[PATCH v6 2/2] KEYS: trusted: Store parent's name to the encoded keys

Jarkko Sakkinen
2025-12-07T17:32:30Z

Extend TPMKey ASN.1 speciication [1] with an optional 'parentName'
attribute containing TPM name of the parent key (in other words, TPMT_HA
blob).

The life-cycle for trusted keys will now proceed as follows:

1. Encode parent's name to the 'paretName' during tpm2_key_encode().
2. During tpm2_unseal_trusted, read parent's name from 'parentName'. When
the attribute is not available, fallback on doing tpm2_read_public().

In other words, in the common (i.e., not loading a legacy key blob),
tpm2_read_public() will now only happen at the time when a key is first
created.

In addition, move tpm2_read_public() to 'tpm2-cmd.c' and make its body
unconditional so that the binary format of the saved keys is not dependent
on kernel configuration.

[1] https://www.hansenpartnership.com/draft-bottomley-tpm2-keys.txt

Cc: tpm2@lists.linux.dev
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
v6:
- Addressed the issues reported by James.

Updated tag index to '7', as '6' is reserved by "creation data proposal"
to which I could not find a reference but presumably exists:

https://lore.kernel.org/linux-integrity/89d90617ba9b7a5eff1d5fad6bb9773033d3c18c.camel@HansenPartnership.com/#t

Once I become aware of the mailing list of IETF WG for TPM2 ASN.1 key
spec, so could not cc to patch over there buth at least the conflict has
been addressed. I can add the list ass CC one I know th address.
v5:
- Rebased to the mainline.
v4:
- No changes.
v3:
- Fixed three low-hanging fruit issues I found myself.
v2:
- A new patch.
---
drivers/char/tpm/tpm2-cmd.c | 83 ++++++++++++++++++++
drivers/char/tpm/tpm2-sessions.c | 85 ---------------------
include/linux/tpm.h | 9 +--
security/keys/trusted-keys/tpm2key.asn1 | 17 ++++-
security/keys/trusted-keys/trusted_tpm2.c | 93 ++++++++++++++++-------
5 files changed, 166 insertions(+), 121 deletions(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 5b04e74b6377..83a70680cfe9 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -757,3 +757,86 @@ int tpm2_find_cc(struct tpm_chip *chip, u32 cc)

return -1;
}
+
+/*
+ * Name Size based on TPM algorithm (assumes no hash bigger than 255)
+ */
+static int name_size(const u8 *name)
+{
+ u16 hash_alg = get_unaligned_be16(name);
+
+ switch (hash_alg) {
+ case TPM_ALG_SHA1:
+ return SHA1_DIGEST_SIZE + 2;
+ case TPM_ALG_SHA256:
+ return SHA256_DIGEST_SIZE + 2;
+ case TPM_ALG_SHA384:
+ return SHA384_DIGEST_SIZE + 2;
+ case TPM_ALG_SHA512:
+ return SHA512_DIGEST_SIZE + 2;
+ default:
+ pr_warn("tpm: unsupported name algorithm: 0x%04x\n", hash_alg);
+ return -EINVAL;
+ }
+}
+
+/**
+ * tpm2_read_public: Resolve TPM name for a handle
+ * @chip: TPM chip to use.
+ * @handle: TPM handle.
+ * @name: A buffer for returning the name blob. Must have a
+ * capacity of 'SHA512_DIGET_SIZE + 2' bytes at minimum
+ *
+ * Returns size of TPM handle name of success.
+ * Returns tpm_transmit_cmd error codes when TPM2_ReadPublic fails.
+ */
+int tpm2_read_public(struct tpm_chip *chip, u32 handle, void *name)
+{
+ u32 mso = tpm2_handle_mso(handle);
+ off_t offset = TPM_HEADER_SIZE;
+ int rc, name_size_alg;
+
+ if (mso != TPM2_MSO_PERSISTENT && mso != TPM2_MSO_VOLATILE &&
+ mso != TPM2_MSO_NVRAM) {
+ memcpy(name, &handle, sizeof(u32));
+ return sizeof(u32);
+ }
+
+ struct tpm_buf *buf __free(kfree) = kzalloc(TPM_BUFSIZE, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ tpm_buf_init(buf, TPM_BUFSIZE);
+ tpm_buf_reset(buf, TPM2_ST_NO_SESSIONS, TPM2_CC_READ_PUBLIC);
+ tpm_buf_append_u32(buf, handle);
+
+ rc = tpm_transmit_cmd(chip, buf, 0, "TPM2_ReadPublic");
+ if (rc)
+ return tpm_ret_to_err(rc);
+
+ /* Skip TPMT_PUBLIC: */
+ offset += tpm_buf_read_u16(buf, &offset);
+
+ /*
+ * Ensure space for the length field of TPM2B_NAME and hashAlg field of
+ * TPMT_HA (the extra four bytes).
+ */
+ if (offset + 4 > tpm_buf_length(buf))
+ return -EIO;
+
+ rc = tpm_buf_read_u16(buf, &offset);
+ name_size_alg = name_size(&buf->data[offset]);
+
+ if (name_size_alg < 0)
+ return name_size_alg;
+
+ if (rc != name_size_alg)
+ return -EIO;
+
+ if (offset + rc > tpm_buf_length(buf))
+ return -EIO;
+
+ memcpy(name, &buf->data[offset], rc);
+ return name_size_alg;
+}
+EXPORT_SYMBOL_GPL(tpm2_read_public);
diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 6b7112a7c30c..daf78c2e905f 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -140,91 +140,6 @@ struct tpm2_auth {
u16 name_size_tbl[AUTH_MAX_NAMES];
};

-#ifdef CONFIG_TCG_TPM2_HMAC
-/*
- * Name Size based on TPM algorithm (assumes no hash bigger than 255)
- */
-static int name_size(const u8 *name)
-{
- u16 hash_alg = get_unaligned_be16(name);
-
- switch (hash_alg) {
- case TPM_ALG_SHA1:
- return SHA1_DIGEST_SIZE + 2;
- case TPM_ALG_SHA256:
- return SHA256_DIGEST_SIZE + 2;
- case TPM_ALG_SHA384:
- return SHA384_DIGEST_SIZE + 2;
- case TPM_ALG_SHA512:
- return SHA512_DIGEST_SIZE + 2;
- default:
- pr_warn("tpm: unsupported name algorithm: 0x%04x\n", hash_alg);
- return -EINVAL;
- }
-}
-
-/**
- * tpm2_read_public: Resolve TPM name for a handle
- * @chip: TPM chip to use.
- * @handle: TPM handle.
- * @name: A buffer for returning the name blob. Must have a
- * capacity of 'SHA512_DIGET_SIZE + 2' bytes at minimum
- *
- * Returns size of TPM handle name of success.
- * Returns tpm_transmit_cmd error codes when TPM2_ReadPublic fails.
- */
-int tpm2_read_public(struct tpm_chip *chip, u32 handle, void *name)
-{
- u32 mso = tpm2_handle_mso(handle);
- off_t offset = TPM_HEADER_SIZE;
- int rc, name_size_alg;
-
- if (mso != TPM2_MSO_PERSISTENT && mso != TPM2_MSO_VOLATILE &&
- mso != TPM2_MSO_NVRAM) {
- memcpy(name, &handle, sizeof(u32));
- return sizeof(u32);
- }
-
- struct tpm_buf *buf __free(kfree) = kzalloc(TPM_BUFSIZE, GFP_KERNEL);
- if (!buf)
- return -ENOMEM;
-
- tpm_buf_init(buf, TPM_BUFSIZE);
- tpm_buf_reset(buf, TPM2_ST_NO_SESSIONS, TPM2_CC_READ_PUBLIC);
- tpm_buf_append_u32(buf, handle);
-
- rc = tpm_transmit_cmd(chip, buf, 0, "TPM2_ReadPublic");
- if (rc)
- return tpm_ret_to_err(rc);
-
- /* Skip TPMT_PUBLIC: */
- offset += tpm_buf_read_u16(buf, &offset);
-
- /*
- * Ensure space for the length field of TPM2B_NAME and hashAlg field of
- * TPMT_HA (the extra four bytes).
- */
- if (offset + 4 > tpm_buf_length(buf))
- return -EIO;
-
- rc = tpm_buf_read_u16(buf, &offset);
- name_size_alg = name_size(&buf->data[offset]);
-
- if (name_size_alg < 0)
- return name_size_alg;
-
- if (rc != name_size_alg)
- return -EIO;
-
- if (offset + rc > tpm_buf_length(buf))
- return -EIO;
-
- memcpy(name, &buf->data[offset], rc);
- return name_size_alg;
-}
-EXPORT_SYMBOL_GPL(tpm2_read_public);
-#endif /* CONFIG_TCG_TPM2_HMAC */
-
/**
* tpm_buf_append_name() - Append a handle and store TPM name
* @chip: TPM chip to use.
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 3f1d8c27394b..40d1ede005b0 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -478,6 +478,7 @@ extern int tpm_get_random(struct tpm_chip *chip, u8 *data, size_t max);
extern struct tpm_chip *tpm_default_chip(void);
void tpm2_flush_context(struct tpm_chip *chip, u32 handle);
int tpm2_find_hash_alg(unsigned int crypto_id);
+int tpm2_read_public(struct tpm_chip *chip, u32 handle, void *name);

static inline void tpm_buf_append_empty_auth(struct tpm_buf *buf, u32 handle)
{
@@ -544,7 +545,6 @@ int tpm_buf_fill_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf);
int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
int rc);
void tpm2_end_auth_session(struct tpm_chip *chip);
-int tpm2_read_public(struct tpm_chip *chip, u32 handle, void *name);
#else
#include <linux/unaligned.h>

@@ -568,13 +568,6 @@ static inline int tpm_buf_check_hmac_response(struct tpm_chip *chip,
{
return rc;
}
-
-static inline int tpm2_read_public(struct tpm_chip *chip, u32 handle,
- void *name)
-{
- memcpy(name, &handle, sizeof(u32));
- return sizeof(u32);
-}
#endif /* CONFIG_TCG_TPM2_HMAC */

#endif
diff --git a/security/keys/trusted-keys/tpm2key.asn1 b/security/keys/trusted-keys/tpm2key.asn1
index f57f869ad600..c48ea5a14219 100644
--- a/security/keys/trusted-keys/tpm2key.asn1
+++ b/security/keys/trusted-keys/tpm2key.asn1
@@ -1,11 +1,26 @@
---
--- ASN.1 for TPM 2.0 keys
---
+TPMPolicy ::= SEQUENCE {
+ commandCode [0] EXPLICIT INTEGER,
+ commandPolicy [1] EXPLICIT OCTET STRING
+}
+
+TPMAuthPolicy ::= SEQUENCE {
+ name [0] EXPLICIT UTF8String OPTIONAL,
+ policy [1] EXPLICIT SEQUENCE OF TPMPolicy
+}

TPMKey ::= SEQUENCE {
type OBJECT IDENTIFIER ({tpm2_key_type}),
emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL,
+ policy [1] EXPLICIT SEQUENCE OF TPMPolicy OPTIONAL,
+ secret [2] EXPLICIT OCTET STRING OPTIONAL,
+ authPolicy [3] EXPLICIT SEQUENCE OF TPMAuthPolicy OPTIONAL,
+ description [4] EXPLICIT UTF8String OPTIONAL,
+ rsaParent [5] EXPLICIT BOOLEAN OPTIONAL,
+ parentName [7] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_parent_name}),
parent INTEGER ({tpm2_key_parent}),
pubkey OCTET STRING ({tpm2_key_pub}),
privkey OCTET STRING ({tpm2_key_priv})
- }
+}
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 0feb96cab62d..6ceb8cff3830 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -20,16 +20,26 @@

static u32 tpm2key_oid[] = { 2, 23, 133, 10, 1, 5 };

+enum tpm_key_tag {
+ TPM_KEY_TAG_EMPTY_AUTH = 0,
+ TPM_KEY_TAG_POLICY = 1,
+ TPM_KEY_TAG_SECRET = 2,
+ TPM_KEY_TAG_AUTH_POLICY = 3,
+ TPM_KEY_TAG_DESCRIPTION = 4,
+ TPM_KEY_TAG_RSA_PARENT = 5,
+ TPM_KEY_TAG_PARENT_NAME = 7,
+};
+
static int tpm2_key_encode(struct trusted_key_payload *payload,
struct trusted_key_options *options,
- u8 *src, u32 len)
+ u8 *src, u32 len, u8 *parent_name,
+ u16 parent_name_size)
{
const int SCRATCH_SIZE = PAGE_SIZE;
- u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
- u8 *work = scratch, *work1;
- u8 *end_work = scratch + SCRATCH_SIZE;
- u8 *priv, *pub;
+ u8 *end_work, *name_end;
u16 priv_len, pub_len;
+ u8 *work, *work1;
+ u8 *priv, *pub;
int ret;

priv_len = get_unaligned_be16(src) + 2;
@@ -40,23 +50,41 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
pub_len = get_unaligned_be16(src) + 2;
pub = src;

+ u8 *scratch __free(kfree) = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
if (!scratch)
return -ENOMEM;

+ work = scratch;
+ end_work = scratch + SCRATCH_SIZE;
+
work = asn1_encode_oid(work, end_work, tpm2key_oid,
asn1_oid_len(tpm2key_oid));

if (options->blobauth_len == 0) {
- unsigned char bool[3], *w = bool;
- /* tag 0 is emptyAuth */
- w = asn1_encode_boolean(w, w + sizeof(bool), true);
- if (WARN(IS_ERR(w), "BUG: Boolean failed to encode")) {
- ret = PTR_ERR(w);
- goto err;
+ u8 *bool_end;
+ u8 bool[3];
+
+ bool_end = asn1_encode_boolean(&bool[0], &bool[sizeof(bool)],
+ true);
+ if (IS_ERR(bool_end)) {
+ pr_err("BUG: Boolean failed to encode\n");
+ return PTR_ERR(bool_end);
}
- work = asn1_encode_tag(work, end_work, 0, bool, w - bool);
+
+ work = asn1_encode_tag(work, end_work, TPM_KEY_TAG_EMPTY_AUTH,
+ bool, bool_end - bool);
}

+ u8 *name_encoded __free(kfree) = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
+ if (!name_encoded)
+ return -ENOMEM;
+
+ name_end = asn1_encode_octet_string(&name_encoded[0],
+ &name_encoded[SCRATCH_SIZE],
+ parent_name, parent_name_size);
+ work = asn1_encode_tag(work, end_work, TPM_KEY_TAG_PARENT_NAME,
+ name_encoded, name_end - name_encoded);
+
/*
* Assume both octet strings will encode to a 2 byte definite length
*
@@ -65,8 +93,7 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
*/
if (WARN(work - scratch + pub_len + priv_len + 14 > SCRATCH_SIZE,
"BUG: scratch buffer is too small")) {
- ret = -EINVAL;
- goto err;
+ return -EINVAL;
}

work = asn1_encode_integer(work, end_work, options->keyhandle);
@@ -79,15 +106,10 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
if (IS_ERR(work1)) {
ret = PTR_ERR(work1);
pr_err("BUG: ASN.1 encoder failed with %d\n", ret);
- goto err;
+ return ret;
}

- kfree(scratch);
return work1 - payload->blob;
-
-err:
- kfree(scratch);
- return ret;
}

struct tpm2_key_context {
@@ -96,11 +118,13 @@ struct tpm2_key_context {
u32 pub_len;
const u8 *priv;
u32 priv_len;
+ const u8 *name;
+ u32 name_len;
};

static int tpm2_key_decode(struct trusted_key_payload *payload,
struct trusted_key_options *options,
- u8 **buf)
+ u8 **buf, u8 *parent_name, u16 *parent_name_size)
{
int ret;
struct tpm2_key_context ctx;
@@ -127,6 +151,8 @@ static int tpm2_key_decode(struct trusted_key_payload *payload,
blob += ctx.priv_len;

memcpy(blob, ctx.pub, ctx.pub_len);
+ memcpy(parent_name, ctx.name, ctx.name_len);
+ *parent_name_size = ctx.name_len;

return 0;
}
@@ -190,6 +216,16 @@ int tpm2_key_priv(void *context, size_t hdrlen,
return 0;
}

+int tpm2_key_parent_name(void *context, size_t hdrlen, unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct tpm2_key_context *ctx = context;
+
+ ctx->name = value;
+ ctx->name_len = vlen;
+
+ return 0;
+}
/**
* tpm2_buf_append_auth() - append TPMS_AUTH_COMMAND to the buffer.
*
@@ -351,7 +387,8 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
goto out;
}

- blob_len = tpm2_key_encode(payload, options, &buf->data[offset], blob_len);
+ blob_len = tpm2_key_encode(payload, options, &buf->data[offset],
+ blob_len, parent_name, parent_name_size);
if (blob_len < 0)
rc = blob_len;

@@ -596,7 +633,7 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
* Try to decode the provided blob as an ASN.1 blob. Assume that the
* blob is in the legacy format if decoding does not end successfully.
*/
- rc = tpm2_key_decode(payload, options, &blob);
+ rc = tpm2_key_decode(payload, options, &blob, &parent_name[0], &parent_name_size);
if (rc) {
blob = payload->blob;
payload->old_format = 1;
@@ -611,11 +648,13 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
if (rc)
return rc;

- rc = tpm2_read_public(chip, options->keyhandle, parent_name);
- if (rc < 0)
- goto out;
+ if (!parent_name_size) {
+ rc = tpm2_read_public(chip, options->keyhandle, parent_name);
+ if (rc < 0)
+ goto out;

- parent_name_size = rc;
+ parent_name_size = rc;
+ }

rc = tpm2_load_cmd(chip, payload, options, parent_name,
parent_name_size, blob, &blob_handle);
--
2.39.5