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Message-Id: <20220504161439.10.Ifce072ae1ef1ce39bd681fff55af13a054045d9f@changeid>
Date: Wed, 4 May 2022 16:21:02 -0700
From: Evan Green <evgreen@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: Matthew Garrett <mgarrett@...ora.tech>, dlunev@...gle.com,
zohar@...ux.ibm.com, jejb@...ux.ibm.com,
linux-integrity@...r.kernel.org, corbet@....net, rjw@...ysocki.net,
gwendal@...omium.org, jarkko@...nel.org, linux-pm@...r.kernel.org,
Evan Green <evgreen@...omium.org>, Hao Wu <hao.wu@...rik.com>,
Len Brown <len.brown@...el.com>,
Matthew Garrett <matthewgarrett@...gle.com>,
Pavel Machek <pavel@....cz>,
"Rafael J. Wysocki" <rafael@...nel.org>, axelj <axelj@...s.com>
Subject: [PATCH 10/10] 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.
Sourced-from: Matthew Garrett <mjg59@...gle.com>
Signed-off-by: Evan Green <evgreen@...omium.org>
---
The original version of this patch is here:
https://patchwork.kernel.org/project/linux-pm/patch/20210220013255.1083202-10-matthewgarrett@google.com/
include/linux/tpm.h | 4 +
kernel/power/snapenc.c | 163 +++++++++++++++++++++++++++++++++++++++--
2 files changed, 160 insertions(+), 7 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 38bc820f780d8b..9d140c62b49db1 100644
--- a/kernel/power/snapenc.c
+++ b/kernel/power/snapenc.c
@@ -495,6 +495,111 @@ 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);
+
+ /* Policy type - session */
+ 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(int) + sizeof(u16) + sizeof(nonce)) {
+ rc = -EINVAL;
+ goto out;
+ }
+
+ *session_handle = be32_to_cpu(*(int *)&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;
@@ -554,7 +659,11 @@ static int snapshot_create_kernel_key(struct snapshot_data *data)
struct key *key;
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)
@@ -584,13 +693,35 @@ static int snapshot_create_kernel_key(struct snapshot_data *data)
if (ret != 0)
goto reset;
+ policydigest = kmalloc(SHA256_DIGEST_SIZE * 2 + 1, GFP_KERNEL);
+ if (!policydigest) {
+ ret = -ENOMEM;
+ goto reset;
+ }
+
+ ret = tpm_setup_policy(chip, &session_handle);
+ if (ret != 0)
+ goto reset;
+
+ ret = tpm_policy_get_digest(chip, session_handle, policy);
+ if (ret != 0)
+ goto flush;
+
+ bin2hex(policydigest, policy, SHA256_DIGEST_SIZE);
+ policydigest[SHA256_DIGEST_SIZE * 2] = '\0';
+ keyinfo = kasprintf(GFP_KERNEL, keytemplate, policydigest);
+ if (!keyinfo) {
+ ret = -ENOMEM;
+ goto flush;
+ }
+
key = key_alloc(&key_type_trusted, "swsusp", GLOBAL_ROOT_UID,
GLOBAL_ROOT_GID, cred, 0, KEY_ALLOC_NOT_IN_QUOTA,
NULL);
if (IS_ERR(key)) {
ret = PTR_ERR(key);
- goto reset;
+ goto flush;
}
ret = key_instantiate_and_link(key, keyinfo, strlen(keyinfo) + 1, NULL,
@@ -606,8 +737,14 @@ static int snapshot_create_kernel_key(struct snapshot_data *data)
key_revoke(key);
key_put(key);
}
+
+flush:
+ tpm2_flush_context(chip, session_handle);
+
reset:
kfree(digests);
+ kfree(keyinfo);
+ kfree(policydigest);
tpm_pcr_reset(chip, 23);
return ret;
}
@@ -669,13 +806,14 @@ 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;
struct trusted_key_payload *payload;
+ int session_handle = -1;
int i, ret;
chip = tpm_default_chip();
@@ -706,17 +844,24 @@ static int snapshot_load_kernel_key(struct snapshot_data *data,
if (ret != 0)
goto reset;
- blobstring = kmalloc(blob->blob_len * 2, GFP_KERNEL);
+ ret = tpm_setup_policy(chip, &session_handle);
+ if (ret != 0)
+ goto reset;
+
+ blobstring = kmalloc(blob->blob_len * 2 + 1, GFP_KERNEL);
if (!blobstring) {
ret = -ENOMEM;
- goto reset;
+ goto flush;
}
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 reset;
+ goto flush;
}
key = key_alloc(&key_type_trusted, "swsusp", GLOBAL_ROOT_UID,
@@ -790,6 +935,10 @@ static int snapshot_load_kernel_key(struct snapshot_data *data,
key_revoke(key);
key_put(key);
}
+
+flush:
+ tpm2_flush_context(chip, session_handle);
+
reset:
kfree(keyinfo);
kfree(blobstring);
--
2.31.0
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