dm-verity-upstream: Add dynamic layer for meta-security dm-verity

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. Requires meta-security
to be present in bblayers.conf.

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. Set DM_VERITY_IMAGE to enable all the verity-related
recipes for that image; other images build as usual.

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

meta-ti-bsp/conf/layer.conf

@@ -22,6 +22,7 @@ LAYERRECOMMENDS_meta-ti-bsp = " \
     multimedia-layer \
     openembedded-layer \
     tpm-layer \
+    security \
 "
 
 BBFILES_DYNAMIC += " \
@@ -29,6 +30,8 @@ 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 += " \

meta-ti-bsp/conf/machine/include/k3.inc

@@ -61,3 +61,10 @@ FALCON_INCLUDE = ""
 FALCON_INCLUDE:ti-falcon = "conf/machine/include/ti-falcon.inc"
 
 require ${FALCON_INCLUDE}
+
+# dm-verity protects the rootfs listed in DM_VERITY_IMAGE; see dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc for what that turns on.
+DM_VERITY_IMAGE ??= ""
+
+DM_VERITY_UPSTREAM_INCLUDE = "${@'dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc' if d.getVar('DM_VERITY_IMAGE') else ''}"
+
+require ${DM_VERITY_UPSTREAM_INCLUDE}

meta-ti-bsp/dynamic-layers/security-layer/conf/include/dm-verity-upstream.inc

@@ -0,0 +1,21 @@
+# Enables dm-verity to check the rootfs for tampering on TI K3 boards.
+DM_VERITY_IMAGE_TYPE = "ext4"
+IMAGE_CLASSES += "dm-verity-img"
+
+# ti-core-initramfs.bbappend already wires the initramfs into the boot partition once dm-verity is enabled, so we don't need to do it here.
+
+python () {
+    import uuid
+
+    if d.getVar('PN') != d.getVar('DM_VERITY_IMAGE'):
+        return
+
+    # Derive the root partition's UUID from MACHINE so everyone computes the same one.
+    if not d.getVar('DM_VERITY_ROOT_PARTUUID'):
+        d.setVar('DM_VERITY_ROOT_PARTUUID',
+                 str(uuid.uuid5(uuid.NAMESPACE_DNS, 'dm-verity-root-%s' % d.getVar('MACHINE'))))
+
+    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 DM_VERITY_ROOT_PARTUUID')
+}

meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/udev-aragoconf_%.bbappend

@@ -0,0 +1,5 @@
+do_install:append() {
+    if ${@'true' if d.getVar('DM_VERITY_IMAGE') else 'false'}; then
+        : > ${D}${libdir}/udev/rules.d/50-arago.rules
+    fi
+}

meta-ti-bsp/dynamic-layers/security-layer/recipes-core/udev/udev-extraconf_%.bbappend

@@ -0,0 +1,6 @@
+# Nothing should ever get auto-mounted under dm-verity, so just kill the automounter.
+do_install:append() {
+    if ${@'true' if d.getVar('DM_VERITY_IMAGE') else 'false'}; then
+        : > ${D}${sysconfdir}/udev/rules.d/automount.rules
+    fi
+}

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=${DM_VERITY_ROOT_PARTUUID} ${TI_WKS_BOOTLOADER_APPEND}"
+part --source bootimg-efi --sourceparams="loader=${EFI_PROVIDER}${TI_WKS_INITRAMFS}" --fstype=vfat --label boot --active --align 1024 --use-uuid --fixed-size 128M
+part / --source rawcopy --sourceparams="file=${IMGDEPLOYDIR}/${DM_VERITY_IMAGE}-${MACHINE}${IMAGE_NAME_SUFFIX}.${DM_VERITY_IMAGE_TYPE}.verity" --align 1024 --uuid ${DM_VERITY_ROOT_PARTUUID}