ipe: allow secondary and platform keyrings to install/update policies

The current policy management makes it impossible to use IPE
in a general purpose distribution. In such cases the users are not
building the kernel, the distribution is, and access to the private
key included in the trusted keyring is, for obvious reason, not
available.
This means that users have no way to enable IPE, since there will
be no built-in generic policy, and no access to the key to sign
updates validated by the trusted keyring.

Just as we do for dm-verity, kernel modules and more, allow the
secondary and platform keyrings to also validate policies. This
allows users enrolling their own keys in UEFI db or MOK to also
sign policies, and enroll them. This makes it sensible to enable
IPE in general purpose distributions, as it becomes usable by
any user wishing to do so. Keys in these keyrings can already
load kernels and kernel modules, so there is no security
downgrade.

Add a kconfig each, like dm-verity does, but default to enabled if
the dependencies are available.

Signed-off-by: Luca Boccassi <bluca@debian.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
[FW: fixed some style issues]
Signed-off-by: Fan Wu <wufan@kernel.org>

Documentation/admin-guide/LSM/ipe.rst

@@ -223,7 +223,10 @@ are signed through the PKCS#7 message format to enforce some level of
 authorization of the policies (prohibiting an attacker from gaining
 unconstrained root, and deploying an "allow all" policy). These
 policies must be signed by a certificate that chains to the
-``SYSTEM_TRUSTED_KEYRING``. With openssl, the policy can be signed by::
+``SYSTEM_TRUSTED_KEYRING``, or to the secondary and/or platform keyrings if
+``CONFIG_IPE_POLICY_SIG_SECONDARY_KEYRING`` and/or
+``CONFIG_IPE_POLICY_SIG_PLATFORM_KEYRING`` are enabled, respectively.
+With openssl, the policy can be signed by::
 
    openssl smime -sign \
       -in "$MY_POLICY" \

security/ipe/Kconfig

@@ -31,6 +31,25 @@ config IPE_BOOT_POLICY
 
 	  If unsure, leave blank.
 
+config IPE_POLICY_SIG_SECONDARY_KEYRING
+	bool "IPE policy update verification with secondary keyring"
+	default y
+	depends on SECONDARY_TRUSTED_KEYRING
+	help
+	  Also allow the secondary trusted keyring to verify IPE policy
+	  updates.
+
+	  If unsure, answer Y.
+
+config IPE_POLICY_SIG_PLATFORM_KEYRING
+	bool "IPE policy update verification with platform keyring"
+	default y
+	depends on INTEGRITY_PLATFORM_KEYRING
+	help
+	  Also allow the platform keyring to verify IPE policy updates.
+
+	  If unsure, answer Y.
+
 menu "IPE Trust Providers"
 
 config IPE_PROP_DM_VERITY

security/ipe/policy.c

@@ -169,9 +169,21 @@ struct ipe_policy *ipe_new_policy(const char *text, size_t textlen,
 			goto err;
 		}
 
-		rc = verify_pkcs7_signature(NULL, 0, new->pkcs7, pkcs7len, NULL,
+		rc = verify_pkcs7_signature(NULL, 0, new->pkcs7, pkcs7len,
+#ifdef CONFIG_IPE_POLICY_SIG_SECONDARY_KEYRING
+					    VERIFY_USE_SECONDARY_KEYRING,
+#else
+					    NULL,
+#endif
 					    VERIFYING_UNSPECIFIED_SIGNATURE,
 					    set_pkcs7_data, new);
+#ifdef CONFIG_IPE_POLICY_SIG_PLATFORM_KEYRING
+		if (rc == -ENOKEY)
+			rc = verify_pkcs7_signature(NULL, 0, new->pkcs7, pkcs7len,
+						    VERIFY_USE_PLATFORM_KEYRING,
+						    VERIFYING_UNSPECIFIED_SIGNATURE,
+						    set_pkcs7_data, new);
+#endif
 		if (rc)
 			goto err;
 	} else {