report: add systemd-report-sign-tsm backend

A report signing backend that returns a confidential-computing
attestation report obtained via configfs-tsm. Implements
io.systemd.Report.Signer.Sign(): embeds the digest as the report's
inblob and returns the outblob (plus provider and any aux/manifest
blobs). Wired up as the "tsm" mechanism with a socket-activated service.

Signed-off-by: Paul Meyer <katexochen0@gmail.com>

units/meson.build

@@ -747,6 +747,8 @@ units = [
           'file' : 'systemd-report-sign-plain@.service.in',
           'conditions' : ['HAVE_OPENSSL'],
         },
+        { 'file' : 'systemd-report-sign-tsm.socket' },
+        { 'file' : 'systemd-report-sign-tsm@.service.in' },
         {
           'file' : 'systemd-resolved.service.in',
           'conditions' : ['ENABLE_RESOLVE'],

units/systemd-report-sign-tsm.socket

@@ -0,0 +1,27 @@
+# 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=Report Signing Socket (configfs-tsm)
+Documentation=man:systemd-report-sign-tsm@.service(8)
+DefaultDependencies=no
+Before=sockets.target shutdown.target
+Conflicts=shutdown.target
+ConditionSecurity=cvm
+
+[Socket]
+ListenStream=/run/systemd/report.sign/tsm
+FileDescriptorName=varlink
+SocketMode=0600
+Accept=yes
+MaxConnectionsPerSource=16
+RemoveOnStop=yes
+
+[Install]
+WantedBy=sockets.target

units/systemd-report-sign-tsm@.service.in

@@ -0,0 +1,46 @@
+# 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=Report Signing Service (configfs-tsm)
+Documentation=man:systemd-report-sign-tsm@.service(8)
+DefaultDependencies=no
+Before=shutdown.target
+Conflicts=shutdown.target
+Wants=sys-kernel-config.mount
+After=sys-kernel-config.mount
+
+[Service]
+ExecStart={{LIBEXECDIR}}/systemd-report-sign-tsm
+CapabilityBoundingSet=
+DeviceAllow=
+IPAddressDeny=any
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+NoNewPrivileges=yes
+PrivateDevices=yes
+PrivateIPC=yes
+PrivateNetwork=yes
+PrivateTmp=disconnected
+ProtectControlGroups=yes
+ProtectHome=yes
+ProtectHostname=yes
+ProtectKernelLogs=yes
+ProtectKernelModules=yes
+ProtectKernelTunables=yes
+ProtectSystem=strict
+ReadWritePaths=-/sys/kernel/config/tsm/report
+RestrictAddressFamilies=AF_UNIX
+RestrictNamespaces=yes
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
+RuntimeMaxSec=5min
+SystemCallArchitectures=native
+SystemCallErrorNumber=EPERM
+SystemCallFilter=@system-service