The key blob is not secret, and by default the TPM will happily unseal it regardless of system state. We can protect against that by sealing the secret with a PCR policy - if the current PCR state doesn't match, the TPM will refuse to release the secret. For now let's just seal it to PCR 23. In the long term we may want a more flexible policy around this, such as including PCR 7 for PCs or 0 for Chrome OS. Link: https://lore.kernel.org/all/20210220013255.1083202-10-matthewgarrett@xxxxxxxxxx/ Co-developed-by: Matthew Garrett <mjg59@xxxxxxxxxx> Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxx> Signed-off-by: Evan Green <evgreen@xxxxxxxxxxxx> --- Changes in v4: - Local variable ordering (Jarkko) Changes in v3: - Changed funky tag to Co-developed-by (Kees) Changes in v2: - Fix sparse warnings - Fix session type comment (Andrey) - Eliminate extra label in get/create_kernel_key() (Andrey) - Call tpm_try_get_ops() before calling tpm2_flush_context(). include/linux/tpm.h | 4 + kernel/power/snapenc.c | 166 +++++++++++++++++++++++++++++++++++++++-- 2 files changed, 165 insertions(+), 5 deletions(-) diff --git a/include/linux/tpm.h b/include/linux/tpm.h index 9c2ee3e30ffa5d..252a8a92a7ff5b 100644 --- a/include/linux/tpm.h +++ b/include/linux/tpm.h @@ -233,18 +233,22 @@ enum tpm2_command_codes { TPM2_CC_CONTEXT_LOAD = 0x0161, TPM2_CC_CONTEXT_SAVE = 0x0162, TPM2_CC_FLUSH_CONTEXT = 0x0165, + TPM2_CC_START_AUTH_SESSION = 0x0176, TPM2_CC_VERIFY_SIGNATURE = 0x0177, TPM2_CC_GET_CAPABILITY = 0x017A, TPM2_CC_GET_RANDOM = 0x017B, TPM2_CC_PCR_READ = 0x017E, + TPM2_CC_POLICY_PCR = 0x017F, TPM2_CC_PCR_EXTEND = 0x0182, TPM2_CC_EVENT_SEQUENCE_COMPLETE = 0x0185, TPM2_CC_HASH_SEQUENCE_START = 0x0186, + TPM2_CC_POLICY_GET_DIGEST = 0x0189, TPM2_CC_CREATE_LOADED = 0x0191, TPM2_CC_LAST = 0x0193, /* Spec 1.36 */ }; enum tpm2_permanent_handles { + TPM2_RH_NULL = 0x40000007, TPM2_RS_PW = 0x40000009, }; diff --git a/kernel/power/snapenc.c b/kernel/power/snapenc.c index 2f421061498246..23f4d09ced578b 100644 --- a/kernel/power/snapenc.c +++ b/kernel/power/snapenc.c @@ -438,6 +438,111 @@ void snapshot_teardown_encryption(struct snapshot_data *data) memset(data->user_key, 0, sizeof(data->user_key)); } +static int tpm_setup_policy(struct tpm_chip *chip, int *session_handle) +{ + struct tpm_header *head; + struct tpm_buf buf; + char nonce[32] = {0x00}; + int rc; + + rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, + TPM2_CC_START_AUTH_SESSION); + if (rc) + return rc; + + /* Decrypt key */ + tpm_buf_append_u32(&buf, TPM2_RH_NULL); + + /* Auth entity */ + tpm_buf_append_u32(&buf, TPM2_RH_NULL); + + /* Nonce - blank is fine here */ + tpm_buf_append_u16(&buf, sizeof(nonce)); + tpm_buf_append(&buf, nonce, sizeof(nonce)); + + /* Encrypted secret - empty */ + tpm_buf_append_u16(&buf, 0); + + /* Session type - policy */ + tpm_buf_append_u8(&buf, 0x01); + + /* Encryption type - NULL */ + tpm_buf_append_u16(&buf, TPM_ALG_NULL); + + /* Hash type - SHA256 */ + tpm_buf_append_u16(&buf, TPM_ALG_SHA256); + + rc = tpm_send(chip, buf.data, tpm_buf_length(&buf)); + if (rc) + goto out; + + head = (struct tpm_header *)buf.data; + if (be32_to_cpu(head->length) != sizeof(struct tpm_header) + + sizeof(u32) + sizeof(u16) + sizeof(nonce)) { + rc = -EINVAL; + goto out; + } + + *session_handle = be32_to_cpu(*(__be32 *)&buf.data[10]); + memcpy(nonce, &buf.data[16], sizeof(nonce)); + tpm_buf_destroy(&buf); + rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_POLICY_PCR); + if (rc) + return rc; + + tpm_buf_append_u32(&buf, *session_handle); + + /* PCR digest - read from the PCR, we'll verify creation data later */ + tpm_buf_append_u16(&buf, 0); + + /* One PCR */ + tpm_buf_append_u32(&buf, 1); + + /* SHA256 banks */ + tpm_buf_append_u16(&buf, TPM_ALG_SHA256); + + /* Select PCR 23 */ + tpm_buf_append_u32(&buf, 0x03000080); + rc = tpm_send(chip, buf.data, tpm_buf_length(&buf)); + if (rc) + goto out; + +out: + tpm_buf_destroy(&buf); + return rc; +} + +static int tpm_policy_get_digest(struct tpm_chip *chip, int handle, + char *digest) +{ + struct tpm_header *head; + struct tpm_buf buf; + int rc; + + rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_POLICY_GET_DIGEST); + if (rc) + return rc; + + tpm_buf_append_u32(&buf, handle); + rc = tpm_send(chip, buf.data, tpm_buf_length(&buf)); + + if (rc) + goto out; + + head = (struct tpm_header *)buf.data; + if (be32_to_cpu(head->length) != sizeof(struct tpm_header) + + sizeof(u16) + SHA256_DIGEST_SIZE) { + rc = -EINVAL; + goto out; + } + + memcpy(digest, &buf.data[12], SHA256_DIGEST_SIZE); + +out: + tpm_buf_destroy(&buf); + return rc; +} + static int snapshot_setup_encryption_common(struct snapshot_data *data) { int i, rc; @@ -492,11 +597,16 @@ static int snapshot_setup_encryption_common(struct snapshot_data *data) static int snapshot_create_kernel_key(struct snapshot_data *data) { /* Create a key sealed by the SRK. */ - char *keyinfo = "new\t32\tkeyhandle=0x81000000\tcreationpcrs=0x00800000"; + const char *keytemplate = + "new\t32\tkeyhandle=0x81000000\tcreationpcrs=0x00800000\tpolicydigest=%s"; const struct cred *cred = current_cred(); struct tpm_digest *digests = NULL; + char policy[SHA256_DIGEST_SIZE]; + char *policydigest = NULL; + int session_handle = -1; struct key *key = NULL; struct tpm_chip *chip; + char *keyinfo = NULL; int ret, i; chip = tpm_default_chip(); @@ -529,6 +639,28 @@ static int snapshot_create_kernel_key(struct snapshot_data *data) if (ret != 0) goto out; + policydigest = kmalloc(SHA256_DIGEST_SIZE * 2 + 1, GFP_KERNEL); + if (!policydigest) { + ret = -ENOMEM; + goto out; + } + + ret = tpm_setup_policy(chip, &session_handle); + if (ret != 0) + goto out; + + ret = tpm_policy_get_digest(chip, session_handle, policy); + if (ret != 0) + goto out; + + bin2hex(policydigest, policy, SHA256_DIGEST_SIZE); + policydigest[SHA256_DIGEST_SIZE * 2] = '\0'; + keyinfo = kasprintf(GFP_KERNEL, keytemplate, policydigest); + if (!keyinfo) { + ret = -ENOMEM; + goto out; + } + key = key_alloc(&key_type_trusted, "swsusp", GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, 0, KEY_ALLOC_NOT_IN_QUOTA, NULL); @@ -539,7 +671,7 @@ static int snapshot_create_kernel_key(struct snapshot_data *data) goto out; } - ret = key_instantiate_and_link(key, keyinfo, sizeof(keyinfo), NULL, + ret = key_instantiate_and_link(key, keyinfo, strlen(keyinfo) + 1, NULL, NULL); if (ret != 0) goto out; @@ -553,7 +685,16 @@ static int snapshot_create_kernel_key(struct snapshot_data *data) key_put(key); } + if (session_handle != -1) { + if (tpm_try_get_ops(chip) == 0) { + tpm2_flush_context(chip, session_handle); + tpm_put_ops(chip); + } + } + kfree(digests); + kfree(keyinfo); + kfree(policydigest); tpm2_pcr_reset(chip, 23); out_dev: @@ -617,12 +758,13 @@ static int snapshot_load_kernel_key(struct snapshot_data *data, struct uswsusp_key_blob *blob) { - char *keytemplate = "load\t%s\tkeyhandle=0x81000000"; + char *keytemplate = "load\t%s\tkeyhandle=0x81000000\tpolicyhandle=0x%x"; const struct cred *cred = current_cred(); struct trusted_key_payload *payload; char certhash[SHA256_DIGEST_SIZE]; struct tpm_digest *digests = NULL; char *blobstring = NULL; + int session_handle = -1; struct key *key = NULL; struct tpm_chip *chip; char *keyinfo = NULL; @@ -658,14 +800,21 @@ static int snapshot_load_kernel_key(struct snapshot_data *data, if (ret != 0) goto out; - blobstring = kmalloc(blob->blob_len * 2, GFP_KERNEL); + ret = tpm_setup_policy(chip, &session_handle); + if (ret != 0) + goto out; + + blobstring = kmalloc(blob->blob_len * 2 + 1, GFP_KERNEL); if (!blobstring) { ret = -ENOMEM; goto out; } bin2hex(blobstring, blob->blob, blob->blob_len); - keyinfo = kasprintf(GFP_KERNEL, keytemplate, blobstring); + blobstring[blob->blob_len * 2] = '\0'; + keyinfo = kasprintf(GFP_KERNEL, keytemplate, blobstring, + session_handle); + if (!keyinfo) { ret = -ENOMEM; goto out; @@ -748,6 +897,13 @@ static int snapshot_load_kernel_key(struct snapshot_data *data, key_put(key); } + if (session_handle != -1) { + if (tpm_try_get_ops(chip) == 0) { + tpm2_flush_context(chip, session_handle); + tpm_put_ops(chip); + } + } + kfree(keyinfo); kfree(blobstring); kfree(digests); -- 2.38.1.431.g37b22c650d-goog
