cryptenroll-tpm2.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include "alloc-util.h"
#include "ask-password-api.h"
#include "cryptenroll-tpm2.h"
#include "cryptsetup-tpm2.h"
#include "env-util.h"
#include "errno-util.h"
#include "fileio.h"
#include "hexdecoct.h"
#include "json.h"
#include "log.h"
#include "memory-util.h"
#include "random-util.h"
#include "sha256.h"
#include "tpm2-util.h"

static int search_policy_hash(
                struct crypt_device *cd,
                const void *hash,
                size_t hash_size) {

        int r;

        assert(cd);
        assert(hash || hash_size == 0);

        if (hash_size == 0)
                return 0;

        for (int token = 0; token < sym_crypt_token_max(CRYPT_LUKS2); token++) {
                _cleanup_(json_variant_unrefp) JsonVariant *v = NULL;
                _cleanup_free_ void *thash = NULL;
                size_t thash_size = 0;
                int keyslot;
                JsonVariant *w;

                r = cryptsetup_get_token_as_json(cd, token, "systemd-tpm2", &v);
                if (IN_SET(r, -ENOENT, -EINVAL, -EMEDIUMTYPE))
                        continue;
                if (r < 0)
                        return log_error_errno(r, "Failed to read JSON token data off disk: %m");

                keyslot = cryptsetup_get_keyslot_from_token(v);
                if (keyslot < 0) {
                        /* Handle parsing errors of the keyslots field gracefully, since it's not 'owned' by
                         * us, but by the LUKS2 spec */
                        log_warning_errno(keyslot, "Failed to determine keyslot of JSON token %i, skipping: %m", token);
                        continue;
                }

                w = json_variant_by_key(v, "tpm2-policy-hash");
                if (!w || !json_variant_is_string(w))
                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
                                               "TPM2 token data lacks 'tpm2-policy-hash' field.");

                r = unhexmem(json_variant_string(w), &thash, &thash_size);
                if (r < 0)
                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
                                               "Invalid base64 data in 'tpm2-policy-hash' field.");

                if (memcmp_nn(hash, hash_size, thash, thash_size) == 0)
                        return keyslot; /* Found entry with same hash. */
        }

        return -ENOENT; /* Not found */
}

static int get_pin(char **ret_pin_str, TPM2Flags *ret_flags) {
        _cleanup_(erase_and_freep) char *pin_str = NULL;
        TPM2Flags flags = 0;
        int r;

        assert(ret_pin_str);
        assert(ret_flags);

        r = getenv_steal_erase("NEWPIN", &pin_str);
        if (r < 0)
                return log_error_errno(r, "Failed to acquire PIN from environment: %m");
        if (r > 0)
                flags |= TPM2_FLAGS_USE_PIN;
        else {
                for (size_t i = 5;; i--) {
                        _cleanup_strv_free_erase_ char **pin = NULL, **pin2 = NULL;

                        if (i <= 0)
                                return log_error_errno(
                                                SYNTHETIC_ERRNO(ENOKEY), "Too many attempts, giving up.");

                        AskPasswordRequest req = {
                                .message = "Please enter TPM2 PIN:",
                                .icon = "drive-harddisk",
                                .keyring = "tpm2-pin",
                                .credential = "cryptenroll.new-tpm2-pin",
                        };

                        pin = strv_free_erase(pin);
                        r = ask_password_auto(
                                        &req,
                                        /* until= */ USEC_INFINITY,
                                        /* flags= */ 0,
                                        &pin);
                        if (r < 0)
                                return log_error_errno(r, "Failed to ask for user pin: %m");
                        assert(strv_length(pin) == 1);

                        req.message = "Please enter TPM2 PIN (repeat):";

                        r = ask_password_auto(
                                        &req,
                                        USEC_INFINITY,
                                        /* flags= */ 0,
                                        &pin2);
                        if (r < 0)
                                return log_error_errno(r, "Failed to ask for user pin: %m");
                        assert(strv_length(pin) == 1);

                        if (strv_equal(pin, pin2)) {
                                pin_str = strdup(*pin);
                                if (!pin_str)
                                        return log_oom();
                                flags |= TPM2_FLAGS_USE_PIN;
                                break;
                        }

                        log_error("PINs didn't match, please try again!");
                }
        }

        *ret_flags = flags;
        *ret_pin_str = TAKE_PTR(pin_str);

        return 0;
}

int load_volume_key_tpm2(
                struct crypt_device *cd,
                const char *cd_node,
                const char *device,
                void *ret_vk,
                size_t *ret_vks) {

        _cleanup_(iovec_done_erase) struct iovec decrypted_key = {};
        _cleanup_(erase_and_freep) char *passphrase = NULL;
        ssize_t passphrase_size;
        int r;

        assert_se(cd);
        assert_se(cd_node);
        assert_se(ret_vk);
        assert_se(ret_vks);

        bool found_some = false;
        int token = 0; /* first token to look at */

        for (;;) {
                _cleanup_(iovec_done) struct iovec pubkey = {}, salt = {}, srk = {}, pcrlock_nv = {};
                _cleanup_(iovec_done) struct iovec blob = {}, policy_hash = {};
                uint32_t hash_pcr_mask, pubkey_pcr_mask;
                uint16_t pcr_bank, primary_alg;
                TPM2Flags tpm2_flags;
                int keyslot;

                r = find_tpm2_auto_data(
                                cd,
                                UINT32_MAX,
                                token,
                                &hash_pcr_mask,
                                &pcr_bank,
                                &pubkey,
                                &pubkey_pcr_mask,
                                &primary_alg,
                                &blob,
                                &policy_hash,
                                &salt,
                                &srk,
                                &pcrlock_nv,
                                &tpm2_flags,
                                &keyslot,
                                &token);
                if (r == -ENXIO)
                        return log_full_errno(LOG_NOTICE,
                                              SYNTHETIC_ERRNO(EAGAIN),
                                              found_some
                                              ? "No TPM2 metadata matching the current system state found in LUKS2 header."
                                              : "No TPM2 metadata enrolled in LUKS2 header.");
                if (ERRNO_IS_NEG_NOT_SUPPORTED(r))
                        /* TPM2 support not compiled in? */
                        return log_debug_errno(SYNTHETIC_ERRNO(EAGAIN), "TPM2 support not available.");
                if (r < 0)
                        return r;

                found_some = true;

                r = acquire_tpm2_key(
                                cd_node,
                                device,
                                hash_pcr_mask,
                                pcr_bank,
                                &pubkey,
                                pubkey_pcr_mask,
                                /* signature_path= */ NULL,
                                /* pcrlock_path= */ NULL,
                                primary_alg,
                                /* key_file= */ NULL, /* key_file_size= */ 0, /* key_file_offset= */ 0, /* no key file */
                                &blob,
                                &policy_hash,
                                &salt,
                                &srk,
                                &pcrlock_nv,
                                tpm2_flags,
                                /* until= */ 0,
                                "cryptenroll.tpm2-pin",
                                /* askpw_flags= */ 0,
                                &decrypted_key);
                if (IN_SET(r, -EACCES, -ENOLCK))
                        return log_notice_errno(SYNTHETIC_ERRNO(EAGAIN), "TPM2 PIN unlock failed");
                if (r != -EPERM)
                        break;

                token++; /* try a different token next time */
        }

        if (r < 0)
                return log_error_errno(r, "Unlocking via TPM2 device failed: %m");

        passphrase_size = base64mem(decrypted_key.iov_base, decrypted_key.iov_len, &passphrase);
        if (passphrase_size < 0)
                return log_oom();

        r = crypt_volume_key_get(
                        cd,
                        CRYPT_ANY_SLOT,
                        ret_vk,
                        ret_vks,
                        passphrase,
                        passphrase_size);
        if (r < 0)
                return log_error_errno(r, "Unlocking via TPM2 device failed: %m");

        return r;
}

int enroll_tpm2(struct crypt_device *cd,
                const void *volume_key,
                size_t volume_key_size,
                const char *device,
                uint32_t seal_key_handle,
                const char *device_key,
                Tpm2PCRValue *hash_pcr_values,
                size_t n_hash_pcr_values,
                const char *pcr_pubkey_path,
                bool load_pcr_pubkey,
                uint32_t pubkey_pcr_mask,
                const char *signature_path,
                bool use_pin,
                const char *pcrlock_path,
                int *ret_slot_to_wipe) {

        _cleanup_(json_variant_unrefp) JsonVariant *v = NULL, *signature_json = NULL;
        _cleanup_(erase_and_freep) char *base64_encoded = NULL;
        _cleanup_(iovec_done) struct iovec srk = {}, blob = {}, pubkey = {};
        _cleanup_(iovec_done_erase) struct iovec secret = {};
        const char *node;
        _cleanup_(erase_and_freep) char *pin_str = NULL;
        ssize_t base64_encoded_size;
        int r, keyslot, slot_to_wipe = -1;
        TPM2Flags flags = 0;
        uint8_t binary_salt[SHA256_DIGEST_SIZE] = {};
        /*
         * erase the salt, we'd rather attempt to not have this in a coredump
         * as an attacker would have all the parameters but pin used to create
         * the session key. This problem goes away when we move to a trusted
         * primary key, aka the SRK.
         */
        CLEANUP_ERASE(binary_salt);

        assert(cd);
        assert(volume_key);
        assert(volume_key_size > 0);
        assert(tpm2_pcr_values_valid(hash_pcr_values, n_hash_pcr_values));
        assert(TPM2_PCR_MASK_VALID(pubkey_pcr_mask));
        assert(ret_slot_to_wipe);

        assert_se(node = crypt_get_device_name(cd));

        if (use_pin) {
                r = get_pin(&pin_str, &flags);
                if (r < 0)
                        return r;

                r = crypto_random_bytes(binary_salt, sizeof(binary_salt));
                if (r < 0)
                        return log_error_errno(r, "Failed to acquire random salt: %m");

                uint8_t salted_pin[SHA256_DIGEST_SIZE] = {};
                CLEANUP_ERASE(salted_pin);
                r = tpm2_util_pbkdf2_hmac_sha256(pin_str, strlen(pin_str), binary_salt, sizeof(binary_salt), salted_pin);
                if (r < 0)
                        return log_error_errno(r, "Failed to perform PBKDF2: %m");

                pin_str = erase_and_free(pin_str);
                /* re-stringify pin_str */
                base64_encoded_size = base64mem(salted_pin, sizeof(salted_pin), &pin_str);
                if (base64_encoded_size < 0)
                        return log_error_errno(base64_encoded_size, "Failed to base64 encode salted pin: %m");
        }

        TPM2B_PUBLIC public = {};
        /* Load the PCR public key if specified explicitly, or if no pcrlock policy was specified and
         * automatic loading of PCR public keys wasn't disabled explicitly. The reason we turn this off when
         * pcrlock is configured is simply that we currently not support both in combination. */
        if (pcr_pubkey_path || (load_pcr_pubkey && !pcrlock_path)) {
                r = tpm2_load_pcr_public_key(pcr_pubkey_path, &pubkey.iov_base, &pubkey.iov_len);
                if (r < 0) {
                        if (pcr_pubkey_path || signature_path || r != -ENOENT)
                                return log_error_errno(r, "Failed to read TPM PCR public key: %m");

                        log_debug_errno(r, "Failed to read TPM2 PCR public key, proceeding without: %m");
                        pubkey_pcr_mask = 0;
                } else {
                        r = tpm2_tpm2b_public_from_pem(pubkey.iov_base, pubkey.iov_len, &public);
                        if (r < 0)
                                return log_error_errno(r, "Could not convert public key to TPM2B_PUBLIC: %m");

                        if (signature_path) {
                                /* Also try to load the signature JSON object, to verify that our enrollment will work.
                                 * This is optional however, skip it if it's not explicitly provided. */

                                r = tpm2_load_pcr_signature(signature_path, &signature_json);
                                if (r < 0)
                                        return log_debug_errno(r, "Failed to read TPM PCR signature: %m");
                        }
                }
        } else
                pubkey_pcr_mask = 0;

        bool any_pcr_value_specified = tpm2_pcr_values_has_any_values(hash_pcr_values, n_hash_pcr_values);

        _cleanup_(tpm2_pcrlock_policy_done) Tpm2PCRLockPolicy pcrlock_policy = {};
        if (pcrlock_path) {
                r = tpm2_pcrlock_policy_load(pcrlock_path, &pcrlock_policy);
                if (r < 0)
                        return r;

                any_pcr_value_specified = true;
                flags |= TPM2_FLAGS_USE_PCRLOCK;
        }

        _cleanup_(tpm2_context_unrefp) Tpm2Context *tpm2_context = NULL;
        TPM2B_PUBLIC device_key_public = {};
        if (device_key) {
                r = tpm2_load_public_key_file(device_key, &device_key_public);
                if (r < 0)
                        return r;

                if (!tpm2_pcr_values_has_all_values(hash_pcr_values, n_hash_pcr_values))
                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
                                               "Must provide all PCR values when using TPM2 device key.");
        } else {
                r = tpm2_context_new_or_warn(device, &tpm2_context);
                if (r < 0)
                        return r;

                if (!tpm2_pcr_values_has_all_values(hash_pcr_values, n_hash_pcr_values)) {
                        r = tpm2_pcr_read_missing_values(tpm2_context, hash_pcr_values, n_hash_pcr_values);
                        if (r < 0)
                                return log_error_errno(r, "Could not read pcr values: %m");
                }
        }

        uint16_t hash_pcr_bank = 0;
        uint32_t hash_pcr_mask = 0;
        if (n_hash_pcr_values > 0) {
                size_t hash_count;
                r = tpm2_pcr_values_hash_count(hash_pcr_values, n_hash_pcr_values, &hash_count);
                if (r < 0)
                        return log_error_errno(r, "Could not get hash count: %m");

                if (hash_count > 1)
                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Multiple PCR banks selected.");

                hash_pcr_bank = hash_pcr_values[0].hash;
                r = tpm2_pcr_values_to_mask(hash_pcr_values, n_hash_pcr_values, hash_pcr_bank, &hash_pcr_mask);
                if (r < 0)
                        return log_error_errno(r, "Could not get hash mask: %m");
        }

        TPM2B_DIGEST policy = TPM2B_DIGEST_MAKE(NULL, TPM2_SHA256_DIGEST_SIZE);
        r = tpm2_calculate_sealing_policy(
                        hash_pcr_values,
                        n_hash_pcr_values,
                        iovec_is_set(&pubkey) ? &public : NULL,
                        use_pin,
                        pcrlock_path ? &pcrlock_policy : NULL,
                        &policy);
        if (r < 0)
                return r;

        if (device_key)
                r = tpm2_calculate_seal(
                                seal_key_handle,
                                &device_key_public,
                                /* attributes= */ NULL,
                                /* secret= */ NULL,
                                &policy,
                                pin_str,
                                &secret,
                                &blob,
                                &srk);
        else
                r = tpm2_seal(tpm2_context,
                              seal_key_handle,
                              &policy,
                              pin_str,
                              &secret,
                              &blob,
                              /* ret_primary_alg= */ NULL,
                              &srk);
        if (r < 0)
                return log_error_errno(r, "Failed to seal to TPM2: %m");

        /* Let's see if we already have this specific PCR policy hash enrolled, if so, exit early. */
        r = search_policy_hash(cd, policy.buffer, policy.size);
        if (r == -ENOENT)
                log_debug_errno(r, "PCR policy hash not yet enrolled, enrolling now.");
        else if (r < 0)
                return r;
        else if (use_pin) {
                log_debug("This PCR set is already enrolled, re-enrolling anyway to update PIN.");
                slot_to_wipe = r;
        } else {
                log_info("This PCR set is already enrolled, executing no operation.");
                *ret_slot_to_wipe = slot_to_wipe;
                return r; /* return existing keyslot, so that wiping won't kill it */
        }

        /* If possible, verify the sealed data object. */
        if ((!iovec_is_set(&pubkey) || signature_json) && !any_pcr_value_specified && !device_key) {
                _cleanup_(iovec_done_erase) struct iovec secret2 = {};

                log_debug("Unsealing for verification...");
                r = tpm2_unseal(tpm2_context,
                                hash_pcr_mask,
                                hash_pcr_bank,
                                &pubkey,
                                pubkey_pcr_mask,
                                signature_json,
                                pin_str,
                                pcrlock_path ? &pcrlock_policy : NULL,
                                /* primary_alg= */ 0,
                                &blob,
                                &IOVEC_MAKE(policy.buffer, policy.size),
                                &srk,
                                &secret2);
                if (r < 0)
                        return log_error_errno(r, "Failed to unseal secret using TPM2: %m");

                if (iovec_memcmp(&secret, &secret2) != 0)
                        return log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "TPM2 seal/unseal verification failed.");
        }

        /* let's base64 encode the key to use, for compat with homed (and it's easier to every type it in by keyboard, if that might end up being necessary. */
        base64_encoded_size = base64mem(secret.iov_base, secret.iov_len, &base64_encoded);
        if (base64_encoded_size < 0)
                return log_error_errno(base64_encoded_size, "Failed to base64 encode secret key: %m");

        r = cryptsetup_set_minimal_pbkdf(cd);
        if (r < 0)
                return log_error_errno(r, "Failed to set minimal PBKDF: %m");

        keyslot = crypt_keyslot_add_by_volume_key(
                        cd,
                        CRYPT_ANY_SLOT,
                        volume_key,
                        volume_key_size,
                        base64_encoded,
                        base64_encoded_size);
        if (keyslot < 0)
                return log_error_errno(keyslot, "Failed to add new TPM2 key to %s: %m", node);

        r = tpm2_make_luks2_json(
                        keyslot,
                        hash_pcr_mask,
                        hash_pcr_bank,
                        &pubkey,
                        pubkey_pcr_mask,
                        /* primary_alg= */ 0,
                        &blob,
                        &IOVEC_MAKE(policy.buffer, policy.size),
                        use_pin ? &IOVEC_MAKE(binary_salt, sizeof(binary_salt)) : NULL,
                        &srk,
                        pcrlock_path ? &pcrlock_policy.nv_handle : NULL,
                        flags,
                        &v);
        if (r < 0)
                return log_error_errno(r, "Failed to prepare TPM2 JSON token object: %m");

        r = cryptsetup_add_token_json(cd, v);
        if (r < 0)
                return log_error_errno(r, "Failed to add TPM2 JSON token to LUKS2 header: %m");

        log_info("New TPM2 token enrolled as key slot %i.", keyslot);

        *ret_slot_to_wipe = slot_to_wipe;
        return keyslot;
}