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cryptsetup: measure via the pcrextend varlink service

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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>
This commit is contained in:
Paul Meyer
2026-07-28 14:59:02 +02:00
parent 1812d8792f
commit 1bdf2db6f7
6 changed files with 138 additions and 101 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/cryptsetup/cryptsetup.c
+11 -94
View File
@@ -7,12 +7,10 @@
#include "sd-device.h"
#include "sd-event.h"
#include "sd-json.h"
#include "sd-messages.h"
#include "alloc-util.h"
#include "ask-password-api.h"
#include "build.h"
#include "crypto-util.h"
#include "cryptsetup-fido2.h"
#include "cryptsetup-keyfile.h"
#include "cryptsetup-pkcs11.h"
@@ -40,6 +38,7 @@
#include "options.h"
#include "parse-util.h"
#include "path-util.h"
#include "pcrextend-util.h"
#include "pkcs11-util.h"
#include "pretty-print.h"
#include "process-util.h"
@@ -123,7 +122,6 @@ static bool arg_tpm2_pin = false;
static char *arg_tpm2_pcrlock = NULL;
static usec_t arg_token_timeout_usec = 30*USEC_PER_SEC;
static unsigned arg_tpm2_measure_pcr = UINT_MAX; /* This and the following field is about measuring the unlocked volume key to the local TPM */
static char **arg_tpm2_measure_banks = NULL;
static char *arg_tpm2_measure_keyslot_nvpcr = NULL;
static char *arg_link_keyring = NULL;
static char *arg_link_key_type = NULL;
@@ -140,7 +138,6 @@ STATIC_DESTRUCTOR_REGISTER(arg_fido2_cid, freep);
STATIC_DESTRUCTOR_REGISTER(arg_fido2_rp_id, freep);
STATIC_DESTRUCTOR_REGISTER(arg_tpm2_device, freep);
STATIC_DESTRUCTOR_REGISTER(arg_tpm2_signature, freep);
STATIC_DESTRUCTOR_REGISTER(arg_tpm2_measure_banks, strv_freep);
STATIC_DESTRUCTOR_REGISTER(arg_tpm2_measure_keyslot_nvpcr, freep);
STATIC_DESTRUCTOR_REGISTER(arg_tpm2_pcrlock, freep);
STATIC_DESTRUCTOR_REGISTER(arg_link_keyring, freep);
@@ -537,30 +534,9 @@ static int parse_one_option(const char *option) {
} else if ((val = startswith(option, "tpm2-measure-bank="))) {
#if HAVE_OPENSSL
_cleanup_strv_free_ char **l = NULL;
r = dlopen_libcrypto(LOG_ERR);
if (r < 0)
return r;
l = strv_split(val, ":");
if (!l)
return log_oom();
STRV_FOREACH(i, l) {
const EVP_MD *implementation;
implementation = sym_EVP_get_digestbyname(*i);
if (!implementation)
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Unknown bank '%s', refusing.", val);
if (strv_extend(&arg_tpm2_measure_banks, sym_EVP_MD_get0_name(implementation)) < 0)
return log_oom();
}
#else
log_error("Build lacks OpenSSL support, cannot measure to PCR banks, ignoring: %s", option);
#endif
/* Deprecated: the PCR banks to measure into are now chosen by systemd-pcrextend
* (it extends all suitable banks). Kept for compatibility, but ignored. */
log_warning("The tpm2-measure-bank= option is deprecated and has no effect, ignoring.");
} else if ((val = startswith(option, "tpm2-measure-keyslot-nvpcr="))) {
@@ -1041,57 +1017,21 @@ static int measure_volume_key(
return 0;
}
#if HAVE_TPM2
_cleanup_(tpm2_context_unrefp) Tpm2Context *c = NULL;
r = tpm2_context_new_or_warn(arg_tpm2_device, &c);
if (r < 0)
return r;
_cleanup_strv_free_ char **l = NULL;
if (strv_isempty(arg_tpm2_measure_banks)) {
r = tpm2_get_good_pcr_banks_strv(c, UINT32_C(1) << arg_tpm2_measure_pcr, &l);
if (r < 0)
return log_error_errno(r, "Could not verify pcr banks: %m");
}
_cleanup_free_ char *joined = strv_join(l ?: arg_tpm2_measure_banks, ", ");
if (!joined)
return log_oom();
/* Note: we don't directly measure the volume key, it might be a security problem to send an
* unprotected direct hash of the secret volume key over the wire to the TPM. Hence let's instead
* send a HMAC signature instead. */
_cleanup_free_ char *prefix = NULL;
/* Note: what is extended to the SHA256 bank here must match the expected hash of 'fixate-volume-key='
* calculated by cryptsetup_get_volume_key_id(). */
r = cryptsetup_get_volume_key_prefix(cd, name, &prefix);
if (r)
return log_error_errno(r, "Could not verify pcr banks: %m");
if (r < 0)
return log_error_errno(r, "Failed to get volume key prefix: %m");
r = tpm2_pcr_extend_bytes(
c,
/* banks= */ l ?: arg_tpm2_measure_banks,
/* pcr_index = */ arg_tpm2_measure_pcr,
/* data = */ &IOVEC_MAKE_STRING(prefix),
/* secret = */ &IOVEC_MAKE(volume_key, volume_key_size),
/* event_type = */ TPM2_EVENT_VOLUME_KEY,
/* description = */ prefix);
/* Pass the volume key as HMAC secret. pcrextend extends HMAC(volume_key, prefix),
* never a bare hash. Matches cryptsetup_get_volume_key_id(). */
r = pcrextend_pcr_now(arg_tpm2_measure_pcr, prefix, &IOVEC_MAKE(volume_key, volume_key_size), "volume_key");
if (r < 0)
return log_error_errno(r, "Could not extend PCR: %m");
log_struct(LOG_INFO,
LOG_MESSAGE_ID(SD_MESSAGE_TPM_PCR_EXTEND_STR),
LOG_MESSAGE("Successfully extended PCR index %u with '%s' and volume key (banks %s).", arg_tpm2_measure_pcr, prefix, joined),
LOG_ITEM("MEASURING=%s", prefix),
LOG_ITEM("PCR=%u", arg_tpm2_measure_pcr),
LOG_ITEM("BANKS=%s", joined));
return 0;
#else
return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "TPM2 support disabled, not measuring volume key.");
#endif
}
static int measure_keyslot(
@@ -1100,9 +1040,8 @@ static int measure_keyslot(
const char *mechanism,
int keyslot) {
#if HAVE_TPM2
int r;
#endif
assert(cd);
assert(name);
@@ -1111,7 +1050,6 @@ static int measure_keyslot(
return 0;
}
#if HAVE_TPM2
r = efi_measured_os(LOG_WARNING);
if (r < 0)
return r;
@@ -1120,11 +1058,6 @@ static int measure_keyslot(
return 0;
}
_cleanup_(tpm2_context_unrefp) Tpm2Context *c = NULL;
r = tpm2_context_new_or_warn(arg_tpm2_device, &c);
if (r < 0)
return r;
_cleanup_free_ char *escaped = NULL;
escaped = xescape(name, ":"); /* avoid ambiguity around ":" once we join things below */
if (!escaped)
@@ -1139,27 +1072,11 @@ static int measure_keyslot(
if (!s)
return log_oom();
r = tpm2_nvpcr_extend_bytes(
c,
/* session= */ NULL,
arg_tpm2_measure_keyslot_nvpcr,
&IOVEC_MAKE_STRING(s),
/* secret= */ NULL,
TPM2_EVENT_KEYSLOT,
s);
r = pcrextend_nvpcr_now(arg_tpm2_measure_keyslot_nvpcr, s, "keyslot");
if (r < 0)
return log_error_errno(r, "Could not extend NvPCR: %m");
log_struct(LOG_INFO,
"MESSAGE_ID=" SD_MESSAGE_TPM_NVPCR_EXTEND_STR,
LOG_MESSAGE("Successfully extended NvPCR index '%s' with '%s'.", arg_tpm2_measure_keyslot_nvpcr, s),
"MEASURING=%s", s,
"NVPCR=%s", arg_tpm2_measure_keyslot_nvpcr);
return 0;
#else
return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "TPM2 support disabled, not measuring keyslot.");
#endif
}
static int log_external_activation(int r, const char *volume) {
src/shared/pcrextend-util.c
+5 -2
View File
@@ -25,7 +25,7 @@
#include "tpm2-pcr.h"
#include "user-record.h"
static int pcrextend_pcr_now(unsigned pcr, const char *word, const struct iovec *secret, const char *event) {
int pcrextend_pcr_now(unsigned pcr, const char *word, const struct iovec *secret, const char *event) {
#if HAVE_TPM2
int r;
@@ -78,11 +78,14 @@ static int pcrextend_pcr_now(unsigned pcr, const char *word, const struct iovec
#endif
}
static int pcrextend_nvpcr_now(const char *nvpcr, const char *word, const char *event) {
int pcrextend_nvpcr_now(const char *nvpcr, const char *word, const char *event) {
#if HAVE_TPM2
int r;
assert(nvpcr);
assert(word);
_cleanup_(sd_varlink_unrefp) sd_varlink *vl = NULL;
r = sd_varlink_connect_address(&vl, "/run/systemd/io.systemd.PCRExtend");
if (r < 0)
src/shared/pcrextend-util.h
+3
View File
@@ -5,6 +5,9 @@
#include "forward.h"
int pcrextend_pcr_now(unsigned pcr, const char *word, const struct iovec *secret, const char *event);
int pcrextend_nvpcr_now(const char *nvpcr, const char *word, const char *event);
int pcrextend_file_system_word(const char *path, char **ret, char **ret_normalized_path);
int pcrextend_machine_id_word(char **ret);
int pcrextend_product_id_word(char **ret);