contents of the
 FIT image.
 
 .TP
+.BI "\-F"
+Indicates that an existing FIT image should be modified. No dtc
+compilation is performed and the -f flag should not be given.
+This can be used to sign images with additional keys after initial image
+creation.
+
+.TP
 .BI "\-k [" "key_directory" "]"
 Specifies the directory containing keys to use for signing. This directory
 should contain a private key file <name>.key for use with signing and a
@@ -144,6 +154,16 @@ skipping those for which keys cannot be found. Also add a comment.
 -c "Kernel 3.8 image for production devices" kernel.itb
 .fi
 
+.P
+Update an existing FIT image, signing it with additional keys.
+Add corresponding public keys into u-boot.dtb. This will resign all images
+with keys that are available in the new directory. Images that request signing
+with unavailable keys are skipped.
+.nf
+.B mkimage -F -k /secret/signing-keys -K u-boot.dtb \\\\
+-c "Kernel 3.8 image for production devices" kernel.itb
+.fi
+
 .SH HOMEPAGE
 http://www.denx.de/wiki/U-Boot/WebHome
 .PP
diff --git a/tools/fit_image.c b/tools/fit_image.c
index 306298a..835d2fb 100644
--- a/tools/fit_image.c
+++ b/tools/fit_image.c
@@ -124,10 +124,16 @@ static int fit_handle_file (struct mkimage_params *params)
 	}
 	sprintf (tmpfile, "%s%s", params->imagefile, MKIMAGE_TMPFILE_SUFFIX);
 
-	/* dtc -I dts -O dtb -p 500 datafile > tmpfile */
-	sprintf (cmd, "%s %s %s > %s",
-		MKIMAGE_DTC, params->dtc, params->datafile, tmpfile);
-	debug ("Trying to execute \"%s\"\n", cmd);
+	/* We either compile the source file, or use the existing FIT image */
+	if (params->datafile) {
+		/* dtc -I dts -O dtb -p 500 datafile > tmpfile */
+		snprintf(cmd, sizeof(cmd), "%s %s %s > %s",
+			MKIMAGE_DTC, params->dtc, params->datafile, tmpfile);
+		debug("Trying to execute \"%s\"\n", cmd);
+	} else {
+		snprintf(cmd, sizeof(cmd), "cp %s %s",
+			params->imagefile, tmpfile);
+	}
 	if (system (cmd) == -1) {
 		fprintf (stderr, "%s: system(%s) failed: %s\n",
 				params->cmdname, cmd, strerror(errno));
@@ -153,8 +159,8 @@ static int fit_handle_file (struct mkimage_params *params)
 		goto err_add_hashes;
 	}
 
-	/* add a timestamp at offset 0 i.e., root  */
-	if (fit_set_timestamp (ptr, 0, sbuf.st_mtime)) {
+	/* for first image creation, add a timestamp at offset 0 i.e., root  */
+	if (params->datafile && fit_set_timestamp(ptr, 0, sbuf.st_mtime)) {
 		fprintf (stderr, "%s: Can't add image timestamp\n",
 				params->cmdname);
 		goto err_add_timestamp;
diff --git a/tools/mkimage.c b/tools/mkimage.c
index 30a5a06..99787d9 100644
--- a/tools/mkimage.c
+++ b/tools/mkimage.c
@@ -240,12 +240,14 @@ main (int argc, char **argv)
 			case 'f':
 				if (--argc <= 0)
 					usage ();
+				params.datafile = *++argv;
+				/* no break */
+			case 'F':
 				/*
 				 * The flattened image tree (FIT) format
 				 * requires a flattened device tree image type
 				 */
 				params.type = IH_TYPE_FLATDT;
-				params.datafile = *++argv;
 				params.fflag = 1;
 				goto NXTARG;
 			case 'k':
@@ -634,7 +636,7 @@ usage ()
 			 "          -x ==> set XIP (execute in place)\n",
 		params.cmdname);
 	fprintf(stderr, "       %s [-k keydir] [-K dtb] [-D dtc_options]"
-			" -f fit-image.its fit-image\n", params.cmdname);
+			" [-f fit-image.its|-F] fit-image\n", params.cmdname);
 	fprintf (stderr, "       %s -V ==> print version information and exit\n",
 		params.cmdname);
 
-- 
1.7.7.3