grub2/0004-tpm2-Support-authorized-policy.patch

From d6e2d32d53d9a1aac2383fc6c075f3827111b643 Mon Sep 17 00:00:00 2001
From: Gary Lin <glin@suse.com>
Date: Thu, 6 Apr 2023 16:00:25 +0800
Subject: [PATCH 4/4] tpm2: Support authorized policy

TPM2_PolicyAuthorize is the key command to support authorized policy
which allows the users to sign TPM policies with their own keys.

Per TPM 2.0 Key File(*), CommandPolicy for TPM2_PolicyAuthorize
comprises 'TPM2B_PUBLIC pubkey', 'TPM2B_DIGEST policy_ref', and
'TPMT_SIGNATURE signature'. This commit unmarshals those data
structures, fetches the current policy digest, hashes the policy digest
with the hash algorithm written in 'signature', and then verifies
'signature' with 'pubkey'. If everything goes well, TPM2_PolicyAuthorize
is invoked to authorize the signed policy.

(*) https://www.hansenpartnership.com/draft-bottomley-tpm2-keys.html

Signed-off-by: Gary Lin <glin@suse.com>
---
 grub-core/tpm2/module.c | 98 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)

diff --git a/grub-core/tpm2/module.c b/grub-core/tpm2/module.c
index 5274296b7..e5235c2ac 100644
--- a/grub-core/tpm2/module.c
+++ b/grub-core/tpm2/module.c
@@ -454,6 +454,101 @@ 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_tpm2_mu_TPM2B_PUBLIC_Unmarshal (cmd_buf, &pubkey);
+  grub_tpm2_mu_TPM2B_DIGEST_Unmarshal (cmd_buf, &policy_ref);
+  grub_tpm2_mu_TPMT_SIGNATURE_Unmarshal (cmd_buf, &signature);
+  if (cmd_buf->error != 0)
+    {
+      err = GRUB_ERR_BAD_ARGUMENT;
+      return grub_error (err, 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)
+    {
+      err = GRUB_ERR_BAD_DEVICE;
+      grub_error (err, N_("Failed to get policy digest (TPM error: 0x%x)."),
+		  rc);
+      return err;
+    }
+
+  /* Calculate the digest of the polcy for VerifySignature */
+  sig_hash = TPMT_SIGNATURE_get_hash_alg (&signature);
+  if (sig_hash == TPM_ALG_NULL)
+    {
+      err = GRUB_ERR_BAD_ARGUMENT;
+      grub_error (err, N_("Failed to get the hash algorithm of the signature"));
+      return err;
+    }
+  rc = TPM2_Hash (NULL, (TPM2B_MAX_BUFFER *)&pcr_policy, sig_hash,
+		  TPM_RH_NULL, &pcr_policy_hash, NULL, NULL);
+  if (rc != TPM_RC_SUCCESS)
+    {
+      err = GRUB_ERR_BAD_DEVICE;
+      grub_error (err, N_("Failed to create PCR policy hash (TPM2_Hash failed "
+			  "with TSS/TPM error %u)"), rc);
+      return err;
+    }
+
+  /* Load the public key */
+  rc = TPM2_LoadExternal (NULL, NULL, &pubkey, TPM_RH_OWNER,
+			  &pubkey_handle, &pubname, NULL);
+  if (rc != TPM_RC_SUCCESS)
+    {
+      err = GRUB_ERR_BAD_DEVICE;
+      grub_error (err, N_("Failed to load public key (TPM2_LoadExternal failed "
+			  "with TSS/TPM error %u)"), rc);
+      return err;
+    }
+
+  /* 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_ERR_BAD_DEVICE;
+      grub_error (err, N_("Failed to verify signature (TPM2_VerifySignature "
+			  "failed with TSS/TPM error %u)"), 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_ERR_BAD_DEVICE;
+      grub_error (err, N_("Failed to authorize PCR policy (TPM2_PolicyAuthorize "
+			  "failed with TSS/TPM error: 0x%u).\n"), 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)
 {
@@ -473,6 +568,9 @@ 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