In addition to the private key and public key, the TPM2_Create
command may also return creation data, a creation hash, and a creation
ticket. These fields allow the TPM to attest to the contents of a
specified set of PCRs at the time the trusted key was created. Encrypted
hibernation will use this to ensure that PCRs settable only by the
kernel were set properly at the time of creation, indicating this is an
authentic hibernate key.
Encode these additional parameters into the ASN.1 created to represent
the key blob. The new fields are made optional so that they don't bloat
key blobs which don't need them, and to ensure interoperability with
old blobs.
Signed-off-by: Evan Green <[email protected]>
---
(no changes since v3)
Changes in v3:
- Fix SoB and -- note ordering (Kees)
- Add comments describing the TPM2 spec type names for the new fields
in tpm2key.asn1 (Kees)
- Add len buffer checks in tpm2_key_encode() (Kees)
This is a replacement for Matthew's original patch here:
https://patchwork.kernel.org/patch/12096489/
That patch was written before the exported key format was switched to
ASN.1. This patch accomplishes the same thing (saving, loading, and
getting pointers to the creation data) while utilizing the new ASN.1
format.
---
include/keys/trusted-type.h | 8 +
security/keys/trusted-keys/tpm2key.asn1 | 15 +-
security/keys/trusted-keys/trusted_tpm2.c | 216 +++++++++++++++++++---
3 files changed, 213 insertions(+), 26 deletions(-)
diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
index 4eb64548a74f1a..209086fed240a5 100644
--- a/include/keys/trusted-type.h
+++ b/include/keys/trusted-type.h
@@ -22,15 +22,23 @@
#define MAX_BLOB_SIZE 512
#define MAX_PCRINFO_SIZE 64
#define MAX_DIGEST_SIZE 64
+#define MAX_CREATION_DATA 412
+#define MAX_TK 76
struct trusted_key_payload {
struct rcu_head rcu;
unsigned int key_len;
unsigned int blob_len;
+ unsigned int creation_len;
+ unsigned int creation_hash_len;
+ unsigned int tk_len;
unsigned char migratable;
unsigned char old_format;
unsigned char key[MAX_KEY_SIZE + 1];
unsigned char blob[MAX_BLOB_SIZE];
+ unsigned char *creation;
+ unsigned char *creation_hash;
+ unsigned char *tk;
};
struct trusted_key_options {
diff --git a/security/keys/trusted-keys/tpm2key.asn1 b/security/keys/trusted-keys/tpm2key.asn1
index f57f869ad60068..608f8d9ca95fa8 100644
--- a/security/keys/trusted-keys/tpm2key.asn1
+++ b/security/keys/trusted-keys/tpm2key.asn1
@@ -7,5 +7,18 @@ TPMKey ::= SEQUENCE {
emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL,
parent INTEGER ({tpm2_key_parent}),
pubkey OCTET STRING ({tpm2_key_pub}),
- privkey OCTET STRING ({tpm2_key_priv})
+ privkey OCTET STRING ({tpm2_key_priv}),
+ ---
+ --- A TPM2B_CREATION_DATA struct as returned from the TPM2_Create command.
+ ---
+ creationData [1] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_data}),
+ ---
+ --- A TPM2B_DIGEST of the creationHash as returned from the TPM2_Create
+ --- command.
+ ---
+ creationHash [2] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_hash}),
+ ---
+ --- A TPMT_TK_CREATION ticket as returned from the TPM2_Create command.
+ ---
+ creationTk [3] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_tk})
}
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 2b2c8eb258d5bd..e1388d7d799a36 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -33,19 +33,54 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
u8 *src, u32 len)
{
const int SCRATCH_SIZE = PAGE_SIZE;
+ u8 *end = src + len;
u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
u8 *work = scratch, *work1;
u8 *end_work = scratch + SCRATCH_SIZE;
u8 *priv, *pub;
+ u8 *creation_data = NULL, *creation_hash = NULL, *creation_tk = NULL;
+ u16 creation_data_len, creation_hash_len = 0, creation_tk_len = 0;
u16 priv_len, pub_len;
+ int rc;
+
+ if (src + 2 > end)
+ return -EINVAL;
priv_len = get_unaligned_be16(src) + 2;
priv = src;
src += priv_len;
-
+ if (src + 2 > end)
+ return -EINVAL;
pub_len = get_unaligned_be16(src) + 2;
pub = src;
+ src += pub_len;
+ if (src + 2 > end)
+ return -EINVAL;
+ creation_data_len = get_unaligned_be16(src);
+ if (creation_data_len) {
+ creation_data_len += 2;
+ creation_data = src;
+ src += creation_data_len;
+ if (src + 2 > end)
+ return -EINVAL;
+
+ creation_hash_len = get_unaligned_be16(src) + 2;
+ creation_hash = src;
+ src += creation_hash_len;
+ if (src + 2 > end)
+ return -EINVAL;
+
+ /*
+ * The creation ticket (TPMT_TK_CREATION) consists of a 2 byte
+ * tag, 4 byte handle, and then a TPM2B_DIGEST, which is a 2
+ * byte length followed by data.
+ */
+ creation_tk_len = get_unaligned_be16(src + 6) + 8;
+ creation_tk = src;
+ if (creation_tk + creation_tk_len > end)
+ return -EINVAL;
+ }
if (!scratch)
return -ENOMEM;
@@ -63,26 +98,81 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
}
/*
- * Assume both octet strings will encode to a 2 byte definite length
+ * Assume each octet string will encode to a 2 byte definite length.
+ * Each optional octet string consumes one extra byte.
*
- * Note: For a well behaved TPM, this warning should never
- * trigger, so if it does there's something nefarious going on
+ * Note: For a well behaved TPM, this warning should never trigger, so
+ * if it does there's something nefarious going on
*/
- if (WARN(work - scratch + pub_len + priv_len + 14 > SCRATCH_SIZE,
- "BUG: scratch buffer is too small"))
- return -EINVAL;
+ if (WARN(work - scratch + pub_len + priv_len + creation_data_len +
+ creation_hash_len + creation_tk_len + (7 * 5) + 3 >
+ SCRATCH_SIZE,
+ "BUG: scratch buffer is too small")) {
+ rc = -EINVAL;
+ goto err;
+ }
work = asn1_encode_integer(work, end_work, options->keyhandle);
work = asn1_encode_octet_string(work, end_work, pub, pub_len);
work = asn1_encode_octet_string(work, end_work, priv, priv_len);
+ if (creation_data_len) {
+ u8 *scratch2 = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
+ u8 *work2;
+ u8 *end_work2 = scratch2 + SCRATCH_SIZE;
+
+ if (!scratch2) {
+ rc = -ENOMEM;
+ goto err;
+ }
+
+ work2 = asn1_encode_octet_string(scratch2,
+ end_work2,
+ creation_data,
+ creation_data_len);
+
+ work = asn1_encode_tag(work,
+ end_work,
+ 1,
+ scratch2,
+ work2 - scratch2);
+
+ work2 = asn1_encode_octet_string(scratch2,
+ end_work2,
+ creation_hash,
+ creation_hash_len);
+
+ work = asn1_encode_tag(work,
+ end_work,
+ 2,
+ scratch2,
+ work2 - scratch2);
+
+ work2 = asn1_encode_octet_string(scratch2,
+ end_work2,
+ creation_tk,
+ creation_tk_len);
+
+ work = asn1_encode_tag(work,
+ end_work,
+ 3,
+ scratch2,
+ work2 - scratch2);
+
+ kfree(scratch2);
+ }
work1 = payload->blob;
work1 = asn1_encode_sequence(work1, work1 + sizeof(payload->blob),
scratch, work - scratch);
- if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed"))
- return PTR_ERR(work1);
+ if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed")) {
+ rc = PTR_ERR(work1);
+ goto err;
+ }
return work1 - payload->blob;
+err:
+ kfree(scratch);
+ return rc;
}
struct tpm2_key_context {
@@ -91,15 +181,21 @@ struct tpm2_key_context {
u32 pub_len;
const u8 *priv;
u32 priv_len;
+ const u8 *creation_data;
+ u32 creation_data_len;
+ const u8 *creation_hash;
+ u32 creation_hash_len;
+ const u8 *creation_tk;
+ u32 creation_tk_len;
};
static int tpm2_key_decode(struct trusted_key_payload *payload,
- struct trusted_key_options *options,
- u8 **buf)
+ struct trusted_key_options *options)
{
+ u64 data_len;
int ret;
struct tpm2_key_context ctx;
- u8 *blob;
+ u8 *blob, *buf;
memset(&ctx, 0, sizeof(ctx));
@@ -108,21 +204,57 @@ static int tpm2_key_decode(struct trusted_key_payload *payload,
if (ret < 0)
return ret;
- if (ctx.priv_len + ctx.pub_len > MAX_BLOB_SIZE)
+ data_len = ctx.priv_len + ctx.pub_len + ctx.creation_data_len +
+ ctx.creation_hash_len + ctx.creation_tk_len;
+
+ if (data_len > MAX_BLOB_SIZE)
return -EINVAL;
- blob = kmalloc(ctx.priv_len + ctx.pub_len + 4, GFP_KERNEL);
- if (!blob)
+ buf = kmalloc(data_len + 4, GFP_KERNEL);
+ if (!buf)
return -ENOMEM;
- *buf = blob;
+ blob = buf;
options->keyhandle = ctx.parent;
memcpy(blob, ctx.priv, ctx.priv_len);
blob += ctx.priv_len;
memcpy(blob, ctx.pub, ctx.pub_len);
+ blob += ctx.pub_len;
+ if (ctx.creation_data_len) {
+ memcpy(blob, ctx.creation_data, ctx.creation_data_len);
+ blob += ctx.creation_data_len;
+ }
+
+ if (ctx.creation_hash_len) {
+ memcpy(blob, ctx.creation_hash, ctx.creation_hash_len);
+ blob += ctx.creation_hash_len;
+ }
+
+ if (ctx.creation_tk_len) {
+ memcpy(blob, ctx.creation_tk, ctx.creation_tk_len);
+ blob += ctx.creation_tk_len;
+ }
+
+ /*
+ * Copy the buffer back into the payload blob since the creation
+ * info will be used after loading.
+ */
+ payload->blob_len = blob - buf;
+ memcpy(payload->blob, buf, payload->blob_len);
+ if (ctx.creation_data_len) {
+ payload->creation = payload->blob + ctx.priv_len + ctx.pub_len;
+ payload->creation_len = ctx.creation_data_len;
+ payload->creation_hash = payload->creation + ctx.creation_data_len;
+ payload->creation_hash_len = ctx.creation_hash_len;
+ payload->tk = payload->creation_hash +
+ payload->creation_hash_len;
+
+ payload->tk_len = ctx.creation_tk_len;
+ }
+ kfree(buf);
return 0;
}
@@ -185,6 +317,42 @@ int tpm2_key_priv(void *context, size_t hdrlen,
return 0;
}
+int tpm2_key_creation_data(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct tpm2_key_context *ctx = context;
+
+ ctx->creation_data = value;
+ ctx->creation_data_len = vlen;
+
+ return 0;
+}
+
+int tpm2_key_creation_hash(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct tpm2_key_context *ctx = context;
+
+ ctx->creation_hash = value;
+ ctx->creation_hash_len = vlen;
+
+ return 0;
+}
+
+int tpm2_key_creation_tk(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct tpm2_key_context *ctx = context;
+
+ ctx->creation_tk = value;
+ ctx->creation_tk_len = vlen;
+
+ return 0;
+}
+
/**
* tpm_buf_append_auth() - append TPMS_AUTH_COMMAND to the buffer.
*
@@ -229,6 +397,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
struct trusted_key_options *options)
{
int blob_len = 0;
+ unsigned int offset;
struct tpm_buf buf;
u32 hash;
u32 flags;
@@ -317,13 +486,14 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
rc = -E2BIG;
goto out;
}
- if (tpm_buf_length(&buf) < TPM_HEADER_SIZE + 4 + blob_len) {
+ offset = TPM_HEADER_SIZE + 4;
+ if (tpm_buf_length(&buf) < offset + blob_len) {
rc = -EFAULT;
goto out;
}
blob_len = tpm2_key_encode(payload, options,
- &buf.data[TPM_HEADER_SIZE + 4],
+ &buf.data[offset],
blob_len);
out:
@@ -370,13 +540,11 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
int rc;
u32 attrs;
- rc = tpm2_key_decode(payload, options, &blob);
- if (rc) {
- /* old form */
- blob = payload->blob;
+ rc = tpm2_key_decode(payload, options);
+ if (rc)
payload->old_format = 1;
- }
+ blob = payload->blob;
/* new format carries keyhandle but old format doesn't */
if (!options->keyhandle)
return -EINVAL;
@@ -433,8 +601,6 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
(__be32 *) &buf.data[TPM_HEADER_SIZE]);
out:
- if (blob != payload->blob)
- kfree(blob);
tpm_buf_destroy(&buf);
if (rc > 0)
--
2.38.1.431.g37b22c650d-goog
On Thu, Nov 03, 2022 at 11:01:12AM -0700, Evan Green wrote:
> In addition to the private key and public key, the TPM2_Create
> command may also return creation data, a creation hash, and a creation
> ticket. These fields allow the TPM to attest to the contents of a
> specified set of PCRs at the time the trusted key was created. Encrypted
> hibernation will use this to ensure that PCRs settable only by the
> kernel were set properly at the time of creation, indicating this is an
> authentic hibernate key.
>
> Encode these additional parameters into the ASN.1 created to represent
> the key blob. The new fields are made optional so that they don't bloat
> key blobs which don't need them, and to ensure interoperability with
> old blobs.
>
> Signed-off-by: Evan Green <[email protected]>
There's a lot of open-coded math for the bounds checking. I didn't
immediately see any problems, but it'd be nice if there was a way to
hook a fuzzer up to this, or at least write some KUnit tests to check
boundary conditions explicitly.
Reviewed-by: Kees Cook <[email protected]>
--
Kees Cook
On Fri, Nov 4, 2022 at 11:33 AM Kees Cook <[email protected]> wrote:
>
> On Thu, Nov 03, 2022 at 11:01:12AM -0700, Evan Green wrote:
> > In addition to the private key and public key, the TPM2_Create
> > command may also return creation data, a creation hash, and a creation
> > ticket. These fields allow the TPM to attest to the contents of a
> > specified set of PCRs at the time the trusted key was created. Encrypted
> > hibernation will use this to ensure that PCRs settable only by the
> > kernel were set properly at the time of creation, indicating this is an
> > authentic hibernate key.
> >
> > Encode these additional parameters into the ASN.1 created to represent
> > the key blob. The new fields are made optional so that they don't bloat
> > key blobs which don't need them, and to ensure interoperability with
> > old blobs.
> >
> > Signed-off-by: Evan Green <[email protected]>
>
> There's a lot of open-coded math for the bounds checking. I didn't
> immediately see any problems, but it'd be nice if there was a way to
> hook a fuzzer up to this, or at least write some KUnit tests to check
> boundary conditions explicitly.
>
> Reviewed-by: Kees Cook <[email protected]>
Thank you! Yes, agreed about all the bounds checking. I could probably
pull out the "check for src + 2 > end, then get_unaligned_be16()" into
a helper function. Let me see if that makes things look better or ends
up looking the same.
-Evan
On Mon, Nov 7, 2022 at 12:11 PM Evan Green <[email protected]> wrote:
>
> On Fri, Nov 4, 2022 at 11:33 AM Kees Cook <[email protected]> wrote:
> >
> > On Thu, Nov 03, 2022 at 11:01:12AM -0700, Evan Green wrote:
> > > In addition to the private key and public key, the TPM2_Create
> > > command may also return creation data, a creation hash, and a creation
> > > ticket. These fields allow the TPM to attest to the contents of a
> > > specified set of PCRs at the time the trusted key was created. Encrypted
> > > hibernation will use this to ensure that PCRs settable only by the
> > > kernel were set properly at the time of creation, indicating this is an
> > > authentic hibernate key.
> > >
> > > Encode these additional parameters into the ASN.1 created to represent
> > > the key blob. The new fields are made optional so that they don't bloat
> > > key blobs which don't need them, and to ensure interoperability with
> > > old blobs.
> > >
> > > Signed-off-by: Evan Green <[email protected]>
> >
> > There's a lot of open-coded math for the bounds checking. I didn't
> > immediately see any problems, but it'd be nice if there was a way to
> > hook a fuzzer up to this, or at least write some KUnit tests to check
> > boundary conditions explicitly.
> >
> > Reviewed-by: Kees Cook <[email protected]>
>
> Thank you! Yes, agreed about all the bounds checking. I could probably
> pull out the "check for src + 2 > end, then get_unaligned_be16()" into
> a helper function. Let me see if that makes things look better or ends
> up looking the same.
A helper function cleaned this up nicely, so I'll send that in the
next spin but not yet pick up your reviewed tag.