Re: [PATCH] KEYS: trusted: Re-orchestrate tpm2_read_public() calls

Jarkko Sakkinen
2025-12-05T00:49:28Z

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On Fri, Dec 05, 2025 at 01:20:30AM +0200, Jarkko Sakkinen wrote:
> On Fri, Dec 05, 2025 at 12:31:27AM +0200, Jarkko Sakkinen wrote:
> > tpm2_load_cmd() and tpm2_unseal_cmd() use the same parent, and calls to
> > tpm_buf_append_name() cause the exact same TPM2_ReadPublic command to be
> > sent to the chip, causing unnecessary traffic.
> >
> > 1. Export tpm2_read_public in order to make it callable from 'trusted_tpm2'.
> > 2. Re-orchestrate tpm2_seal_trusted() and tpm2_unseal_trusted() in order to
> > halve the name resolutions required:
> > 2a. Move tpm2_read_public() calls into trusted_tpm2.
> > 2b. Pass TPM name to tpm_buf_append_name().
> > 2c. Rework tpm_buf_append_name() to use the pre-resolved name.
> >
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
>
> If ASN.1 blob would contain also name of the parent then zero
> tpm2_read_public() calls would be required i.e., the main bottleneck
> here inherits from the limitations of the file format itself.

Along the lines of attached patch.

BR, Jarkko

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From c5fc7e38aae838dd1190b33545a8b1a1696e9ce8 Mon Sep 17 00:00:00 2001
From: Jarkko Sakkinen <jarkko@kernel.org>
Date: Fri, 5 Dec 2025 01:53:33 +0200
Subject: [PATCH] KEYS: trusted: Extend TPMKey ASN.1 definition with
'parentName'

Extend TPMKey ASN.1 definition [1] with an optional 'parentName' attribute
containing TPMT_HA blob for the parent. Encode this attribute for the
generated TPM keys, which allows skipping TPM2_ReadPublic when unsealing
the key.

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

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
security/keys/trusted-keys/tpm2key.asn1 | 17 ++++-
security/keys/trusted-keys/trusted_tpm2.c | 80 +++++++++++++++--------
2 files changed, 69 insertions(+), 28 deletions(-)

diff --git a/security/keys/trusted-keys/tpm2key.asn1 b/security/keys/trusted-keys/tpm2key.asn1
index f57f869ad600..080f0e399982 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 [6] EXPLICIT OCTET STRING ({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 88bafbcc011a..85fd34457431 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 = 6,
+};
+
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, *end_name;
u16 priv_len, pub_len;
+ u8 *work, *work1;
+ u8 *priv, *pub;
int ret;

priv_len = get_unaligned_be16(src) + 2;
@@ -40,9 +50,13 @@ 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));

@@ -50,13 +64,22 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
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;
- }
- work = asn1_encode_tag(work, end_work, 0, bool, w - bool);
+ if (WARN(IS_ERR(w), "BUG: Boolean failed to encode"))
+ return PTR_ERR(w);
+ work = asn1_encode_tag(work, end_work, TPM_KEY_TAG_EMPTY_AUTH,
+ bool, w - bool);
}

+ u8 *name_encoded __free(kfree) = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
+ if (!name_encoded)
+ return -ENOMEM;
+
+ end_name = asn1_encode_octet_string(name_encoded,
+ name_encoded + SCRATCH_SIZE,
+ parent_name, parent_name_size);
+ work = asn1_encode_tag(work, end_work, TPM_KEY_TAG_PARENT_NAME,
+ name_encoded, end_name - name_encoded);
+
/*
* Assume both octet strings will encode to a 2 byte definite length
*
@@ -65,8 +88,7 @@ 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 +101,10 @@ 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 +113,13 @@ 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 +146,8 @@ 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 +211,16 @@ 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.
*
@@ -347,7 +378,8 @@ 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;

@@ -602,7 +634,7 @@ 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;
@@ -617,12 +649,6 @@ 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;
-
- parent_name_size = rc;
-
rc = tpm2_load_cmd(chip, payload, options, parent_name,
parent_name_size, blob, &blob_handle);
if (rc)
--
2.39.5