[PATCH v2 5/7] efi: Import certificates from UEFI Secure Boot

[Nayna Jain]

From: Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx>

New Patch Description:
======================

Secure Boot stores a list of allowed certificates in the 'db' variable.
This patch imports those certificates into the platform keyring. The shim
UEFI bootloader has a similar certificate list stored in the 'MokListRT'
variable. We import those as well.

Secure Boot also maintains a list of disallowed certificates in the 'dbx'
variable. We load those certificates into the system blacklist keyring
and forbid any kernel signed with those from loading.

Original Patch Description:
============================

Secure Boot stores a list of allowed certificates in the 'db' variable.
This imports those certificates into the system trusted keyring.  This
allows for a third party signing certificate to be used in conjunction
with signed modules. By importing the public certificate into the 'db'
variable, a user can allow a module signed with that certificate to
load. The shim UEFI bootloader has a similar certificate list stored
in the 'MokListRT' variable. We import those as well.

Secure Boot also maintains a list of disallowed certificates in the 'dbx'
variable. We load those certificates into the newly introduced system
blacklist keyring and forbid any module signed with those from loading and
forbid the use within the kernel of any key with a matching hash.

This facility is enabled by setting CONFIG_LOAD_UEFI_KEYS.

Signed-off-by: Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxx>
Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
---
Changelog:

v0:
- This patch replaces the loading of certificates onto the secondary
  keyring with platform keyring
- removed the CONFIG LOAD_UEFI_KEYS
- moved the file load_uefi.o from certs to security/integrity/platform_certs

v2:
- Fixed the checkpatch.pl warnings

 security/integrity/Makefile                   |   5 +-
 security/integrity/platform_certs/load_uefi.c | 171 ++++++++++++++++++++++++++
 2 files changed, 175 insertions(+), 1 deletion(-)
 create mode 100644 security/integrity/platform_certs/load_uefi.c

diff --git a/security/integrity/Makefile b/security/integrity/Makefile
index 6ee9058866cd..86df9aba8c0f 100644
--- a/security/integrity/Makefile
+++ b/security/integrity/Makefile
@@ -10,7 +10,10 @@ 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 \
-						  platform_certs/efi_parser.o
+						  platform_certs/efi_parser.o \
+						  platform_certs/load_uefi.o
+obj-$(CONFIG_LOAD_UEFI_KEYS) += platform_certs/load_uefi.o
+$(obj)/load_uefi.o: KBUILD_CFLAGS += -fshort-wchar
 
 subdir-$(CONFIG_IMA)			+= ima
 obj-$(CONFIG_IMA)			+= ima/
diff --git a/security/integrity/platform_certs/load_uefi.c b/security/integrity/platform_certs/load_uefi.c
new file mode 100644
index 000000000000..acd9db90dde7
--- /dev/null
+++ b/security/integrity/platform_certs/load_uefi.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/cred.h>
+#include <linux/err.h>
+#include <linux/efi.h>
+#include <linux/slab.h>
+#include <keys/asymmetric-type.h>
+#include <keys/system_keyring.h>
+#include "../integrity.h"
+
+static efi_guid_t efi_cert_x509_guid __initdata = EFI_CERT_X509_GUID;
+static efi_guid_t efi_cert_x509_sha256_guid __initdata =
+	EFI_CERT_X509_SHA256_GUID;
+static efi_guid_t efi_cert_sha256_guid __initdata = EFI_CERT_SHA256_GUID;
+
+/*
+ * Get a certificate list blob from the named EFI variable.
+ */
+static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
+				  unsigned long *size)
+{
+	efi_status_t status;
+	unsigned long lsize = 4;
+	unsigned long tmpdb[4];
+	void *db;
+
+	status = efi.get_variable(name, guid, NULL, &lsize, &tmpdb);
+	if (status != EFI_BUFFER_TOO_SMALL) {
+		pr_err("Couldn't get size: 0x%lx\n", status);
+		return NULL;
+	}
+
+	db = kmalloc(lsize, GFP_KERNEL);
+	if (!db)
+		return NULL;
+
+	status = efi.get_variable(name, guid, NULL, &lsize, db);
+	if (status != EFI_SUCCESS) {
+		kfree(db);
+		pr_err("Error reading db var: 0x%lx\n", status);
+		return NULL;
+	}
+
+	*size = lsize;
+	return db;
+}
+
+/*
+ * Blacklist an X509 TBS hash.
+ */
+static __init void uefi_blacklist_x509_tbs(const char *source,
+					   const void *data, size_t len)
+{
+	char *hash, *p;
+
+	hash = kmalloc(4 + len * 2 + 1, GFP_KERNEL);
+	if (!hash)
+		return;
+	p = memcpy(hash, "tbs:", 4);
+	p += 4;
+	bin2hex(p, data, len);
+	p += len * 2;
+	*p = 0;
+
+	mark_hash_blacklisted(hash);
+	kfree(hash);
+}
+
+/*
+ * Blacklist the hash of an executable.
+ */
+static __init void uefi_blacklist_binary(const char *source,
+					 const void *data, size_t len)
+{
+	char *hash, *p;
+
+	hash = kmalloc(4 + len * 2 + 1, GFP_KERNEL);
+	if (!hash)
+		return;
+	p = memcpy(hash, "bin:", 4);
+	p += 4;
+	bin2hex(p, data, len);
+	p += len * 2;
+	*p = 0;
+
+	mark_hash_blacklisted(hash);
+	kfree(hash);
+}
+
+/*
+ * Return the appropriate handler for particular signature list types found in
+ * the UEFI db and MokListRT tables.
+ */
+static __init efi_element_handler_t get_handler_for_db(const efi_guid_t *
+						       sig_type)
+{
+	if (efi_guidcmp(*sig_type, efi_cert_x509_guid) == 0)
+		return add_to_platform_keyring;
+	return 0;
+}
+
+/*
+ * Return the appropriate handler for particular signature list types found in
+ * the UEFI dbx and MokListXRT tables.
+ */
+static __init efi_element_handler_t get_handler_for_dbx(const efi_guid_t *
+							sig_type)
+{
+	if (efi_guidcmp(*sig_type, efi_cert_x509_sha256_guid) == 0)
+		return uefi_blacklist_x509_tbs;
+	if (efi_guidcmp(*sig_type, efi_cert_sha256_guid) == 0)
+		return uefi_blacklist_binary;
+	return 0;
+}
+
+/*
+ * Load the certs contained in the UEFI databases
+ */
+static int __init load_uefi_certs(void)
+{
+	efi_guid_t secure_var = EFI_IMAGE_SECURITY_DATABASE_GUID;
+	efi_guid_t mok_var = EFI_SHIM_LOCK_GUID;
+	void *db = NULL, *dbx = NULL, *mok = NULL;
+	unsigned long dbsize = 0, dbxsize = 0, moksize = 0;
+	int rc = 0;
+
+	if (!efi.get_variable)
+		return false;
+
+	/* Get db, MokListRT, and dbx.  They might not exist, so it isn't
+	 * an error if we can't get them.
+	 */
+	db = get_cert_list(L"db", &secure_var, &dbsize);
+	if (!db) {
+		pr_err("Couldn't get UEFI db list\n");
+	} else {
+		rc = parse_efi_signature_list("UEFI:db",
+					      db, dbsize, get_handler_for_db);
+		if (rc)
+			pr_err("Couldn't parse db signatures: %d\n", rc);
+		kfree(db);
+	}
+
+	mok = get_cert_list(L"MokListRT", &mok_var, &moksize);
+	if (!mok) {
+		pr_info("Couldn't get UEFI MokListRT\n");
+	} else {
+		rc = parse_efi_signature_list("UEFI:MokListRT",
+					      mok, moksize, get_handler_for_db);
+		if (rc)
+			pr_err("Couldn't parse MokListRT signatures: %d\n", rc);
+		kfree(mok);
+	}
+
+	dbx = get_cert_list(L"dbx", &secure_var, &dbxsize);
+	if (!dbx) {
+		pr_info("Couldn't get UEFI dbx list\n");
+	} else {
+		rc = parse_efi_signature_list("UEFI:dbx",
+					      dbx, dbxsize,
+					      get_handler_for_dbx);
+		if (rc)
+			pr_err("Couldn't parse dbx signatures: %d\n", rc);
+		kfree(dbx);
+	}
+
+	return rc;
+}
+late_initcall(load_uefi_certs);
-- 
2.13.6