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Date: Tue, 27 Sep 2022 09:49:22 -0700
From: Evan Green <evgreen@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: linux-integrity@...r.kernel.org, apronin@...omium.org,
dlunev@...gle.com, jarkko@...nel.org, Pavel Machek <pavel@....cz>,
Ben Boeckel <me@...boeckel.net>, rjw@...ysocki.net,
corbet@....net, linux-pm@...r.kernel.org, zohar@...ux.ibm.com,
Kees Cook <keescook@...omium.org>,
Eric Biggers <ebiggers@...nel.org>, jejb@...ux.ibm.com,
gwendal@...omium.org, Matthew Garrett <mgarrett@...ora.tech>,
Evan Green <evgreen@...omium.org>,
Matthew Garrett <mjg59@...gle.com>, Hao Wu <hao.wu@...rik.com>,
Len Brown <len.brown@...el.com>,
Matthew Garrett <matthewgarrett@...gle.com>,
"Rafael J. Wysocki" <rafael@...nel.org>, axelj <axelj@...s.com>
Subject: [PATCH v3 11/11] PM: hibernate: seal the encryption key with a PCR policy
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@google.com/
Co-developed-by: Matthew Garrett <mjg59@...gle.com>
Signed-off-by: Matthew Garrett <mjg59@...gle.com>
Signed-off-by: Evan Green <evgreen@...omium.org>
---
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 | 164 ++++++++++++++++++++++++++++++++++++++++-
2 files changed, 164 insertions(+), 4 deletions(-)
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 438f8bc0a50582..cd520efc515bca 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 1f08942450775a..02d25f9500cb7f 100644
--- a/kernel/power/snapenc.c
+++ b/kernel/power/snapenc.c
@@ -433,6 +433,111 @@ 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;
@@ -492,7 +597,12 @@ static int snapshot_create_kernel_key(struct snapshot_data *data)
struct key *key = NULL;
int ret, i;
/* Create a key sealed by the SRK. */
- char *keyinfo = "new\t32\tkeyhandle=0x81000000\tcreationpcrs=0x00800000";
+ char *keyinfo = NULL;
+ const char *keytemplate =
+ "new\t32\tkeyhandle=0x81000000\tcreationpcrs=0x00800000\tpolicydigest=%s";
+ char policy[SHA256_DIGEST_SIZE];
+ char *policydigest = NULL;
+ int session_handle = -1;
chip = tpm_default_chip();
if (!chip)
@@ -524,6 +634,28 @@ 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);
@@ -548,7 +680,16 @@ 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);
tpm_pcr_reset(chip, 23);
out_dev:
@@ -613,13 +754,14 @@ static int snapshot_load_kernel_key(struct snapshot_data *data,
char certhash[SHA256_DIGEST_SIZE];
const struct cred *cred = current_cred();
- char *keytemplate = "load\t%s\tkeyhandle=0x81000000";
+ char *keytemplate = "load\t%s\tkeyhandle=0x81000000\tpolicyhandle=0x%x";
struct tpm_digest *digests = NULL;
char *blobstring = NULL;
char *keyinfo = NULL;
struct tpm_chip *chip;
struct key *key = NULL;
struct trusted_key_payload *payload;
+ int session_handle = -1;
int i, ret;
chip = tpm_default_chip();
@@ -652,14 +794,21 @@ 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;
@@ -742,6 +891,13 @@ 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);
--
2.31.0
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