image: Add support for signing of FIT configurations

While signing images is useful, it does not provide complete protection
against several types of attack. For example, it it possible to create a
FIT with the same signed images, but with the configuration changed such
that a different one is selected (mix and match attack). It is also possible
to substitute a signed image from an older FIT version into a newer FIT
(roll-back attack).

Add support for signing of FIT configurations using the libfdt's region
support.

Please see doc/uImage.FIT/signature.txt for more information.

Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 230 insertions, 1 deletions

diff --git a/common/image-sig.c b/common/image-sig.c
index 9928bfceca..5d907cfc42 100644
--- a/common/image-sig.c
+++ b/common/image-sig.c
@@ -25,10 +25,11 @@
 #include <malloc.h>
 DECLARE_GLOBAL_DATA_PTR;
 #endif /* !USE_HOSTCC*/
-#include <errno.h>
 #include <image.h>
 #include <rsa.h>
 
+#define IMAGE_MAX_HASHED_NODES		100
+
 struct image_sig_algo image_sig_algos[] = {
 	{
 		"sha1,rsa2048",
@@ -50,6 +51,50 @@ struct image_sig_algo *image_get_sig_algo(const char *name)
 	return NULL;
 }
 
+/**
+ * fit_region_make_list() - Make a list of image regions
+ *
+ * Given a list of fdt_regions, create a list of image_regions. This is a
+ * simple conversion routine since the FDT and image code use different
+ * structures.
+ *
+ * @fit: FIT image
+ * @fdt_regions: Pointer to FDT regions
+ * @count: Number of FDT regions
+ * @region: Pointer to image regions, which must hold @count records. If
+ * region is NULL, then (except for an SPL build) the array will be
+ * allocated.
+ * @return: Pointer to image regions
+ */
+struct image_region *fit_region_make_list(const void *fit,
+		struct fdt_region *fdt_regions, int count,
+		struct image_region *region)
+{
+	int i;
+
+	debug("Hash regions:\n");
+	debug("%10s %10s\n", "Offset", "Size");
+
+	/*
+	 * Use malloc() except in SPL (to save code size). In SPL the caller
+	 * must allocate the array.
+	 */
+#ifndef CONFIG_SPL_BUILD
+	if (!region)
+		region = calloc(sizeof(*region), count);
+#endif
+	if (!region)
+		return NULL;
+	for (i = 0; i < count; i++) {
+		debug("%10x %10x\n", fdt_regions[i].offset,
+		      fdt_regions[i].size);
+		region[i].data = fit + fdt_regions[i].offset;
+		region[i].size = fdt_regions[i].size;
+	}
+
+	return region;
+}
+
 static int fit_image_setup_verify(struct image_sign_info *info,
 		const void *fit, int noffset, int required_keynode,
 		char **err_msgp)
@@ -191,3 +236,187 @@ int fit_image_verify_required_sigs(const void *fit, int image_noffset,
 
 	return 0;
 }
+
+int fit_config_check_sig(const void *fit, int noffset, int required_keynode,
+			 char **err_msgp)
+{
+	char * const exc_prop[] = {"data"};
+	const char *prop, *end, *name;
+	struct image_sign_info info;
+	const uint32_t *strings;
+	uint8_t *fit_value;
+	int fit_value_len;
+	int max_regions;
+	int i, prop_len;
+	char path[200];
+	int count;
+
+	debug("%s: fdt=%p, conf='%s', sig='%s'\n", __func__, gd_fdt_blob(),
+	      fit_get_name(fit, noffset, NULL),
+	      fit_get_name(gd_fdt_blob(), required_keynode, NULL));
+	*err_msgp = NULL;
+	if (fit_image_setup_verify(&info, fit, noffset, required_keynode,
+				   err_msgp))
+		return -1;
+
+	if (fit_image_hash_get_value(fit, noffset, &fit_value,
+				     &fit_value_len)) {
+		*err_msgp = "Can't get hash value property";
+		return -1;
+	}
+
+	/* Count the number of strings in the property */
+	prop = fdt_getprop(fit, noffset, "hashed-nodes", &prop_len);
+	end = prop ? prop + prop_len : prop;
+	for (name = prop, count = 0; name < end; name++)
+		if (!*name)
+			count++;
+	if (!count) {
+		*err_msgp = "Can't get hashed-nodes property";
+		return -1;
+	}
+
+	/* Add a sanity check here since we are using the stack */
+	if (count > IMAGE_MAX_HASHED_NODES) {
+		*err_msgp = "Number of hashed nodes exceeds maximum";
+		return -1;
+	}
+
+	/* Create a list of node names from those strings */
+	char *node_inc[count];
+
+	debug("Hash nodes (%d):\n", count);
+	for (name = prop, i = 0; name < end; name += strlen(name) + 1, i++) {
+		debug("   '%s'\n", name);
+		node_inc[i] = (char *)name;
+	}
+
+	/*
+	 * Each node can generate one region for each sub-node. Allow for
+	 * 7 sub-nodes (hash@1, signature@1, etc.) and some extra.
+	 */
+	max_regions = 20 + count * 7;
+	struct fdt_region fdt_regions[max_regions];
+
+	/* Get a list of regions to hash */
+	count = fdt_find_regions(fit, node_inc, count,
+			exc_prop, ARRAY_SIZE(exc_prop),
+			fdt_regions, max_regions - 1,
+			path, sizeof(path), 0);
+	if (count < 0) {
+		*err_msgp = "Failed to hash configuration";
+		return -1;
+	}
+	if (count == 0) {
+		*err_msgp = "No data to hash";
+		return -1;
+	}
+	if (count >= max_regions - 1) {
+		*err_msgp = "Too many hash regions";
+		return -1;
+	}
+
+	/* Add the strings */
+	strings = fdt_getprop(fit, noffset, "hashed-strings", NULL);
+	if (strings) {
+		fdt_regions[count].offset = fdt_off_dt_strings(fit) +
+				fdt32_to_cpu(strings[0]);
+		fdt_regions[count].size = fdt32_to_cpu(strings[1]);
+		count++;
+	}
+
+	/* Allocate the region list on the stack */
+	struct image_region region[count];
+
+	fit_region_make_list(fit, fdt_regions, count, region);
+	if (info.algo->verify(&info, region, count, fit_value,
+			      fit_value_len)) {
+		*err_msgp = "Verification failed";
+		return -1;
+	}
+
+	return 0;
+}
+
+static int fit_config_verify_sig(const void *fit, int conf_noffset,
+		const void *sig_blob, int sig_offset)
+{
+	int noffset;
+	char *err_msg = "";
+	int verified = 0;
+	int ret;
+
+	/* Process all hash subnodes of the component conf node */
+	for (noffset = fdt_first_subnode(fit, conf_noffset);
+	     noffset >= 0;
+	     noffset = fdt_next_subnode(fit, noffset)) {
+		const char *name = fit_get_name(fit, noffset, NULL);
+
+		if (!strncmp(name, FIT_SIG_NODENAME,
+			     strlen(FIT_SIG_NODENAME))) {
+			ret = fit_config_check_sig(fit, noffset, sig_offset,
+						   &err_msg);
+			if (ret) {
+				puts("- ");
+			} else {
+				puts("+ ");
+				verified = 1;
+				break;
+			}
+		}
+	}
+
+	if (noffset == -FDT_ERR_TRUNCATED || noffset == -FDT_ERR_BADSTRUCTURE) {
+		err_msg = "Corrupted or truncated tree";
+		goto error;
+	}
+
+	return verified ? 0 : -EPERM;
+
+error:
+	printf(" error!\n%s for '%s' hash node in '%s' config node\n",
+	       err_msg, fit_get_name(fit, noffset, NULL),
+	       fit_get_name(fit, conf_noffset, NULL));
+	return -1;
+}
+
+int fit_config_verify_required_sigs(const void *fit, int conf_noffset,
+		const void *sig_blob)
+{
+	int noffset;
+	int sig_node;
+
+	/* Work out what we need to verify */
+	sig_node = fdt_subnode_offset(sig_blob, 0, FIT_SIG_NODENAME);
+	if (sig_node < 0) {
+		debug("%s: No signature node found: %s\n", __func__,
+		      fdt_strerror(sig_node));
+		return 0;
+	}
+
+	for (noffset = fdt_first_subnode(sig_blob, sig_node);
+	     noffset >= 0;
+	     noffset = fdt_next_subnode(sig_blob, noffset)) {
+		const char *required;
+		int ret;
+
+		required = fdt_getprop(sig_blob, noffset, "required", NULL);
+		if (!required || strcmp(required, "conf"))
+			continue;
+		ret = fit_config_verify_sig(fit, conf_noffset, sig_blob,
+					    noffset);
+		if (ret) {
+			printf("Failed to verify required signature '%s'\n",
+			       fit_get_name(sig_blob, noffset, NULL));
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+int fit_config_verify(const void *fit, int conf_noffset)
+{
+	return !fit_config_verify_required_sigs(fit, conf_noffset,
+						gd_fdt_blob());
+}