pcrlock: recompute PCR policy on completed system update

Bind the io.systemd.SysUpdate.Notify.OnCompletedUpdate() method in the
pcrlock Varlink server and hook a socket into
/run/systemd/sysupdate/notify/ via systemd-sysupdate-notify-pcrlock.socket,
enabled by default via the preset. When sysupdate signals a completed
update, we unconditionally re-run make-policy, since the set of measured
components may have changed.

presets/90-systemd.preset

@@ -40,6 +40,7 @@ enable systemd-report-sign-tsm.socket
 enable systemd-report.socket
 enable systemd-resolved.service
 enable systemd-sysext.service
+enable systemd-sysupdate-notify-pcrlock.socket
 enable systemd-timesyncd.service
 enable systemd-tpm2-clear.service
 enable systemd-userdbd.socket

src/pcrlock/pcrlock.c

@@ -61,6 +61,7 @@
 #include "unit-name.h"
 #include "utf8.h"
 #include "varlink-io.systemd.PCRLock.h"
+#include "varlink-io.systemd.SysUpdate.Notify.h"
 #include "varlink-util.h"
 #include "verbs.h"
 
@@ -5467,6 +5468,27 @@ static int vl_method_remove_policy(sd_varlink *link, sd_json_variant *parameters
         return sd_varlink_reply(link, NULL);
 }
 
+static int vl_method_on_completed_update(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        int r;
+
+        assert(link);
+
+        /* Triggered by systemd-sysupdate after an update completed. We deliberately ignore all parameters
+         * (we don't even dispatch them) and simply recompute the PCR policy unconditionally, since the set
+         * of measured components might have changed. */
+
+        /* Only honour update notifications if they come from root */
+        r = varlink_check_privileged_peer(link);
+        if (r < 0)
+                return r;
+
+        r = make_policy(/* force= */ false, /* recovery_pin_mode= */ RECOVERY_PIN_HIDE);
+        if (r < 0)
+                return r;
+
+        return sd_varlink_reply(link, NULL);
+}
+
 static int run(int argc, char *argv[]) {
         int r;
 
@@ -5496,15 +5518,19 @@ static int run(int argc, char *argv[]) {
                 if (r < 0)
                         return log_error_errno(r, "Failed to allocate Varlink server: %m");
 
-                r = sd_varlink_server_add_interface(varlink_server, &vl_interface_io_systemd_PCRLock);
+                r = sd_varlink_server_add_interface_many(
+                                varlink_server,
+                                &vl_interface_io_systemd_PCRLock,
+                                &vl_interface_io_systemd_SysUpdate_Notify);
                 if (r < 0)
-                        return log_error_errno(r, "Failed to add Varlink interface: %m");
+                        return log_error_errno(r, "Failed to add Varlink interfaces: %m");
 
                 r = sd_varlink_server_bind_method_many(
                                 varlink_server,
-                                "io.systemd.PCRLock.ReadEventLog", vl_method_read_event_log,
-                                "io.systemd.PCRLock.MakePolicy",   vl_method_make_policy,
-                                "io.systemd.PCRLock.RemovePolicy", vl_method_remove_policy);
+                                "io.systemd.PCRLock.ReadEventLog",                  vl_method_read_event_log,
+                                "io.systemd.PCRLock.MakePolicy",                    vl_method_make_policy,
+                                "io.systemd.PCRLock.RemovePolicy",                  vl_method_remove_policy,
+                                "io.systemd.SysUpdate.Notify.OnCompletedUpdate",    vl_method_on_completed_update);
                 if (r < 0)
                         return log_error_errno(r, "Failed to bind Varlink methods: %m");
 

units/meson.build

@@ -706,6 +706,14 @@ units = [
           'conditions' : ['ENABLE_BOOTLOADER', 'HAVE_OPENSSL', 'HAVE_TPM2'],
           'symlinks' : ['sockets.target.wants/'],
         },
+        {
+          'file' : 'systemd-sysupdate-notify-pcrlock@.service.in',
+          'conditions' : ['ENABLE_BOOTLOADER', 'HAVE_OPENSSL', 'HAVE_TPM2'],
+        },
+        {
+          'file' : 'systemd-sysupdate-notify-pcrlock.socket',
+          'conditions' : ['ENABLE_BOOTLOADER', 'HAVE_OPENSSL', 'HAVE_TPM2'],
+        },
         {
           'file' : 'systemd-portabled.service.in',
           'conditions' : ['ENABLE_PORTABLED'],

units/systemd-sysupdate-notify-pcrlock.socket

@@ -0,0 +1,29 @@
+#  SPDX-License-Identifier: LGPL-2.1-or-later
+#
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Recompute TPM PCR Policy on Completed System Update
+Documentation=man:systemd-pcrlock(8)
+DefaultDependencies=no
+After=tpm2.target
+Before=sockets.target
+ConditionSecurity=measured-uki
+
+[Socket]
+ListenStream=/run/systemd/sysupdate/notify/io.systemd.PCRLock
+FileDescriptorName=varlink
+SocketMode=0644
+Accept=yes
+MaxConnectionsPerSource=16
+XAttrEntryPoint=user.varlink=entrypoint
+XAttrListen=user.varlink=listen
+XAttrAccept=user.varlink=server
+
+[Install]
+WantedBy=sockets.target

units/systemd-sysupdate-notify-pcrlock@.service.in

@@ -0,0 +1,20 @@
+#  SPDX-License-Identifier: LGPL-2.1-or-later
+#
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Recompute TPM PCR Policy on Completed System Update
+Documentation=man:systemd-pcrlock(8)
+DefaultDependencies=no
+Conflicts=shutdown.target
+After=systemd-tpm2-setup.service
+After=systemd-remount-fs.service var.mount
+Before=shutdown.target
+
+[Service]
+ExecStart={{LIBEXECDIR}}/systemd-pcrlock --location=770