[meta-ti][master][PATCH v2 1/3] dm-verity-upstream: Add dynamic layer for meta-security dm-verity

[Atharv Dubey <a-dubey@ti.com>]

Add an optional dynamic layer enabling dm-verity block-level integrity
verification of the root filesystem for TI K3 platforms, using
meta-security's stock dm-verity mechanism as-is.

dm-verity hashes the rootfs at build time; at boot, a dedicated
initramfs loads the root hash and the kernel checks every block read
against it. Wires DM_VERITY_IMAGE/WKS_FILE for the K3 boot chain,
hooking do_image_wic instead of INITRAMFS_IMAGE to avoid a 3-way
circular dependency through kernel-fit-image.bbclass.

DM_VERITY_IMAGE selects which image recipe gets verity-enabled
(default arago-base-image, overridable in local.conf); all effects are
scoped to PN == DM_VERITY_IMAGE, so building any other image type is
unaffected. Only active when the "security" layer and dm-verity-upstream
feature are enabled.

Signed-off-by: Atharv Dubey <a-dubey@ti.com>

---
v2:
 - Replaced hardcoded /dev/mmcblk1p2 with UUID
 - Added install -d before installing the udev ignorelist file
 - Changed the FILES automount to specify the exact file
---
 meta-ti-bsp/conf/layer.conf                     |  3 +++
 meta-ti-bsp/conf/machine/include/k3.inc         | 10 ++++++++++
 .../conf/include/dm-verity-upstream.inc         | 17 +++++++++++++++++
 .../udev/files/dm-verity.ignorelist             |  1 +
 .../recipes-core/udev/udev-extraconf_%.bbappend | 15 +++++++++++++++
 meta-ti-bsp/files/wic/k3-verity.wks.in          |  5 +++++
 6 files changed, 51 insertions(+)
 create mode 100644 meta-ti-bsp/dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc
 create mode 100644 meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/files/dm-verity.ignorelist
 create mode 100644 meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/udev-extraconf_%.bbappend
 create mode 100644 meta-ti-bsp/files/wic/k3-verity.wks.in

diff --git a/meta-ti-bsp/conf/layer.conf b/meta-ti-bsp/conf/layer.conf
index 3cc54aa4..aca35cd3 100644
--- a/meta-ti-bsp/conf/layer.conf
+++ b/meta-ti-bsp/conf/layer.conf
@@ -20,12 +20,15 @@ LAYERDEPENDS_meta-ti-bsp = " \
 LAYERRECOMMENDS_meta-ti-bsp = " \
     openembedded-layer \
     tpm-layer \
+    security \
 "
 
 BBFILES_DYNAMIC += " \
     openembedded-layer:${LAYERDIR}/dynamic-layers/openembedded-layer/recipes*/*/*.bbappend \
     tpm-layer:${LAYERDIR}/dynamic-layers/tpm-layer/recipes*/*/*.bb \
     tpm-layer:${LAYERDIR}/dynamic-layers/tpm-layer/recipes*/*/*.bbappend \
+    security:${LAYERDIR}/dynamic-layers/security-layer/recipes*/*/*.bb \
+    security:${LAYERDIR}/dynamic-layers/security-layer/recipes*/*/*.bbappend \
 "
 
 SIGGEN_EXCLUDERECIPES_ABISAFE += " \
diff --git a/meta-ti-bsp/conf/machine/include/k3.inc b/meta-ti-bsp/conf/machine/include/k3.inc
index 2ebbfb9e..e23e0ead 100644
--- a/meta-ti-bsp/conf/machine/include/k3.inc
+++ b/meta-ti-bsp/conf/machine/include/k3.inc
@@ -64,3 +64,13 @@ FALCON_INCLUDE = ""
 FALCON_INCLUDE:ti-falcon = "conf/machine/include/ti-falcon.inc"
 
 require ${FALCON_INCLUDE}
+
+# Upstream dm-verity path: meta-security's own dm-verity-img.bbclass +
+# dm-verity-image-initramfs, used as-is (build-time hashing). Only active
+# when the security layer is present and this feature is explicitly
+# requested -- see dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc
+DISTRO_FEATURES[validitems] += "dm-verity-upstream"
+
+DM_VERITY_UPSTREAM_INCLUDE = "${@bb.utils.contains('DISTRO_FEATURES', 'dm-verity-upstream', 'dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc', '', d)}"
+
+require ${DM_VERITY_UPSTREAM_INCLUDE}
diff --git a/meta-ti-bsp/dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc b/meta-ti-bsp/dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc
new file mode 100644
index 00000000..4de9e2fb
--- /dev/null
+++ b/meta-ti-bsp/dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc
@@ -0,0 +1,17 @@
+# Enables dm-verity to check the rootfs for tampering on TI K3 boards.
+DM_VERITY_IMAGE ?= "arago-base-image"
+DM_VERITY_IMAGE_TYPE = "ext4"
+IMAGE_CLASSES += "dm-verity-img"
+
+DM_VERITY_INITRAMFS_IMAGE = "dm-verity-image-initramfs"
+
+python () {
+    if d.getVar('PN') != d.getVar('DM_VERITY_IMAGE'):
+        return
+
+    d.setVar('WKS_FILE', 'k3-verity.wks.in')
+    d.appendVar('EXTRA_IMAGE_FEATURES', ' read-only-rootfs')
+    d.appendVar('WICVARS', ' DM_VERITY_IMAGE DM_VERITY_IMAGE_TYPE IMAGE_NAME_SUFFIX IMGDEPLOYDIR')
+    d.appendVarFlag('do_image_wic', 'depends', ' %s:do_image_complete' % d.getVar('DM_VERITY_INITRAMFS_IMAGE'))
+    d.appendVar('IMAGE_BOOT_FILES', ' %s-%s.cpio.gz' % (d.getVar('DM_VERITY_INITRAMFS_IMAGE'), d.getVar('MACHINE')))
+}
diff --git a/meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/files/dm-verity.ignorelist b/meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/files/dm-verity.ignorelist
new file mode 100644
index 00000000..5af878c9
--- /dev/null
+++ b/meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/files/dm-verity.ignorelist
@@ -0,0 +1 @@
+/dev/mmcblk1p2
diff --git a/meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/udev-extraconf_%.bbappend b/meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/udev-extraconf_%.bbappend
new file mode 100644
index 00000000..dc6b37f9
--- /dev/null
+++ b/meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/udev-extraconf_%.bbappend
@@ -0,0 +1,15 @@
+# Under dm-verity, the raw root partition looks unmounted to udev's
+# auto-mount check, so it tries to mount it a second time on its own,
+# outside of dm-verity's protection. This tells it to skip that partition.
+FILESEXTRAPATHS:prepend := "${THISDIR}/files:"
+
+SRC_URI += "${@bb.utils.contains('DISTRO_FEATURES', 'dm-verity-upstream', 'file://dm-verity.ignorelist', '', d)}"
+
+do_install:append() {
+    if ${@bb.utils.contains('DISTRO_FEATURES', 'dm-verity-upstream', 'true', 'false', d)}; then
+        install -d ${D}${sysconfdir}/udev/mount.ignorelist.d
+        install -m 0644 ${UNPACKDIR}/dm-verity.ignorelist ${D}${sysconfdir}/udev/mount.ignorelist.d/dm-verity
+    fi
+}
+
+FILES:${PN}-automount += "${sysconfdir}/udev/mount.ignorelist.d/dm-verity"
diff --git a/meta-ti-bsp/files/wic/k3-verity.wks.in b/meta-ti-bsp/files/wic/k3-verity.wks.in
new file mode 100644
index 00000000..2ad0609f
--- /dev/null
+++ b/meta-ti-bsp/files/wic/k3-verity.wks.in
@@ -0,0 +1,5 @@
+# Disk layout for a board that boots with dm-verity enabled.
+
+bootloader --timeout=3 --append="rootfstype=ext4 root=PARTUUID=${UUID_2} ${TI_WKS_BOOTLOADER_APPEND}"
+part --source bootimg-efi --sourceparams="loader=${EFI_PROVIDER},initrd=${DM_VERITY_INITRAMFS_IMAGE}-${MACHINE}.cpio.gz" --fstype=vfat --label boot --active --align 1024 --use-uuid --fixed-size 128M
+part / --source rawcopy --sourceparams="file=${IMGDEPLOYDIR}/${DM_VERITY_IMAGE}-${MACHINE}${IMAGE_NAME_SUFFIX}.${DM_VERITY_IMAGE_TYPE}.verity" --align 1024 --use-uuid
-- 
2.34.1