cryptsetup: measure via the pcrextend varlink service

Measure the volume key and unlock keyslot through io.systemd.PCRExtend instead of driving the TPM directly via tpm2-util, matching how the verity and imds measurements already work. Bank selection and the TPM context now live entirely in systemd-pcrextend. As a result the tpm2-measure-bank= crypttab option can no longer be honored per volume and is now a deprecated no-op. Signed-off-by: Paul Meyer <katexochen0@gmail.com>
2026-07-28 14:59:02 +02:00
parent 1812d8792f
commit 1bdf2db6f7
6 changed files with 138 additions and 101 deletions
@@ -0,0 +1,111 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: LGPL-2.1-or-later
+set -eux
+set -o pipefail
+
+# Tests that systemd-cryptsetup's tpm2-measure-pcr= option measures the volume key
+# through the io.systemd.PCRExtend Varlink service.
+#
+# Note: the tpm2-measure-keyslot-nvpcr= (NvPCR) path is intentionally not covered here. NvPCRs use a
+# signed PCR policy that must be anchored first (see TEST-70-TPM2.nvpcr.sh), which is heavy setup
+# orthogonal to what this test checks; the NvPCR extend-via-pcrextend path is already covered there.
+
+# shellcheck source=test/units/util.sh
+. "$(dirname "$0")"/util.sh
+
+export SYSTEMD_LOG_LEVEL=debug
+
+if ! command -v systemd-cryptsetup >/dev/null || ! tpm_has_pcr sha256 15; then
+    echo "systemd-cryptsetup or PCR 15 (sha256) not available, skipping cryptsetup measurement test"
+    exit 0
+fi
+
+IMAGE=""
+
+at_exit() {
+    if [[ $? -ne 0 ]]; then
+        # Dump the event log on failure, to ease debugging
+        jq --seq --slurp </run/log/systemd/tpm2-measure.log || :
+    fi
+
+    set +e
+
+    systemd-cryptsetup detach test-volume
+    rm -rf /run/systemd/system/systemd-pcrextend.socket.d
+    systemctl daemon-reload
+    systemctl restart systemd-pcrextend.socket
+    rm -f "${IMAGE:-}" /tmp/passphrase /tmp/vk /tmp/vk-hmac.bin \
+          /tmp/oldpcr15 /tmp/newpcr15 /tmp/measure-bank.log
+}
+
+trap at_exit EXIT
+
+# The socket carries ConditionSecurity=measured-os, which does not hold in the
+# test VM, so the Varlink service would never activate. Drop the condition so
+# systemd-cryptsetup can reach it, exactly like TEST-70-TPM2.pcrextend.sh does.
+mkdir -p /run/systemd/system/systemd-pcrextend.socket.d
+cat >/run/systemd/system/systemd-pcrextend.socket.d/50-no-condition.conf <<EOF
+[Unit]
+ConditionSecurity=
+EOF
+systemctl daemon-reload
+systemctl restart systemd-pcrextend.socket
+
+# Prepare a fresh LUKS2 volume unlocked by a passphrase keyfile
+IMAGE="$(mktemp /tmp/systemd-cryptsetup-measure-XXX.IMAGE)"
+truncate -s 20M "$IMAGE"
+echo -n passphrase >/tmp/passphrase
+chmod 0600 /tmp/passphrase
+cryptsetup luksFormat -q --pbkdf pbkdf2 --pbkdf-force-iterations 1000 --use-urandom "$IMAGE" /tmp/passphrase
+
+UUID="$(cryptsetup luksUUID "$IMAGE")"
+
+# Extract the raw volume key so we can recompute the expected HMAC below. The
+# volume key is measured as HMAC(volume_key, prefix) rather than a plain hash
+# (see cryptsetup_get_volume_key_prefix()/cryptsetup_get_volume_key_id()).
+cryptsetup luksDump -q --dump-volume-key --volume-key-file=/tmp/vk --key-file=/tmp/passphrase "$IMAGE"
+VK_HEX="$(od -An -v -tx1 /tmp/vk | tr -d ' \n')"
+
+# prefix = "cryptsetup:" <escaped volume name> ":" <LUKS UUID>; "test-volume"
+# contains no ':' so it is unescaped.
+PREFIX="cryptsetup:test-volume:$UUID"
+
+# Expected measured digest for the sha256 bank: HMAC-SHA256(volume_key, prefix)
+printf '%s' "$PREFIX" | openssl dgst -binary -sha256 -mac HMAC -macopt "hexkey:$VK_HEX" >/tmp/vk-hmac.bin
+DIGEST_EXPECTED="$(od -An -v -tx1 /tmp/vk-hmac.bin | tr -d ' \n')"
+
+# Remember the current event log length so we can index the record we add.
+# (json-seq: each record is RS(0x1e)-prefixed, LF-suffixed.) The log is created
+# lazily on the first measurement, and this subtest may be the first thing to
+# measure (e.g. when run in isolation), so treat an absent log as zero records.
+RECORD_COUNT=0
+if [[ -f /run/log/systemd/tpm2-measure.log ]]; then
+    RECORD_COUNT="$(jq --seq --slurp '. | length' </run/log/systemd/tpm2-measure.log | tr -d '\036')"
+fi
+
+tpm2_pcrread sha256:15 -Q -o /tmp/oldpcr15
+
+# Activate with measurement enabled. Unlock is via the keyfile (no TPM unlock),
+# to prove measurement is independent of the unlock mechanism.
+SYSTEMD_FORCE_MEASURE=1 systemd-cryptsetup attach test-volume "$IMAGE" /tmp/passphrase \
+    tpm2-measure-pcr=15,headless=1
+
+tpm2_pcrread sha256:15 -Q -o /tmp/newpcr15
+
+# The TPM PCR 15 must have been extended with the HMAC:
+#   new = sha256(old || HMAC(volume_key, prefix))
+diff /tmp/newpcr15 \
+     <(cat /tmp/oldpcr15 /tmp/vk-hmac.bin | openssl dgst -binary -sha256)
+
+# The volume-key measurement is the record we just added (the first one past RECORD_COUNT).
+test "$(jq --seq --slurp ".[$RECORD_COUNT].pcr" </run/log/systemd/tpm2-measure.log)" == "$(printf '\x1e15')"
+DIGEST_CURRENT="$(jq --seq --slurp --raw-output ".[$RECORD_COUNT].digests[] | select(.hashAlg == \"sha256\").digest" </run/log/systemd/tpm2-measure.log)"
+test "$DIGEST_CURRENT" == "$DIGEST_EXPECTED"
+
+systemd-cryptsetup detach test-volume
+
+# The deprecated tpm2-measure-bank= option must warn but not fail.
+SYSTEMD_FORCE_MEASURE=1 systemd-cryptsetup attach test-volume "$IMAGE" /tmp/passphrase \
+    tpm2-measure-pcr=15,tpm2-measure-bank=sha256,headless=1 |& tee /tmp/measure-bank.log
+systemd-cryptsetup detach test-volume
+grep -i "deprecated" /tmp/measure-bank.log >/dev/null