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Message-ID: <aTJN-TClJ0kNTu-v@kernel.org>
Date: Fri, 5 Dec 2025 05:14:01 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: linux-integrity@...r.kernel.org
Cc: Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Mimi Zohar <zohar@...ux.ibm.com>,
David Howells <dhowells@...hat.com>,
Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
open list <linux-kernel@...r.kernel.org>,
"open list:KEYS-TRUSTED" <keyrings@...r.kernel.org>,
"open list:SECURITY SUBSYSTEM" <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] KEYS: trusted: Store parent's name to the encoded
keys
On Fri, Dec 05, 2025 at 05:02:05AM +0200, Jarkko Sakkinen wrote:
> 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.
>
> [1] https://www.hansenpartnership.com/draft-bottomley-tpm2-keys.txt
>
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> ---
> v2:
> - A new patch.
> ---
> security/keys/trusted-keys/tpm2key.asn1 | 17 +++-
> security/keys/trusted-keys/trusted_tpm2.c | 97 ++++++++++++++++-------
> 2 files changed, 84 insertions(+), 30 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}),
Another nit. Should probably be instead:
parentName [6] 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 88bafbcc011a..3608dc9f7fa4 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, *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.
> *
> @@ -347,7 +383,8 @@ 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 +639,7 @@ 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;
> @@ -613,16 +650,18 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
> if (!options->keyhandle)
> return -EINVAL;
>
> + if (!parent_name_size) {
> + rc = tpm2_read_public(chip, options->keyhandle, parent_name);
> + if (rc < 0)
> + goto out;
> +
> + parent_name_size = rc;
> + }
> +
> rc = tpm_try_get_ops(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)
> --
> 2.52.0
>
BR, Jarkko
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