[PATCH v4 01/12] integrity: Introduce a Linux keyring for the Machine Owner Key (MOK)

Eric Snowberg
2021-08-19T00:22:20Z

Many UEFI Linux distributions boot using shim. The UEFI shim provides
what is called Machine Owner Keys (MOK). Shim uses both the UEFI Secure
Boot DB and MOK keys to validate the next step in the boot chain. The
MOK facility can be used to import user generated keys. These keys can
be used to sign an end-users development kernel build. When Linux
boots, both UEFI Secure Boot DB and MOK keys get loaded in the Linux
.platform keyring.

Add a new Linux keyring called .mok. This keyring shall contain just
MOK CA keys and not the remaining keys in the platform keyring. This new
.mok keyring will be used in follow on patches. Unlike keys in the
platform keyring, keys contained in the .mok keyring will be trusted
within the kernel if the end-user has chosen to do so.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
v1: Initial version
v2: Removed destory keyring code
v3: Unmodified from v2
v4: Add Kconfig, merged in "integrity: add add_to_mok_keyring"
---
security/integrity/Kconfig | 11 +++++
security/integrity/Makefile | 1 +
security/integrity/digsig.c | 1 +
security/integrity/integrity.h | 12 +++++-
.../integrity/platform_certs/mok_keyring.c | 42 +++++++++++++++++++
5 files changed, 66 insertions(+), 1 deletion(-)
create mode 100644 security/integrity/platform_certs/mok_keyring.c

diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
index 71f0177e8716..7a69021e2d42 100644
--- a/security/integrity/Kconfig
+++ b/security/integrity/Kconfig
@@ -62,6 +62,17 @@ config INTEGRITY_PLATFORM_KEYRING
provided by the platform for verifying the kexec'ed kerned image
and, possibly, the initramfs signature.

+config INTEGRITY_MOK_KEYRING
+ bool "Provide a keyring to which CA Machine Owner Keys may be added"
+ depends on SECONDARY_TRUSTED_KEYRING
+ depends on INTEGRITY_ASYMMETRIC_KEYS
+ depends on SYSTEM_BLACKLIST_KEYRING
+ help
+ If set, provide a keyring to which CA Machine Owner Keys (MOK) may
+ be added. This keyring shall contain just CA MOK keys. Unlike keys
+ in the platform keyring, keys contained in the .mok keyring will be
+ trusted within the kernel.
+
config LOAD_UEFI_KEYS
depends on INTEGRITY_PLATFORM_KEYRING
depends on EFI
diff --git a/security/integrity/Makefile b/security/integrity/Makefile
index 7ee39d66cf16..e3f4588a069c 100644
--- a/security/integrity/Makefile
+++ b/security/integrity/Makefile
@@ -10,6 +10,7 @@ integrity-$(CONFIG_INTEGRITY_AUDIT) += integrity_audit.o
integrity-$(CONFIG_INTEGRITY_SIGNATURE) += digsig.o
integrity-$(CONFIG_INTEGRITY_ASYMMETRIC_KEYS) += digsig_asymmetric.o
integrity-$(CONFIG_INTEGRITY_PLATFORM_KEYRING) += platform_certs/platform_keyring.o
+integrity-$(CONFIG_INTEGRITY_MOK_KEYRING) += platform_certs/mok_keyring.o
integrity-$(CONFIG_LOAD_UEFI_KEYS) += platform_certs/efi_parser.o \
platform_certs/load_uefi.o \
platform_certs/keyring_handler.o
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index 3b06a01bd0fd..e07334504ef1 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -30,6 +30,7 @@ static const char * const keyring_name[INTEGRITY_KEYRING_MAX] = {
".ima",
#endif
".platform",
+ ".mok",
};

#ifdef CONFIG_IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index 547425c20e11..be56ba49dc19 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -151,7 +151,8 @@ int integrity_kernel_read(struct file *file, loff_t offset,
#define INTEGRITY_KEYRING_EVM 0
#define INTEGRITY_KEYRING_IMA 1
#define INTEGRITY_KEYRING_PLATFORM 2
-#define INTEGRITY_KEYRING_MAX 3
+#define INTEGRITY_KEYRING_MOK 3
+#define INTEGRITY_KEYRING_MAX 4

extern struct dentry *integrity_dir;

@@ -283,3 +284,12 @@ static inline void __init add_to_platform_keyring(const char *source,
{
}
#endif
+
+#ifdef CONFIG_INTEGRITY_MOK_KEYRING
+void __init add_to_mok_keyring(const char *source, const void *data, size_t len);
+#else
+static inline void __init add_to_mok_keyring(const char *source,
+ const void *data, size_t len)
+{
+}
+#endif
diff --git a/security/integrity/platform_certs/mok_keyring.c b/security/integrity/platform_certs/mok_keyring.c
new file mode 100644
index 000000000000..bcd9ac78ce3b
--- /dev/null
+++ b/security/integrity/platform_certs/mok_keyring.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * MOK keyring routines.
+ *
+ * Copyright (c) 2021, Oracle and/or its affiliates.
+ */
+
+#include "../integrity.h"
+
+static __init int mok_keyring_init(void)
+{
+ int rc;
+
+ rc = integrity_init_keyring(INTEGRITY_KEYRING_MOK);
+ if (rc)
+ return rc;
+
+ pr_notice("MOK Keyring initialized\n");
+ return 0;
+}
+device_initcall(mok_keyring_init);
+
+void __init add_to_mok_keyring(const char *source, const void *data, size_t len)
+{
+ key_perm_t perm;
+ int rc;
+
+ perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW;
+ rc = integrity_load_cert(INTEGRITY_KEYRING_MOK, source, data, len, perm);
+
+ /*
+ * Some MOKList keys may not pass the mok keyring restrictions.
+ * If the restriction check does not pass and the platform keyring
+ * is configured, try to add it into that keyring instead.
+ */
+ if (rc)
+ rc = integrity_load_cert(INTEGRITY_KEYRING_PLATFORM, source,
+ data, len, perm);
+
+ if (rc)
+ pr_info("Error adding keys to mok keyring %s\n", source);
+}
--
2.18.4