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[PATCH v18 19/25] tpm2_key_protector: Support authorized policy
From: |
Gary Lin |
Subject: |
[PATCH v18 19/25] tpm2_key_protector: Support authorized policy |
Date: |
Fri, 28 Jun 2024 16:19:02 +0800 |
This commit handles the TPM2_PolicyAuthorize command from the key file
in TPM 2.0 Key File format.
TPM2_PolicyAuthorize is the essential command to support authorized
policy which allows the users to sign TPM policies with their own keys.
Per TPM 2.0 Key File(*1), CommandPolicy for TPM2_PolicyAuthorize
comprises 'TPM2B_PUBLIC pubkey', 'TPM2B_DIGEST policy_ref', and
'TPMT_SIGNATURE signature'. To verify the signature, the current policy
digest is hashed with the hash algorithm written in 'signature', and then
'signature' is verified with the hashed policy digest and 'pubkey'. Once
TPM accepts 'signature', TPM2_PolicyAuthorize is invoked to authorize the
signed policy.
To create the key file with authorized policy, here are the pcr-oracle(*2)
commands:
# Generate the RSA key and create the authorized policy file
$ pcr-oracle \
--rsa-generate-key \
--private-key policy-key.pem \
--auth authorized.policy \
create-authorized-policy 0,2,4,7,9
# Seal the secret with the authorized policy
$ pcr-oracle \
--key-format tpm2.0 \
--auth authorized.policy \
--input disk-secret.txt \
--output sealed.key \
seal-secret
# Sign the predicted PCR policy
$ pcr-oracle \
--key-format tpm2.0 \
--private-key policy-key.pem \
--from eventlog \
--stop-event "grub-file=grub.cfg" \
--after \
--input sealed.key \
--output sealed.tpm \
sign 0,2,4,7,9
Then specify the key file and the key protector to grub.cfg in the EFI
system partition:
tpm2_key_protector_init -a RSA --tpm2key=(hd0,gpt1)/boot/grub2/sealed.tpm
cryptomount -u <PART_UUID> -P tpm2
For any change in the boot components, just run the 'sign' command again
to update the signature in sealed.tpm, and TPM can unseal the key file
with the updated PCR policy.
(*1) https://www.hansenpartnership.com/draft-bottomley-tpm2-keys.html
(*2) https://github.com/okirch/pcr-oracle
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
---
.../commands/tpm2_key_protector/module.c | 72 +++++++++++++++++++
1 file changed, 72 insertions(+)
diff --git a/grub-core/commands/tpm2_key_protector/module.c
b/grub-core/commands/tpm2_key_protector/module.c
index 79440474b..a98109c43 100644
--- a/grub-core/commands/tpm2_key_protector/module.c
+++ b/grub-core/commands/tpm2_key_protector/module.c
@@ -618,6 +618,75 @@ grub_tpm2_protector_policypcr (TPMI_SH_AUTH_SESSION
session,
return GRUB_ERR_NONE;
}
+static grub_err_t
+grub_tpm2_protector_policyauthorize (TPMI_SH_AUTH_SESSION session,
+ struct grub_tpm2_buffer *cmd_buf)
+{
+ TPM2B_PUBLIC pubkey;
+ TPM2B_DIGEST policy_ref;
+ TPMT_SIGNATURE signature;
+ TPM2B_DIGEST pcr_policy;
+ TPM2B_DIGEST pcr_policy_hash;
+ TPMI_ALG_HASH sig_hash;
+ TPMT_TK_VERIFIED verification_ticket;
+ TPM_HANDLE pubkey_handle = 0;
+ TPM2B_NAME pubname;
+ TPM_RC rc;
+ grub_err_t err;
+
+ grub_Tss2_MU_TPM2B_PUBLIC_Unmarshal (cmd_buf, &pubkey);
+ grub_Tss2_MU_TPM2B_DIGEST_Unmarshal (cmd_buf, &policy_ref);
+ grub_Tss2_MU_TPMT_SIGNATURE_Unmarshal (cmd_buf, &signature);
+ if (cmd_buf->error != 0)
+ return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("Failed to unmarshal the
buffer for TPM2_PolicyAuthorize"));
+
+ /* Retrieve Policy Digest */
+ rc = TPM2_PolicyGetDigest (session, NULL, &pcr_policy, NULL);
+ if (rc != TPM_RC_SUCCESS)
+ return grub_error (GRUB_ERR_BAD_DEVICE, N_("Failed to get policy digest
(TPM2_PolicyGetDigest: 0x%x)."), rc);
+
+ /* Calculate the digest of the polcy for VerifySignature */
+ sig_hash = TPMT_SIGNATURE_get_hash_alg (&signature);
+ if (sig_hash == TPM_ALG_NULL)
+ return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("Failed to get the hash
algorithm of the signature"));
+
+ rc = TPM2_Hash (NULL, (TPM2B_MAX_BUFFER *)&pcr_policy, sig_hash,
+ TPM_RH_NULL, &pcr_policy_hash, NULL, NULL);
+ if (rc != TPM_RC_SUCCESS)
+ return grub_error (GRUB_ERR_BAD_DEVICE, N_("Failed to create PCR policy
hash (TPM2_Hash: 0x%x)"), rc);
+
+ /* Load the public key */
+ rc = TPM2_LoadExternal (NULL, NULL, &pubkey, TPM_RH_OWNER,
+ &pubkey_handle, &pubname, NULL);
+ if (rc != TPM_RC_SUCCESS)
+ return grub_error (GRUB_ERR_BAD_DEVICE, N_("Failed to load public key
(TPM2_LoadExternal: 0x%x)"), rc);
+
+ /* Verify the signature against the public key and the policy digest */
+ rc = TPM2_VerifySignature (pubkey_handle, NULL, &pcr_policy_hash, &signature,
+ &verification_ticket, NULL);
+ if (rc != TPM_RC_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_DEVICE, N_("Failed to verify signature
(TPM2_VerifySignature: 0x%x)"), rc);
+ goto error;
+ }
+
+ /* Authorize the signed policy with the public key and the verification
ticket */
+ rc = TPM2_PolicyAuthorize (session, NULL, &pcr_policy, &policy_ref, &pubname,
+ &verification_ticket, NULL);
+ if (rc != TPM_RC_SUCCESS)
+ {
+ err = grub_error (GRUB_ERR_BAD_DEVICE, N_("Failed to authorize PCR
policy (TPM2_PolicyAuthorize: 0x%x)"), rc);
+ goto error;
+ }
+
+ err = GRUB_ERR_NONE;
+
+ error:
+ TPM2_FlushContext (pubkey_handle);
+
+ return err;
+}
+
static grub_err_t
grub_tpm2_protector_enforce_policy (tpm2key_policy_t policy,
TPMI_SH_AUTH_SESSION session)
{
@@ -636,6 +705,9 @@ grub_tpm2_protector_enforce_policy (tpm2key_policy_t
policy, TPMI_SH_AUTH_SESSIO
case TPM_CC_PolicyPCR:
err = grub_tpm2_protector_policypcr (session, &buf);
break;
+ case TPM_CC_PolicyAuthorize:
+ err = grub_tpm2_protector_policyauthorize (session, &buf);
+ break;
default:
return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("Unknown TPM Command:
0x%x"), policy->cmd_code);
}
--
2.35.3
- [PATCH v18 11/25] libtasn1: Add the documentation, (continued)
- [PATCH v18 11/25] libtasn1: Add the documentation, Gary Lin, 2024/06/28
- [PATCH v18 12/25] key_protector: Add key protectors framework, Gary Lin, 2024/06/28
- [PATCH v18 13/25] tss2: Add TPM2 buffer handling functions, Gary Lin, 2024/06/28
- [PATCH v18 14/25] tss2: Add TPM2 types and Marshal/Unmarshal functions, Gary Lin, 2024/06/28
- [PATCH v18 15/25] tss2: Add TPM2 Software Stack (TSS2) support, Gary Lin, 2024/06/28
- [PATCH v18 16/25] key_protector: Add TPM2 Key Protector, Gary Lin, 2024/06/28
- [PATCH v18 17/25] cryptodisk: Support key protectors, Gary Lin, 2024/06/28
- [PATCH v18 18/25] util/grub-protect: Add new tool, Gary Lin, 2024/06/28
- [PATCH v18 19/25] tpm2_key_protector: Support authorized policy,
Gary Lin <=
- [PATCH v18 21/25] cryptodisk: Fallback to passphrase, Gary Lin, 2024/06/28
- [PATCH v18 20/25] tpm2_key_protector: Implement NV index, Gary Lin, 2024/06/28
- [PATCH v18 22/25] cryptodisk: wipe out the cached keys from protectors, Gary Lin, 2024/06/28
- [PATCH v18 25/25] tests: Add tpm2_key_protector_test, Gary Lin, 2024/06/28
- [PATCH v18 23/25] diskfilter: look up cryptodisk devices first, Gary Lin, 2024/06/28
- [PATCH v18 24/25] tpm2_key_protector: Add grub-emu support, Gary Lin, 2024/06/28