boot: Add fit_config_get_hash_list() to build signed node list
authorSimon Glass <simon.glass@canonical.com>
Fri, 6 Mar 2026 01:20:09 +0000 (18:20 -0700)
committerAndreas Henriksson <andreas@fatal.se>
Tue, 23 Jun 2026 19:07:40 +0000 (21:07 +0200)
The hashed-nodes property in a FIT signature node lists which FDT paths
are included in the signature hash. It is intended as a hint so should
not be used for verification.

Add a function to build the node list from scratch by iterating the
configuration's image references. Skip properties known not to be image
references. For each image, collect the path plus all hash and cipher
subnodes.

Use the new function in fit_config_check_sig() instead of reading
'hashed-nodes'.

Update the test_vboot kernel@ test case: fit_check_sign now catches the
attack at signature-verification time (the @-suffixed node is hashed
instead of the real one, causing a mismatch) rather than at
fit_check_format() time.

Update the docs to cover this. The FIT spec can be updated separately.

Signed-off-by: Simon Glass <simon.glass@canonical.com>
Closes: https://lore.kernel.org/u-boot/20260302220937.3682128-1-trini@konsulko.com/
Reported-by: Apple Security Engineering and Architecture (SEAR)
Tested-by: Tom Rini <trini@konsulko.com>
(cherry picked from commit 2092322b31cc8b1f8c9e2e238d1043ae0637b241)

Gbp-Pq: Name CVE-2026-46728-2.patch

common/image-fit-sig.c

index 7c19ac6dc214d33e11f74bc16788ef8a2adc0fbd..ecbf3ec984b781ba5b18dccba5847ecfb635c9c1 100644 (file)
@@ -18,6 +18,7 @@ DECLARE_GLOBAL_DATA_PTR;
 #include <u-boot/rsa-checksum.h>
 
 #define IMAGE_MAX_HASHED_NODES         100
+#define FIT_MAX_HASH_PATH_BUF          4096
 
 #ifdef USE_HOSTCC
 void *host_blob;
@@ -239,6 +240,179 @@ int fit_image_verify_required_sigs(const void *fit, int image_noffset,
        return 0;
 }
 
+/**
+ * fit_config_add_hash() - Add hash nodes for one image to the node list
+ *
+ * Adds the image path, all its hash-* subnode paths, and its cipher
+ * subnode path (if present) to the packed buffer.
+ *
+ * @fit:               FIT blob
+ * @image_noffset:     Image node offset (e.g. /images/kernel-1)
+ * @node_inc:          Array of path pointers to fill
+ * @count:             Pointer to current count (updated on return)
+ * @max_nodes:         Maximum entries in @node_inc
+ * @buf:               Buffer for packed path strings
+ * @buf_used:          Pointer to bytes used in @buf (updated on return)
+ * @buf_len:           Total size of @buf
+ * Return: 0 on success, -ve on error
+ */
+static int fit_config_add_hash(const void *fit, int image_noffset,
+                              char **node_inc, int *count, int max_nodes,
+                              char *buf, int *buf_used, int buf_len)
+{
+       int noffset, hash_count, ret, len;
+
+       if (*count >= max_nodes)
+               return -ENOSPC;
+
+       ret = fdt_get_path(fit, image_noffset, buf + *buf_used,
+                          buf_len - *buf_used);
+       if (ret < 0)
+               return -ENOENT;
+       len = strlen(buf + *buf_used) + 1;
+       node_inc[(*count)++] = buf + *buf_used;
+       *buf_used += len;
+
+       /* Add all this image's hash subnodes */
+       hash_count = 0;
+       for (noffset = fdt_first_subnode(fit, image_noffset);
+            noffset >= 0;
+            noffset = fdt_next_subnode(fit, noffset)) {
+               const char *name = fit_get_name(fit, noffset, NULL);
+
+               if (strncmp(name, FIT_HASH_NODENAME,
+                           strlen(FIT_HASH_NODENAME)))
+                       continue;
+               if (*count >= max_nodes)
+                       return -ENOSPC;
+               ret = fdt_get_path(fit, noffset, buf + *buf_used,
+                                  buf_len - *buf_used);
+               if (ret < 0)
+                       return -ENOENT;
+               len = strlen(buf + *buf_used) + 1;
+               node_inc[(*count)++] = buf + *buf_used;
+               *buf_used += len;
+               hash_count++;
+       }
+
+       if (!hash_count) {
+               printf("No hash nodes in image '%s'\n",
+                      fdt_get_name(fit, image_noffset, NULL));
+               return -ENOMSG;
+       }
+
+       /* Add this image's cipher node if present */
+       noffset = fdt_subnode_offset(fit, image_noffset, FIT_CIPHER_NODENAME);
+       if (noffset != -FDT_ERR_NOTFOUND) {
+               if (noffset < 0)
+                       return -EIO;
+               if (*count >= max_nodes)
+                       return -ENOSPC;
+               ret = fdt_get_path(fit, noffset, buf + *buf_used,
+                                  buf_len - *buf_used);
+               if (ret < 0)
+                       return -ENOENT;
+               len = strlen(buf + *buf_used) + 1;
+               node_inc[(*count)++] = buf + *buf_used;
+               *buf_used += len;
+       }
+
+       return 0;
+}
+
+/**
+ * fit_config_get_hash_list() - Build the list of nodes to hash
+ *
+ * Works through every image referenced by the configuration and collects the
+ * node paths: root + config + all referenced images with their hash and
+ * cipher subnodes.
+ *
+ * Properties known not to be image references (description, compatible,
+ * default, load-only) are skipped, so any new image type is covered by default.
+ *
+ * @fit:       FIT blob
+ * @conf_noffset: Configuration node offset
+ * @node_inc:  Array to fill with path string pointers
+ * @max_nodes: Size of @node_inc array
+ * @buf:       Buffer for packed null-terminated path strings
+ * @buf_len:   Size of @buf
+ * Return: number of entries in @node_inc, or -ve on error
+ */
+static int fit_config_get_hash_list(const void *fit, int conf_noffset,
+                                   char **node_inc, int max_nodes,
+                                   char *buf, int buf_len)
+{
+       const char *conf_name;
+       int image_count;
+       int prop_offset;
+       int used = 0;
+       int count = 0;
+       int ret, len;
+
+       conf_name = fit_get_name(fit, conf_noffset, NULL);
+
+       /* Always include the root node and the configuration node */
+       if (max_nodes < 2)
+               return -ENOSPC;
+
+       len = 2;  /* "/" + nul */
+       if (len > buf_len)
+               return -ENOSPC;
+       strcpy(buf, "/");
+       node_inc[count++] = buf;
+       used += len;
+
+       len = snprintf(buf + used, buf_len - used, "%s/%s", FIT_CONFS_PATH,
+                      conf_name) + 1;
+       if (used + len > buf_len)
+               return -ENOSPC;
+       node_inc[count++] = buf + used;
+       used += len;
+
+       /* Process each image referenced by the config */
+       image_count = 0;
+       fdt_for_each_property_offset(prop_offset, fit, conf_noffset) {
+               const char *prop_name;
+               int img_count, i;
+
+               fdt_getprop_by_offset(fit, prop_offset, &prop_name, NULL);
+               if (!prop_name)
+                       continue;
+
+               /* Skip properties that are not image references */
+               if (!strcmp(prop_name, FIT_DESC_PROP) ||
+                   !strcmp(prop_name, FIT_COMPAT_PROP) ||
+                   !strcmp(prop_name, FIT_DEFAULT_PROP))
+                       continue;
+
+               img_count = fdt_stringlist_count(fit, conf_noffset, prop_name);
+               for (i = 0; i < img_count; i++) {
+                       int noffset;
+
+                       noffset = fit_conf_get_prop_node_index(fit,
+                                                              conf_noffset,
+                                                              prop_name, i);
+                       if (noffset < 0)
+                               continue;
+
+                       ret = fit_config_add_hash(fit, noffset, node_inc,
+                                                 &count, max_nodes, buf, &used,
+                                                 buf_len);
+                       if (ret < 0)
+                               return ret;
+
+                       image_count++;
+               }
+       }
+
+       if (!image_count) {
+               printf("No images in config '%s'\n", conf_name);
+               return -ENOMSG;
+       }
+
+       return count;
+}
+
 /**
  * fit_config_check_sig() - Check the signature of a config
  *
@@ -259,19 +433,16 @@ static int fit_config_check_sig(const void *fit, int noffset,
                                char **err_msgp)
 {
        char * const exc_prop[] = {"data", "data-size", "data-position"};
-       const char *prop, *end, *name;
+       char *node_inc[IMAGE_MAX_HASHED_NODES];
+       char hash_buf[FIT_MAX_HASH_PATH_BUF];
        struct image_sign_info info;
        const uint32_t *strings;
-       const char *config_name;
        uint8_t *fit_value;
        int fit_value_len;
-       bool found_config;
        int max_regions;
-       int i, prop_len;
        char path[200];
        int count;
 
-       config_name = fit_get_name(fit, conf_noffset, NULL);
        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));
@@ -286,45 +457,12 @@ static int fit_config_check_sig(const void *fit, int noffset,
                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;
-       }
-
-       if (prop && prop_len > 0 && prop[prop_len - 1] != '\0') {
-               *err_msgp = "hashed-nodes property must be null-terminated";
-               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);
-       found_config = false;
-       for (name = prop, i = 0; name < end; name += strlen(name) + 1, i++) {
-               debug("   '%s'\n", name);
-               node_inc[i] = (char *)name;
-               if (!strncmp(FIT_CONFS_PATH, name, strlen(FIT_CONFS_PATH)) &&
-                   name[sizeof(FIT_CONFS_PATH) - 1] == '/' &&
-                   !strcmp(name + sizeof(FIT_CONFS_PATH), config_name)) {
-                       debug("      (found config node %s)", config_name);
-                       found_config = true;
-               }
-       }
-       if (!found_config) {
-               *err_msgp = "Selected config not in hashed nodes";
+       /* Build the node list from the config, ignoring hashed-nodes */
+       count = fit_config_get_hash_list(fit, conf_noffset,
+                                        node_inc, IMAGE_MAX_HASHED_NODES,
+                                        hash_buf, sizeof(hash_buf));
+       if (count < 0) {
+               *err_msgp = "Failed to build hash node list";
                return -1;
        }