Merge patch series "fit: dm-verity support"

Daniel Golle <[email protected]> says:

This series adds dm-verity support to U-Boot's FIT image infrastructure.
It is the first logical subset of the larger OpenWrt boot method series
posted as an RFC in February 2026 [1], extracted here for independent
review and merging.

OpenWrt's firmware model embeds a read-only squashfs or erofs root
filesystem directly inside a uImage.FIT container as a FILESYSTEM-type
loadable FIT image. At boot the kernel maps this sub-image directly from
the underlying block device via the fitblk driver (/dev/fit0, /dev/fit1,
...), the goal is that the bootloader never even copies it to RAM.

dm-verity enables the kernel to verify the integrity of those mapped
filesystems at read time, with a Merkle hash tree stored contiguously in
the same sub-image just after the data. Two kernel command-line
parameters are required:

  dm-mod.create=   -- the device-mapper target table for the verity device
  dm-mod.waitfor=  -- a comma-separated list of block devices to wait for
                      before dm-init sets up the targets (needed when fitblk
                      probes late, e.g. because it depends on NVMEM
                      calibration data)

The FIT dm-verity node schema was upstreamed into the flat-image-tree
specification [2], which this implementation tries to follow exactly.

The runtime feature is guarded behind CONFIG_FIT_VERITY. If not
enabled the resulting binary size remains unchanged. If enabled the
binary size increases by about 3kB.

[1] previous submissions:
    RFC: https://www.mail-archive.com/[email protected]/msg565945.html
    v1:  https://www.mail-archive.com/[email protected]/msg569472.html
    v2:  https://www.mail-archive.com/[email protected]/msg570599.html
    v3:  https://www.mail-archive.com/[email protected]/msg573223.html
    v4:  https://www.mail-archive.com/[email protected]/msg574000.html

[2] flat-image-tree dm-verity node spec:
    https://github.com/open-source-firmware/flat-image-tree/commit/795fd5fd7f0121d0cb03efb1900aafc61c704771

Link: https://lore.kernel.org/r/[email protected]

4 files changed, 484 insertions, 0 deletions

diff --git a/test/boot/Makefile b/test/boot/Makefile
index 89538d4f0a6..d98f212b243 100644
--- a/test/boot/Makefile
+++ b/test/boot/Makefile
@@ -15,6 +15,7 @@ endif
 ifdef CONFIG_SANDBOX
 obj-$(CONFIG_$(PHASE_)CMDLINE) += bootm.o
 endif
+obj-$(CONFIG_$(PHASE_)FIT_VERITY) += fit_verity.o
 obj-$(CONFIG_MEASURED_BOOT) += measurement.o
 
 ifdef CONFIG_OF_LIVE
diff --git a/test/boot/fit_verity.c b/test/boot/fit_verity.c
new file mode 100644
index 00000000000..7459a9d6f81
--- /dev/null
+++ b/test/boot/fit_verity.c
@@ -0,0 +1,306 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Tests for FIT dm-verity cmdline generation
+ *
+ * Copyright 2026 Daniel Golle <[email protected]>
+ */
+
+#include <image.h>
+#include <test/test.h>
+#include <test/ut.h>
+
+#define FIT_VERITY_TEST(_name, _flags)	UNIT_TEST(_name, _flags, fit_verity)
+
+/* FIT blob buffer size — generous to avoid FDT_ERR_NOSPACE */
+#define FIT_BUF_SIZE	4096
+
+/* Test digest (32 bytes = sha256) */
+static const u8 test_digest[32] = {
+	0x8e, 0x67, 0x91, 0x63, 0x7f, 0x93, 0xcb, 0xb8,
+	0x1f, 0xc4, 0x52, 0x99, 0xe2, 0x03, 0xcb, 0xe8,
+	0x5c, 0xa2, 0xe4, 0x7a, 0x38, 0xf5, 0x05, 0x1b,
+	0xdd, 0xee, 0xce, 0x92, 0xd7, 0xb1, 0xc9, 0xf9,
+};
+
+/* Test salt (32 bytes) */
+static const u8 test_salt[32] = {
+	0xaa, 0x7b, 0x11, 0xf8, 0xdb, 0x8f, 0xe2, 0xe5,
+	0xbf, 0xd4, 0xec, 0xa1, 0xd1, 0x8a, 0x22, 0xb5,
+	0xde, 0x7e, 0xa3, 0x9d, 0x2e, 0x1b, 0x93, 0xbb,
+	0x72, 0x72, 0xce, 0x0c, 0x6c, 0xa3, 0xcc, 0x8e,
+};
+
+/**
+ * build_verity_fit() - construct a minimal FIT blob with dm-verity metadata
+ * @buf:		output buffer (at least FIT_BUF_SIZE bytes)
+ * @num_loadables:	number of filesystem loadables to create (1 or 2)
+ *
+ * Builds a FIT blob containing:
+ *  - /images/rootfsN  with type="filesystem" and a dm-verity subnode
+ *  - /configurations/conf-1  referencing the loadable(s)
+ *
+ * Return: configuration node offset, or -ve on error
+ */
+static int build_verity_fit(void *buf, int num_loadables)
+{
+	int images_node, conf_node, confs_node, img_node, verity_node;
+	fdt32_t val;
+	int ret, i;
+	char name[32];
+	/*
+	 * Build the loadables string list. FDT stringlists are concatenated
+	 * NUL-terminated strings. E.g. "rootfs0\0rootfs1\0"
+	 */
+	char loadables[128];
+	int loadables_len = 0;
+
+	ret = fdt_create_empty_tree(buf, FIT_BUF_SIZE);
+	if (ret)
+		return ret;
+
+	/* /images */
+	images_node = fdt_add_subnode(buf, 0, "images");
+	if (images_node < 0)
+		return images_node;
+
+	for (i = 0; i < num_loadables; i++) {
+		snprintf(name, sizeof(name), "rootfs%d", i);
+
+		img_node = fdt_add_subnode(buf, images_node, name);
+		if (img_node < 0)
+			return img_node;
+
+		ret = fdt_setprop_string(buf, img_node, FIT_TYPE_PROP,
+					 "filesystem");
+		if (ret)
+			return ret;
+
+		verity_node = fdt_add_subnode(buf, img_node,
+					      FIT_VERITY_NODENAME);
+		if (verity_node < 0)
+			return verity_node;
+
+		ret = fdt_setprop_string(buf, verity_node,
+					 FIT_VERITY_ALGO_PROP, "sha256");
+		if (ret)
+			return ret;
+
+		val = cpu_to_fdt32(4096);
+		ret = fdt_setprop(buf, verity_node, FIT_VERITY_DBS_PROP,
+				  &val, sizeof(val));
+		if (ret)
+			return ret;
+
+		ret = fdt_setprop(buf, verity_node, FIT_VERITY_HBS_PROP,
+				  &val, sizeof(val));
+		if (ret)
+			return ret;
+
+		val = cpu_to_fdt32(100);
+		ret = fdt_setprop(buf, verity_node, FIT_VERITY_NBLK_PROP,
+				  &val, sizeof(val));
+		if (ret)
+			return ret;
+
+		val = cpu_to_fdt32(100);
+		ret = fdt_setprop(buf, verity_node, FIT_VERITY_HBLK_PROP,
+				  &val, sizeof(val));
+		if (ret)
+			return ret;
+
+		ret = fdt_setprop(buf, verity_node, FIT_VERITY_DIGEST_PROP,
+				  test_digest, sizeof(test_digest));
+		if (ret)
+			return ret;
+
+		ret = fdt_setprop(buf, verity_node, FIT_VERITY_SALT_PROP,
+				  test_salt, sizeof(test_salt));
+		if (ret)
+			return ret;
+
+		/* Append to loadables stringlist */
+		loadables_len += snprintf(loadables + loadables_len,
+					  sizeof(loadables) - loadables_len,
+					  "%s", name) + 1;
+	}
+
+	/* /configurations/conf-1 */
+	confs_node = fdt_add_subnode(buf, 0, "configurations");
+	if (confs_node < 0)
+		return confs_node;
+
+	conf_node = fdt_add_subnode(buf, confs_node, "conf-1");
+	if (conf_node < 0)
+		return conf_node;
+
+	ret = fdt_setprop(buf, conf_node, FIT_LOADABLE_PROP,
+			  loadables, loadables_len);
+	if (ret)
+		return ret;
+
+	return conf_node;
+}
+
+/* Test: single dm-verity loadable produces correct cmdline fragments */
+static int fit_verity_test_single(struct unit_test_state *uts)
+{
+	char buf[FIT_BUF_SIZE];
+	struct bootm_headers images;
+	int conf_noffset;
+
+	conf_noffset = build_verity_fit(buf, 1);
+	ut_assert(conf_noffset >= 0);
+
+	memset(&images, 0, sizeof(images));
+	ut_assertok(fit_verity_build_cmdline(buf, conf_noffset, &images));
+
+	/* dm_mod_create should contain the target spec for rootfs0 */
+	ut_assertnonnull(images.dm_mod_create);
+	ut_assert(strstr(images.dm_mod_create, "rootfs0,,,"));
+	ut_assert(strstr(images.dm_mod_create, "verity 1"));
+	ut_assert(strstr(images.dm_mod_create, "/dev/fit0"));
+	ut_assert(strstr(images.dm_mod_create, "4096 4096 100 100"));
+	ut_assert(strstr(images.dm_mod_create, "sha256"));
+	/* Check hex-encoded digest prefix */
+	ut_assert(strstr(images.dm_mod_create, "8e6791637f93cbb8"));
+	/* Check hex-encoded salt prefix */
+	ut_assert(strstr(images.dm_mod_create, "aa7b11f8db8fe2e5"));
+
+	/* dm_mod_waitfor should reference /dev/fit0 */
+	ut_assertnonnull(images.dm_mod_waitfor);
+	ut_asserteq_str("/dev/fit0", images.dm_mod_waitfor);
+
+	fit_verity_free(&images);
+	ut_assertnull(images.dm_mod_create);
+	ut_assertnull(images.dm_mod_waitfor);
+
+	return 0;
+}
+FIT_VERITY_TEST(fit_verity_test_single, 0);
+
+/* Test: FIT with no dm-verity subnode returns 0, pointers stay NULL */
+static int fit_verity_test_no_verity(struct unit_test_state *uts)
+{
+	char buf[FIT_BUF_SIZE];
+	struct bootm_headers images;
+	int conf_node, images_node, img_node, confs_node;
+	int ret;
+
+	ret = fdt_create_empty_tree(buf, FIT_BUF_SIZE);
+	ut_assertok(ret);
+
+	images_node = fdt_add_subnode(buf, 0, "images");
+	ut_assert(images_node >= 0);
+
+	img_node = fdt_add_subnode(buf, images_node, "rootfs");
+	ut_assert(img_node >= 0);
+	ut_assertok(fdt_setprop_string(buf, img_node, FIT_TYPE_PROP,
+				       "filesystem"));
+	/* No dm-verity subnode */
+
+	confs_node = fdt_add_subnode(buf, 0, "configurations");
+	ut_assert(confs_node >= 0);
+	conf_node = fdt_add_subnode(buf, confs_node, "conf-1");
+	ut_assert(conf_node >= 0);
+	ut_assertok(fdt_setprop_string(buf, conf_node, FIT_LOADABLE_PROP,
+				       "rootfs"));
+
+	memset(&images, 0, sizeof(images));
+	ut_asserteq(0, fit_verity_build_cmdline(buf, conf_node, &images));
+	ut_assertnull(images.dm_mod_create);
+	ut_assertnull(images.dm_mod_waitfor);
+
+	return 0;
+}
+FIT_VERITY_TEST(fit_verity_test_no_verity, 0);
+
+/* Test: two dm-verity loadables produce combined cmdline */
+static int fit_verity_test_two_loadables(struct unit_test_state *uts)
+{
+	char buf[FIT_BUF_SIZE];
+	struct bootm_headers images;
+	int conf_noffset;
+
+	conf_noffset = build_verity_fit(buf, 2);
+	ut_assert(conf_noffset >= 0);
+
+	memset(&images, 0, sizeof(images));
+	ut_assertok(fit_verity_build_cmdline(buf, conf_noffset, &images));
+
+	/* Both targets should appear, separated by ";" */
+	ut_assertnonnull(images.dm_mod_create);
+	ut_assert(strstr(images.dm_mod_create, "rootfs0,,,"));
+	ut_assert(strstr(images.dm_mod_create, ";rootfs1,,,"));
+	ut_assert(strstr(images.dm_mod_create, "/dev/fit0"));
+	ut_assert(strstr(images.dm_mod_create, "/dev/fit1"));
+
+	/* dm_mod_waitfor should list both devices */
+	ut_assertnonnull(images.dm_mod_waitfor);
+	ut_assert(strstr(images.dm_mod_waitfor, "/dev/fit0"));
+	ut_assert(strstr(images.dm_mod_waitfor, "/dev/fit1"));
+
+	fit_verity_free(&images);
+	return 0;
+}
+FIT_VERITY_TEST(fit_verity_test_two_loadables, 0);
+
+/* Test: invalid block size (not power of two) returns -EINVAL */
+static int fit_verity_test_bad_blocksize(struct unit_test_state *uts)
+{
+	char buf[FIT_BUF_SIZE];
+	struct bootm_headers images;
+	int images_node, conf_node, confs_node, img_node, verity_node;
+	fdt32_t val;
+	int ret;
+
+	ret = fdt_create_empty_tree(buf, FIT_BUF_SIZE);
+	ut_assertok(ret);
+
+	images_node = fdt_add_subnode(buf, 0, "images");
+	ut_assert(images_node >= 0);
+
+	img_node = fdt_add_subnode(buf, images_node, "rootfs");
+	ut_assert(img_node >= 0);
+	ut_assertok(fdt_setprop_string(buf, img_node, FIT_TYPE_PROP,
+				       "filesystem"));
+
+	verity_node = fdt_add_subnode(buf, img_node, FIT_VERITY_NODENAME);
+	ut_assert(verity_node >= 0);
+
+	ut_assertok(fdt_setprop_string(buf, verity_node,
+				       FIT_VERITY_ALGO_PROP, "sha256"));
+
+	/* 3000 is not a power of two */
+	val = cpu_to_fdt32(3000);
+	ut_assertok(fdt_setprop(buf, verity_node, FIT_VERITY_DBS_PROP,
+				&val, sizeof(val)));
+	val = cpu_to_fdt32(4096);
+	ut_assertok(fdt_setprop(buf, verity_node, FIT_VERITY_HBS_PROP,
+				&val, sizeof(val)));
+
+	val = cpu_to_fdt32(100);
+	ut_assertok(fdt_setprop(buf, verity_node, FIT_VERITY_NBLK_PROP,
+				&val, sizeof(val)));
+	ut_assertok(fdt_setprop(buf, verity_node, FIT_VERITY_HBLK_PROP,
+				&val, sizeof(val)));
+
+	ut_assertok(fdt_setprop(buf, verity_node, FIT_VERITY_DIGEST_PROP,
+				test_digest, sizeof(test_digest)));
+	ut_assertok(fdt_setprop(buf, verity_node, FIT_VERITY_SALT_PROP,
+				test_salt, sizeof(test_salt)));
+
+	confs_node = fdt_add_subnode(buf, 0, "configurations");
+	ut_assert(confs_node >= 0);
+	conf_node = fdt_add_subnode(buf, confs_node, "conf-1");
+	ut_assert(conf_node >= 0);
+	ut_assertok(fdt_setprop_string(buf, conf_node, FIT_LOADABLE_PROP,
+				       "rootfs"));
+
+	memset(&images, 0, sizeof(images));
+	ut_asserteq(-EINVAL, fit_verity_build_cmdline(buf, conf_node, &images));
+	ut_assertnull(images.dm_mod_create);
+	ut_assertnull(images.dm_mod_waitfor);
+
+	return 0;
+}
+FIT_VERITY_TEST(fit_verity_test_bad_blocksize, 0);
diff --git a/test/cmd_ut.c b/test/cmd_ut.c
index 44e5fdfdaa6..d1b376f617c 100644
--- a/test/cmd_ut.c
+++ b/test/cmd_ut.c
@@ -59,6 +59,7 @@ SUITE_DECL(env);
 SUITE_DECL(exit);
 SUITE_DECL(fdt);
 SUITE_DECL(fdt_overlay);
+SUITE_DECL(fit_verity);
 SUITE_DECL(font);
 SUITE_DECL(hush);
 SUITE_DECL(lib);
@@ -86,6 +87,7 @@ static struct suite suites[] = {
 	SUITE(exit, "shell exit and variables"),
 	SUITE(fdt, "fdt command"),
 	SUITE(fdt_overlay, "device tree overlays"),
+	SUITE(fit_verity, "FIT dm-verity cmdline generation"),
 	SUITE(font, "font command"),
 	SUITE(hush, "hush behaviour"),
 	SUITE(lib, "library functions"),
diff --git a/test/py/tests/test_fit_verity.py b/test/py/tests/test_fit_verity.py
new file mode 100644
index 00000000000..f1b6262ed0e
--- /dev/null
+++ b/test/py/tests/test_fit_verity.py
@@ -0,0 +1,175 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Copyright 2026 Daniel Golle <[email protected]>
+
+"""
+Test mkimage dm-verity Merkle-tree generation
+
+Build a minimal .its with a dm-verity subnode (user-provided properties only),
+run mkimage -E, and verify that the computed properties (digest, salt,
+num-data-blocks, hash-start-block) are written into the resulting FIT.
+The computed digest is then re-verified by running ``veritysetup verify``
+against the external data section of the .itb.
+
+This test does not run the sandbox. It only exercises the host tool 'mkimage'.
+Requires 'veritysetup' from the cryptsetup package on the build host.
+"""
+
+import os
+import struct
+import pytest
+import utils
+
+ITS_TEMPLATE = """\
+/dts-v1/;
+
+/ {
+    description = "dm-verity test";
+    #address-cells = <1>;
+
+    images {
+        rootfs {
+            description = "test filesystem";
+            data = /incbin/("./rootfs.bin");
+            type = "filesystem";
+            arch = "sandbox";
+            compression = "none";
+
+            dm-verity {
+                algo = "sha256";
+                data-block-size = <%d>;
+                hash-block-size = <%d>;
+            };
+        };
+    };
+
+    configurations {
+        default = "conf-1";
+        conf-1 {
+            description = "test config";
+            loadables = "rootfs";
+        };
+    };
+};
+"""
+
+def _fdt_totalsize(path):
+    """Read the totalsize field from an FDT header (offset 4, big-endian u32)."""
+    with open(path, 'rb') as f:
+        magic, totalsize = struct.unpack('>II', f.read(8))
+    assert magic == 0xd00dfeed, f'not an FDT: magic={magic:#x}'
+    return totalsize
+
+
+def _run_round_trip(ubman, tempdir, data_block_size, hash_block_size):
+    """Build a FIT with dm-verity, verify written properties, re-verify with veritysetup."""
+    mkimage = ubman.config.build_dir + '/tools/mkimage'
+
+    rootfs_file = os.path.join(tempdir, 'rootfs.bin')
+    its_file = os.path.join(tempdir, 'image.its')
+    fit_file = os.path.join(tempdir, 'image.itb')
+
+    # 64 data blocks of 0xa5
+    num_blocks = 64
+    data_size = data_block_size * num_blocks
+    with open(rootfs_file, 'wb') as f:
+        f.write(bytes([0xa5]) * data_size)
+
+    with open(its_file, 'w') as f:
+        f.write(ITS_TEMPLATE % (data_block_size, hash_block_size))
+
+    dtc_args = f'-I dts -O dtb -i {tempdir}'
+    utils.run_and_log(ubman,
+                      [mkimage, '-E', '-D', dtc_args, '-f', its_file, fit_file])
+
+    def fdt_get(node, prop):
+        val = utils.run_and_log(ubman, f'fdtget {fit_file} {node} {prop}')
+        return val.strip()
+
+    def fdt_get_hex(node, prop):
+        val = utils.run_and_log(ubman, f'fdtget -tbx {fit_file} {node} {prop}')
+        return ''.join(b.zfill(2) for b in val.strip().split())
+
+    verity_path = '/images/rootfs/dm-verity'
+
+    assert fdt_get(verity_path, 'algo') == 'sha256'
+    assert int(fdt_get(verity_path, 'data-block-size')) == data_block_size
+    assert int(fdt_get(verity_path, 'hash-block-size')) == hash_block_size
+
+    nblk = int(fdt_get(verity_path, 'num-data-blocks'))
+    assert nblk == num_blocks, f'num-data-blocks {nblk} != {num_blocks}'
+
+    hblk = int(fdt_get(verity_path, 'hash-start-block'))
+    # With --no-superblock, hash-start-block = data_size / hash-block-size
+    assert hblk == data_size // hash_block_size, \
+        f'hash-start-block {hblk} != {data_size // hash_block_size}'
+
+    digest = fdt_get_hex(verity_path, 'digest')
+    assert len(digest) == 64 and digest != '0' * 64
+    salt = fdt_get_hex(verity_path, 'salt')
+    assert len(salt) == 64
+
+    # Re-verify the digest with veritysetup against the .itb's external data.
+    # With -E, image data sits after the FIT FDT at (fdt_totalsize + data-offset).
+    data_offset = int(fdt_get('/images/rootfs', 'data-offset'))
+    data_size_full = int(fdt_get('/images/rootfs', 'data-size'))
+    ext_pos = _fdt_totalsize(fit_file) + data_offset
+    expanded = os.path.join(tempdir, 'expanded.bin')
+    with open(fit_file, 'rb') as src, open(expanded, 'wb') as dst:
+        src.seek(ext_pos)
+        dst.write(src.read(data_size_full))
+
+    utils.run_and_log(ubman, [
+        'veritysetup', 'verify', expanded, expanded, digest,
+        '--no-superblock',
+        f'--data-block-size={data_block_size}',
+        f'--hash-block-size={hash_block_size}',
+        f'--data-blocks={nblk}',
+        '--hash=sha256',
+        f'--salt={salt}',
+        f'--hash-offset={data_size}',
+    ])
+
+
[email protected]('dtc')
[email protected]('fdtget')
[email protected]('veritysetup')
[email protected]('data_block_size,hash_block_size,subdir', [
+    (4096, 4096, 'verity-equal'),
+    (4096, 1024, 'verity-unequal'),
+])
+def test_mkimage_verity(ubman, data_block_size, hash_block_size, subdir):
+    """mkimage writes correct dm-verity properties and the digest verifies.
+
+    Run with matching and mismatched block sizes so the
+    ``hash-start-block != num-data-blocks`` path is exercised.
+    """
+    tempdir = os.path.join(ubman.config.result_dir, subdir)
+    os.makedirs(tempdir, exist_ok=True)
+    _run_round_trip(ubman, tempdir, data_block_size, hash_block_size)
+
+
[email protected]('dtc')
[email protected]('veritysetup')
+def test_mkimage_verity_requires_external(ubman):
+    """mkimage rejects dm-verity without -E with the expected diagnostic."""
+
+    mkimage = ubman.config.build_dir + '/tools/mkimage'
+    tempdir = os.path.join(ubman.config.result_dir, 'verity_no_ext')
+    os.makedirs(tempdir, exist_ok=True)
+
+    rootfs_file = os.path.join(tempdir, 'rootfs.bin')
+    its_file = os.path.join(tempdir, 'image.its')
+    fit_file = os.path.join(tempdir, 'image.itb')
+
+    with open(rootfs_file, 'wb') as f:
+        f.write(bytes([0xa5]) * 4096 * 8)
+
+    with open(its_file, 'w') as f:
+        f.write(ITS_TEMPLATE % (4096, 4096))
+
+    dtc_args = f'-I dts -O dtb -i {tempdir}'
+    utils.run_and_log_expect_exception(
+        ubman,
+        [mkimage, '-D', dtc_args, '-f', its_file, fit_file],
+        1, 'dm-verity requires external data')