On Tue, Sep 27, 2022 at 09:49:19AM -0700, Evan Green wrote: > 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. > > Sourced-from: Matthew Garrett <mjg59@xxxxxxxxxx> > Signed-off-by: Evan Green <evgreen@xxxxxxxxxxxx> > > --- > Matthew's incarnation of this patch is at: > https://patchwork.kernel.org/project/linux-pm/patch/20210220013255.1083202-9-matthewgarrett@xxxxxxxxxx/ > > 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 | 1 + > kernel/power/snapenc.c | 207 +++++++++++++++++++++++++++++++++++++++-- > kernel/power/user.h | 1 + > 3 files changed, 200 insertions(+), 9 deletions(-) > > diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig > index cd574af0b43379..2f8acbd87b34dc 100644 > --- a/kernel/power/Kconfig > +++ b/kernel/power/Kconfig > @@ -96,6 +96,7 @@ config ENCRYPTED_HIBERNATION > bool "Encryption support for userspace snapshots" > depends on HIBERNATION_SNAPSHOT_DEV > depends on CRYPTO_AEAD2=y > + depends on TRUSTED_KEYS=y > default n > help > Enable support for kernel-based encryption of hibernation snapshots > diff --git a/kernel/power/snapenc.c b/kernel/power/snapenc.c > index cb90692d6ab83a..90079f6d4f184b 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 +323,12 @@ void snapshot_teardown_encryption(struct snapshot_data *data) > { > int i; > > + if (data->key) { Would be a helpful to have perhaps inline comment before the check. Just stating this because I did not exactly follow why the null check was needed (but do believe that there are good reasons to do it). > + 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; > @@ -381,11 +397,83 @@ static int snapshot_setup_encryption_common(struct snapshot_data *data) > return rc; > } > > +static int snapshot_create_kernel_key(struct snapshot_data *data) > +{ > + const struct cred *cred = current_cred(); > + struct tpm_digest *digests = NULL; > + struct tpm_chip *chip; > + struct key *key = NULL; > + int ret, i; > + /* Create a key sealed by the SRK. */ > + char *keyinfo = "new\t32\tkeyhandle=0x81000000"; Again, I'd consider put this declaration as first. > + > + chip = tpm_default_chip(); > + if (!chip) > + return -ENODEV; > + > + if (!(tpm_is_tpm2(chip))) { > + ret = -ENODEV; > + goto out_dev; > + } > + > + ret = tpm_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, strlen(keyinfo) + 1, NULL, > + NULL); Generally speaking, even if it somehow would be "safe", not strlen() thank you. AFAIK, keyinfo is a constant so you could just as well use sizeof(). And then you would not need "+ 1". > + if (ret != 0) > + goto out; > + > + data->key = key; > + key = NULL; > + > +out: > + if (key) { > + key_revoke(key); > + key_put(key); > + } > + > + kfree(digests); > + tpm_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]; > u8 nonce[USWSUSP_KEY_NONCE_SIZE]; > + struct trusted_key_payload *payload; > int rc; > /* Don't pull a random key from a world that can be reset. */ > if (data->ready) > @@ -399,21 +487,28 @@ 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; > @@ -425,10 +520,99 @@ 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) Bad alignment. > +{ > + > + const struct cred *cred = current_cred(); > + char *keytemplate = "load\t%s\tkeyhandle=0x81000000"; Ditto. > + struct tpm_digest *digests = NULL; > + char *blobstring = NULL; > + char *keyinfo = NULL; > + struct tpm_chip *chip; > + struct key *key = NULL; > + int i, ret; > + > + chip = tpm_default_chip(); > + if (!chip) > + return -ENODEV; > + > + if (!(tpm_is_tpm2(chip))) { > + ret = -ENODEV; > + goto out_dev; > + } > + > + ret = tpm_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); Ditto. > + 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); > + tpm_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. */ > @@ -444,13 +628,18 @@ 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 6823e2eba7ec53..591b30bb213349 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 > > }; > -- > 2.31.0 > BR, Jarkko
