From fe9877c7d9dea740985edd11f7ff583e311568be Mon Sep 17 00:00:00 2001 From: Daniel Golle Date: Tue, 28 Jul 2026 23:09:53 +0100 Subject: test: fit: verify dm-verity roothash is covered by the config signature A dm-verity protected filesystem image is not hashed by U-Boot; its integrity is delegated to the kernel, which trusts the roothash taken from the FIT dm-verity subnode. For that chain of trust to hold, the roothash (and salt) must be part of the region covered by the configuration signature, otherwise an attacker can replace both the filesystem and the roothash while keeping the signature valid. Add two independent checks of this property: - test/py/tests/test_fit_verity_sign.py signs a configuration that references a filesystem image carrying a dm-verity subnode, then confirms that tampering the roothash or the salt is rejected by fit_check_sign. A control that tampers a byte known to be signed proves the check can fail. A matching page is added under doc/develop/pytest/ so the module documentation is rendered with the rest of the generated docs. - test/boot/fit_verity.c gains a runtime unit test that builds the exact node list the configuration signature is computed over, turns it into hashed regions and checks both that the roothash bytes fall inside a signed region and that tampering them changes the hash. It needs no private key, so it also runs on real devices and uses the same hash path a device would. To let the unit test build the signed-region node list, rename the config node-list helper to fit_config_get_signed_nodes(), make it non-static and declare it in image.h. Signed-off-by: Daniel Golle Reviewed-by: Simon Glass --- include/image.h | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) (limited to 'include') diff --git a/include/image.h b/include/image.h index 4149ebbcce9..6edcb1995bf 100644 --- a/include/image.h +++ b/include/image.h @@ -1897,6 +1897,29 @@ struct image_region *fit_region_make_list(const void *fit, struct fdt_region *fdt_regions, int count, struct image_region *region); +/** + * fit_config_get_signed_nodes() - Build the list of nodes covered by a config + * signature + * + * Collects the paths of the nodes that the configuration signature is + * computed over: the root node, the configuration node, and for each image + * referenced by the configuration its node, its hash subnodes and its cipher + * and dm-verity subnodes. The result is the same node list used when creating + * and verifying the signature, and is suitable for passing to + * fdt_find_regions(). + * + * @fit: FIT blob + * @conf_noffset: Configuration node offset + * @node_inc: Array to fill with pointers to packed path strings + * @max_nodes: Number of entries in @node_inc + * @buf: Buffer for the packed null-terminated path strings + * @buf_len: Size of @buf + * Return: number of entries written to @node_inc, or -ve on error + */ +int fit_config_get_signed_nodes(const void *fit, int conf_noffset, + char **node_inc, int max_nodes, + char *buf, int buf_len); + static inline int fit_image_check_target_arch(const void *fdt, int node) { #ifndef USE_HOSTCC -- cgit v1.3.1