[RFC PATCH 1/1] KEYS, integrity: Link .platform keyring to .secondary_trusted_keys

[Kairui Song]

Currently kexec may need to verify the kerne image, and the kernel image
could be signed with third part keys which are provided by paltform or
firmware (eg. stored in MokListRT EFI variable). And the same time,
kexec_file_load will only verify the image agains .builtin_trusted_keys
or .secondary_trusted_keys according to configuration, but there is no
way for kexec_file_load to verify the image against any third part keys
mentioned above.

In ea93102f3224 ('integrity: Define a trusted platform keyring') a
.platform keyring is introduced to store the keys provided by platform
or firmware. And with a few following commits including 15ea0e1e3e185
('efi: Import certificates from UEFI Secure Boot'), now keys required to
verify the image is being imported to .paltform keyring, and later
IMA-appraisal could access the keyring and verify the image.

This patch links the .platform keyring to .secondary_trusted_keys so
kexec_file_load could also leverage the .platform keyring to verify the
kernel image.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxx>
---
 certs/system_keyring.c          | 30 ++++++++++++++++++++++++++++++
 include/keys/platform_keyring.h | 12 ++++++++++++
 security/integrity/digsig.c     |  7 +++++++
 3 files changed, 49 insertions(+)
 create mode 100644 include/keys/platform_keyring.h

diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 81728717523d..dcef0259e149 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -18,12 +18,14 @@
 #include <linux/verification.h>
 #include <keys/asymmetric-type.h>
 #include <keys/system_keyring.h>
+#include <keys/platform_keyring.h>
 #include <crypto/pkcs7.h>
 
 static struct key *builtin_trusted_keys;
 #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
 static struct key *secondary_trusted_keys;
 #endif
+static struct key *platform_keys = NULL;
 
 extern __initconst const u8 system_certificate_list[];
 extern __initconst const unsigned long system_certificate_list_size;
@@ -67,6 +69,12 @@ int restrict_link_by_builtin_and_secondary_trusted(
 		/* Allow the builtin keyring to be added to the secondary */
 		return 0;
 
+	if (type == &key_type_keyring &&
+	    dest_keyring == secondary_trusted_keys &&
+	    payload == &platform_keys->payload)
+		/* Allow the platform keyring to be added to the secondary */
+		return 0;
+
 	return restrict_link_by_signature(dest_keyring, type, payload,
 					  secondary_trusted_keys);
 }
@@ -188,6 +196,28 @@ static __init int load_system_certificate_list(void)
 }
 late_initcall(load_system_certificate_list);
 
+#if defined(CONFIG_INTEGRITY_PLATFORM_KEYRING) && defined(CONFIG_SECONDARY_TRUSTED_KEYRING)
+
+/*
+ * Link .platform keyring to .secondary_trusted_key keyring
+ */
+static __init int load_platform_certificate_list(void)
+{
+	int ret = 0;
+	platform_keys = integrity_get_platform_keyring();
+	if (!platform_keys) {
+		return 0;
+	}
+	ret = key_link(secondary_trusted_keys, platform_keys);
+	if (ret < 0) {
+		pr_err("Failed to link platform keyring: %d", ret);
+	}
+	return 0;
+}
+late_initcall(load_platform_certificate_list);
+
+#endif
+
 #ifdef CONFIG_SYSTEM_DATA_VERIFICATION
 
 /**
diff --git a/include/keys/platform_keyring.h b/include/keys/platform_keyring.h
new file mode 100644
index 000000000000..4f92ed6c0b42
--- /dev/null
+++ b/include/keys/platform_keyring.h
@@ -0,0 +1,12 @@
+#ifndef _KEYS_PLATFORM_KEYRING_H
+#define _KEYS_PLATFORM_KEYRING_H
+
+#include <linux/key.h>
+
+#ifdef CONFIG_INTEGRITY_PLATFORM_KEYRING
+
+extern const struct key* __init integrity_get_platform_keyring(void);
+
+#endif /* CONFIG_INTEGRITY_PLATFORM_KEYRING */
+
+#endif /* _KEYS_SYSTEM_KEYRING_H */
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index f45d6edecf99..397758d4f12d 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -176,3 +176,10 @@ int __init integrity_load_cert(const unsigned int id, const char *source,
 	pr_info("Loading X.509 certificate: %s\n", source);
 	return integrity_add_key(id, data, len, perm);
 }
+
+#ifdef CONFIG_INTEGRITY_PLATFORM_KEYRING
+struct key* __init integrity_get_platform_keyring(void)
+{
+	return keyring[INTEGRITY_KEYRING_PLATFORM];
+}
+#endif
-- 
2.20.1