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cryptenroll/repart/creds: no longer default to binding against literal PCR 7

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PCR 7 covers the SecureBoot policy, in particular "dbx", i.e. the
denylist of bad actors. That list is pretty much as frequently updated
as firmware these days (as fwupd took over automatic updating). This
means literal PCR 7 policies are problematic: they likely break soon,
and are as brittle as any other literal PCR policies.

hence, pick safer defaults, i.e. exclude PCR 7 from the default mask.
This means the mask is now empty.

Generally, people should really switch to signed PCR policies covering
PCR 11, in combination with systemd-pcrlock for the other PCRs.
This commit is contained in:
Lennart Poettering
2025-01-30 10:32:26 +01:00
parent 0f477f1d0b
commit 4b840414be
10 changed files with 34 additions and 53 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/creds/creds.c
+1 -1
View File
@@ -1091,7 +1091,7 @@ static int parse_argv(int argc, char *argv[]) {
}
if (arg_tpm2_pcr_mask == UINT32_MAX)
arg_tpm2_pcr_mask = TPM2_PCR_MASK_DEFAULT;
arg_tpm2_pcr_mask = 0;
if (arg_tpm2_public_key_pcr_mask == UINT32_MAX)
arg_tpm2_public_key_pcr_mask = UINT32_C(1) << TPM2_PCR_KERNEL_BOOT;
src/cryptenroll/cryptenroll.c
+1 -13
View File
@@ -308,7 +308,7 @@ static int parse_argv(int argc, char *argv[]) {
{}
};
bool auto_hash_pcr_values = true, auto_public_key_pcr_mask = true, auto_pcrlock = true;
bool auto_public_key_pcr_mask = true, auto_pcrlock = true;
int c, r;
assert(argc >= 0);
@@ -530,7 +530,6 @@ static int parse_argv(int argc, char *argv[]) {
break;
case ARG_TPM2_PCRS:
auto_hash_pcr_values = false;
r = tpm2_parse_pcr_argument_append(optarg, &arg_tpm2_hash_pcr_values, &arg_tpm2_n_hash_pcr_values);
if (r < 0)
return r;
@@ -698,17 +697,6 @@ static int parse_argv(int argc, char *argv[]) {
assert(arg_tpm2_public_key_pcr_mask == 0);
arg_tpm2_public_key_pcr_mask = INDEX_TO_MASK(uint32_t, TPM2_PCR_KERNEL_BOOT);
}
if (auto_hash_pcr_values && !arg_tpm2_pcrlock) { /* Only lock to PCR 7 by default if no pcrlock policy is around (which is a better replacement) */
assert(arg_tpm2_n_hash_pcr_values == 0);
if (!GREEDY_REALLOC_APPEND(
arg_tpm2_hash_pcr_values,
arg_tpm2_n_hash_pcr_values,
&TPM2_PCR_VALUE_MAKE(TPM2_PCR_INDEX_DEFAULT, /* hash= */ 0, /* value= */ {}),
1))
return log_oom();
}
}
return 1;
src/cryptsetup/cryptsetup.c
+1 -1
View File
@@ -1862,7 +1862,7 @@ static int attach_luks_or_plain_or_bitlk_by_tpm2(
r = acquire_tpm2_key(
name,
arg_tpm2_device,
arg_tpm2_pcr_mask == UINT32_MAX ? TPM2_PCR_MASK_DEFAULT : arg_tpm2_pcr_mask,
arg_tpm2_pcr_mask == UINT32_MAX ? TPM2_PCR_MASK_DEFAULT_LEGACY : arg_tpm2_pcr_mask,
UINT16_MAX,
/* pubkey= */ NULL,
/* pubkey_pcr_mask= */ 0,
src/repart/repart.c
+1 -13
View File
@@ -8012,7 +8012,7 @@ static int parse_argv(int argc, char *argv[], X509 **ret_certificate, EVP_PKEY *
_cleanup_(X509_freep) X509 *certificate = NULL;
_cleanup_(openssl_ask_password_ui_freep) OpenSSLAskPasswordUI *ui = NULL;
_cleanup_(EVP_PKEY_freep) EVP_PKEY *private_key = NULL;
bool auto_hash_pcr_values = true, auto_public_key_pcr_mask = true, auto_pcrlock = true;
bool auto_public_key_pcr_mask = true, auto_pcrlock = true;
int c, r;
assert(argc >= 0);
@@ -8241,7 +8241,6 @@ static int parse_argv(int argc, char *argv[], X509 **ret_certificate, EVP_PKEY *
break;
case ARG_TPM2_PCRS:
auto_hash_pcr_values = false;
r = tpm2_parse_pcr_argument_append(optarg, &arg_tpm2_hash_pcr_values, &arg_tpm2_n_hash_pcr_values);
if (r < 0)
return r;
@@ -8517,17 +8516,6 @@ static int parse_argv(int argc, char *argv[], X509 **ret_certificate, EVP_PKEY *
arg_tpm2_public_key_pcr_mask = INDEX_TO_MASK(uint32_t, TPM2_PCR_KERNEL_BOOT);
}
if (auto_hash_pcr_values && !arg_tpm2_pcrlock) { /* Only lock to PCR 7 if no pcr policy is specified. */
assert(arg_tpm2_n_hash_pcr_values == 0);
if (!GREEDY_REALLOC_APPEND(
arg_tpm2_hash_pcr_values,
arg_tpm2_n_hash_pcr_values,
&TPM2_PCR_VALUE_MAKE(TPM2_PCR_INDEX_DEFAULT, /* hash= */ 0, /* value= */ {}),
1))
return log_oom();
}
if (arg_pretty < 0 && isatty_safe(STDOUT_FILENO))
arg_pretty = true;
src/shared/tpm2-util.h
+6 -3
View File
@@ -394,9 +394,12 @@ int tpm2_parse_pcr_json_array(sd_json_variant *v, uint32_t *ret);
int tpm2_make_luks2_json(int keyslot, uint32_t hash_pcr_mask, uint16_t pcr_bank, const struct iovec *pubkey, uint32_t pubkey_pcr_mask, uint16_t primary_alg, const struct iovec blobs[], size_t n_blobs, const struct iovec policy_hash[], size_t n_policy_hash, const struct iovec *salt, const struct iovec *srk, const struct iovec *pcrlock_nv, TPM2Flags flags, sd_json_variant **ret);
int tpm2_parse_luks2_json(sd_json_variant *v, int *ret_keyslot, uint32_t *ret_hash_pcr_mask, uint16_t *ret_pcr_bank, struct iovec *ret_pubkey, uint32_t *ret_pubkey_pcr_mask, uint16_t *ret_primary_alg, struct iovec **ret_blobs, size_t *ret_n_blobs, struct iovec **ret_policy_hash, size_t *ret_n_policy_hash, struct iovec *ret_salt, struct iovec *ret_srk, struct iovec *ret_pcrlock_nv, TPM2Flags *ret_flags);
/* Default to PCR 7 only */
#define TPM2_PCR_INDEX_DEFAULT UINT32_C(7)
#define TPM2_PCR_MASK_DEFAULT INDEX_TO_MASK(uint32_t, TPM2_PCR_INDEX_DEFAULT)
/* Before v258 we used to bind to PCR 7 by default at various places if no explicit PCR mask was set. With
* v258 we stopped doing that (since the SecureBoot DB is as much subject to regular updates by tools such as
* fwupd as the firmware itself), but when unlocking to maintain compatibility when no mask is specified we
* still need to default to PCR 7. */
#define TPM2_PCR_INDEX_DEFAULT_LEGACY TPM2_PCR_SECURE_BOOT_POLICY
#define TPM2_PCR_MASK_DEFAULT_LEGACY INDEX_TO_MASK(uint32_t, TPM2_PCR_INDEX_DEFAULT_LEGACY)
/* We want the helpers below to work also if TPM2 libs are not available, hence define these four defines if
* they are missing. */