[PATCH v5 08/11] PM: hibernate: Use TPM-backed keys to encrypt image

[Evan Green]

When using encrypted hibernate images, have the TPM create a key for us
and seal it. By handing back a sealed blob instead of the raw key, we
prevent usermode from being able to decrypt and tamper with the
hibernate image on a different machine.

We'll also go through the motions of having PCR23 set to a known value at
the time of key creation and unsealing. Currently there's nothing that
enforces the contents of PCR23 as a condition to unseal the key blob,
that will come in a later change.

Suggested-by: Matthew Garrett <mjg59@xxxxxxxxxx>
Signed-off-by: Evan Green <evgreen@xxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

---
Matthew's incarnation of this patch is at:
https://patchwork.kernel.org/project/linux-pm/patch/20210220013255.1083202-9-matthewgarrett@xxxxxxxxxx/

Changes in v5:
 - Use Suggested-by tag instead of made up Sourced-from (Kees)
 - ENCRYPTED_HIBERNATION should depend on TCG_TPM2_RESTRCT_PCR

Changes in v4:
 - s/tpm_pcr_reset/tpm2_pcr_reset/ due to change in other patch
 - Variable ordering and whitespace fixes (Jarkko)
 - Add NULL check explanation in teardown (Jarkko)
 - Change strlen+1 to sizeof for static buffer (Jarkko)
 - Fix nr_allocated_banks loop overflow (found via KASAN)

Changes in v3:
 - ENCRYPTED_HIBERNATION needs TRUSTED_KEYS builtin for
   key_type_trusted.
 - Remove KEYS dependency since it's covered by TRUSTED_KEYS (Kees)

Changes in v2:
 - Rework load/create_kernel_key() to eliminate a label (Andrey)
 - Call put_device() needed from calling tpm_default_chip().

 kernel/power/Kconfig   |   2 +
 kernel/power/snapenc.c | 211 +++++++++++++++++++++++++++++++++++++++--
 kernel/power/user.h    |   1 +
 3 files changed, 205 insertions(+), 9 deletions(-)

diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 2bde64bddae403..420024f46992b2 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -96,6 +96,8 @@ config ENCRYPTED_HIBERNATION
 	bool "Encryption support for userspace snapshots"
 	depends on HIBERNATION_SNAPSHOT_DEV
 	depends on CRYPTO_AEAD2=y
+	depends on TCG_TPM2_RESTRICT_PCR
+	depends on TRUSTED_KEYS=y
 	help
 	  Enable support for kernel-based encryption of hibernation snapshots
 	  created by uswsusp tools.
diff --git a/kernel/power/snapenc.c b/kernel/power/snapenc.c
index 0d055ea6203a5b..f1db4eddb3c34c 100644
--- a/kernel/power/snapenc.c
+++ b/kernel/power/snapenc.c
@@ -4,13 +4,23 @@
 #include <linux/crypto.h>
 #include <crypto/aead.h>
 #include <crypto/gcm.h>
+#include <keys/trusted-type.h>
+#include <linux/key-type.h>
 #include <linux/random.h>
 #include <linux/mm.h>
+#include <linux/tpm.h>
 #include <linux/uaccess.h>
 
 #include "power.h"
 #include "user.h"
 
+/* sha256("To sleep, perchance to dream") */
+static struct tpm_digest known_digest = { .alg_id = TPM_ALG_SHA256,
+	.digest = {0x92, 0x78, 0x3d, 0x79, 0x2d, 0x00, 0x31, 0xb0, 0x55, 0xf9,
+		   0x1e, 0x0d, 0xce, 0x83, 0xde, 0x1d, 0xc4, 0xc5, 0x8e, 0x8c,
+		   0xf1, 0x22, 0x38, 0x6c, 0x33, 0xb1, 0x14, 0xb7, 0xec, 0x05,
+		   0x5f, 0x49}};
+
 /* Encrypt more data from the snapshot into the staging area. */
 static int snapshot_encrypt_refill(struct snapshot_data *data)
 {
@@ -313,6 +323,16 @@ void snapshot_teardown_encryption(struct snapshot_data *data)
 {
 	int i;
 
+	/*
+	 * Do NULL checks so this function can safely be called from error paths
+	 * and other places where this context may not be fully set up.
+	 */
+	if (data->key) {
+		key_revoke(data->key);
+		key_put(data->key);
+		data->key = NULL;
+	}
+
 	if (data->aead_req) {
 		aead_request_free(data->aead_req);
 		data->aead_req = NULL;
@@ -381,10 +401,82 @@ static int snapshot_setup_encryption_common(struct snapshot_data *data)
 	return rc;
 }
 
+static int snapshot_create_kernel_key(struct snapshot_data *data)
+{
+	/* Create a key sealed by the SRK. */
+	char *keyinfo = "new\t32\tkeyhandle=0x81000000";
+	const struct cred *cred = current_cred();
+	struct tpm_digest *digests = NULL;
+	struct key *key = NULL;
+	struct tpm_chip *chip;
+	int ret, i;
+
+	chip = tpm_default_chip();
+	if (!chip)
+		return -ENODEV;
+
+	if (!(tpm_is_tpm2(chip))) {
+		ret = -ENODEV;
+		goto out_dev;
+	}
+
+	ret = tpm2_pcr_reset(chip, 23);
+	if (ret)
+		goto out;
+
+	digests = kcalloc(chip->nr_allocated_banks, sizeof(struct tpm_digest),
+			  GFP_KERNEL);
+	if (!digests) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	for (i = 0; i < chip->nr_allocated_banks; i++) {
+		digests[i].alg_id = chip->allocated_banks[i].alg_id;
+		if (digests[i].alg_id == known_digest.alg_id)
+			memcpy(&digests[i], &known_digest, sizeof(known_digest));
+	}
+
+	ret = tpm_pcr_extend(chip, 23, digests);
+	if (ret != 0)
+		goto out;
+
+	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);
+		key = NULL;
+		goto out;
+	}
+
+	ret = key_instantiate_and_link(key, keyinfo, sizeof(keyinfo), NULL,
+				       NULL);
+	if (ret != 0)
+		goto out;
+
+	data->key = key;
+	key = NULL;
+
+out:
+	if (key) {
+		key_revoke(key);
+		key_put(key);
+	}
+
+	kfree(digests);
+	tpm2_pcr_reset(chip, 23);
+
+out_dev:
+	put_device(&chip->dev);
+	return ret;
+}
+
 int snapshot_get_encryption_key(struct snapshot_data *data,
 				struct uswsusp_key_blob __user *key)
 {
-	u8 aead_key[SNAPSHOT_ENCRYPTION_KEY_SIZE];
+	struct trusted_key_payload *payload;
 	u8 nonce[USWSUSP_KEY_NONCE_SIZE];
 	int rc;
 
@@ -400,21 +492,28 @@ int snapshot_get_encryption_key(struct snapshot_data *data,
 	get_random_bytes(nonce, sizeof(nonce));
 	memcpy(&data->nonce_low, &nonce[0], sizeof(data->nonce_low));
 	memcpy(&data->nonce_high, &nonce[8], sizeof(data->nonce_high));
-	/* Build a random key */
-	get_random_bytes(aead_key, sizeof(aead_key));
-	rc = crypto_aead_setkey(data->aead_tfm, aead_key, sizeof(aead_key));
+
+	/* Create a kernel key, and set it. */
+	rc = snapshot_create_kernel_key(data);
+	if (rc)
+		goto fail;
+
+	payload = data->key->payload.data[0];
+	/* Install the key */
+	rc = crypto_aead_setkey(data->aead_tfm, payload->key, SNAPSHOT_ENCRYPTION_KEY_SIZE);
 	if (rc)
 		goto fail;
 
-	/* Hand the key back to user mode (to be changed!) */
-	rc = put_user(sizeof(struct uswsusp_key_blob), &key->blob_len);
+	/* Hand the key back to user mode in sealed form. */
+	rc = put_user(payload->blob_len, &key->blob_len);
 	if (rc)
 		goto fail;
 
-	rc = copy_to_user(&key->blob, &aead_key, sizeof(aead_key));
+	rc = copy_to_user(&key->blob, &payload->blob, payload->blob_len);
 	if (rc)
 		goto fail;
 
+	/* The nonce just gets handed back in the clear. */
 	rc = copy_to_user(&key->nonce, &nonce, sizeof(nonce));
 	if (rc)
 		goto fail;
@@ -426,10 +525,99 @@ int snapshot_get_encryption_key(struct snapshot_data *data,
 	return rc;
 }
 
+static int snapshot_load_kernel_key(struct snapshot_data *data,
+				    struct uswsusp_key_blob *blob)
+{
+
+	char *keytemplate = "load\t%s\tkeyhandle=0x81000000";
+	const struct cred *cred = current_cred();
+	struct tpm_digest *digests = NULL;
+	char *blobstring = NULL;
+	struct key *key = NULL;
+	struct tpm_chip *chip;
+	char *keyinfo = NULL;
+	int i, ret;
+
+	chip = tpm_default_chip();
+	if (!chip)
+		return -ENODEV;
+
+	if (!(tpm_is_tpm2(chip))) {
+		ret = -ENODEV;
+		goto out_dev;
+	}
+
+	ret = tpm2_pcr_reset(chip, 23);
+	if (ret)
+		goto out;
+
+	digests = kcalloc(chip->nr_allocated_banks, sizeof(struct tpm_digest),
+			  GFP_KERNEL);
+	if (!digests)
+		goto out;
+
+	for (i = 0; i < chip->nr_allocated_banks; i++) {
+		digests[i].alg_id = chip->allocated_banks[i].alg_id;
+		if (digests[i].alg_id == known_digest.alg_id)
+			memcpy(&digests[i], &known_digest, sizeof(known_digest));
+	}
+
+	ret = tpm_pcr_extend(chip, 23, digests);
+	if (ret != 0)
+		goto out;
+
+	blobstring = kmalloc(blob->blob_len * 2, GFP_KERNEL);
+	if (!blobstring) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	bin2hex(blobstring, blob->blob, blob->blob_len);
+	keyinfo = kasprintf(GFP_KERNEL, keytemplate, blobstring);
+	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);
+
+	if (IS_ERR(key)) {
+		ret = PTR_ERR(key);
+		key = NULL;
+		goto out;
+	}
+
+	ret = key_instantiate_and_link(key, keyinfo, strlen(keyinfo) + 1, NULL,
+				       NULL);
+	if (ret != 0)
+		goto out;
+
+	data->key = key;
+	key = NULL;
+
+out:
+	if (key) {
+		key_revoke(key);
+		key_put(key);
+	}
+
+	kfree(keyinfo);
+	kfree(blobstring);
+	kfree(digests);
+	tpm2_pcr_reset(chip, 23);
+
+out_dev:
+	put_device(&chip->dev);
+	return ret;
+}
+
 int snapshot_set_encryption_key(struct snapshot_data *data,
 				struct uswsusp_key_blob __user *key)
 {
 	struct uswsusp_key_blob blob;
+	struct trusted_key_payload *payload;
 	int rc;
 
 	/* It's too late if data's been pushed in. */
@@ -445,13 +633,18 @@ int snapshot_set_encryption_key(struct snapshot_data *data,
 	if (rc)
 		goto crypto_setup_fail;
 
-	if (blob.blob_len != sizeof(struct uswsusp_key_blob)) {
+	if (blob.blob_len > sizeof(key->blob)) {
 		rc = -EINVAL;
 		goto crypto_setup_fail;
 	}
 
+	rc = snapshot_load_kernel_key(data, &blob);
+	if (rc)
+		goto crypto_setup_fail;
+
+	payload = data->key->payload.data[0];
 	rc = crypto_aead_setkey(data->aead_tfm,
-				blob.blob,
+				payload->key,
 				SNAPSHOT_ENCRYPTION_KEY_SIZE);
 
 	if (rc)
diff --git a/kernel/power/user.h b/kernel/power/user.h
index ac429782abff85..6c86fb64ebe13e 100644
--- a/kernel/power/user.h
+++ b/kernel/power/user.h
@@ -31,6 +31,7 @@ struct snapshot_data {
 	uint64_t crypt_total;
 	uint64_t nonce_low;
 	uint64_t nonce_high;
+	struct key *key;
 #endif
 
 };
-- 
2.38.1.431.g37b22c650d-goog