efi: Import certificates from UEFI Secure Boot

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.

[zohar@linux.ibm.com: dropped Josh's original patch description]
Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

2 files changed, 173 insertions, 1 deletions

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..8ceafa58d98c
--- /dev/null
+++ b/security/integrity/platform_certs/load_uefi.c
@@ -0,0 +1,169 @@
+// 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 a hash.
+ */
+static __init void uefi_blacklist_hash(const char *source, const void *data,
+                                       size_t len, const char *type,
+                                       size_t type_len)
+{
+        char *hash, *p;
+
+        hash = kmalloc(type_len + len * 2 + 1, GFP_KERNEL);
+        if (!hash)
+                return;
+        p = memcpy(hash, type, type_len);
+        p += type_len;
+        bin2hex(p, data, len);
+        p += len * 2;
+        *p = 0;
+
+        mark_hash_blacklisted(hash);
+        kfree(hash);
+}
+
+/*
+ * Blacklist an X509 TBS hash.
+ */
+static __init void uefi_blacklist_x509_tbs(const char *source,
+                                           const void *data, size_t len)
+{
+        uefi_blacklist_hash(source, data, len, "tbs:", 4);
+}
+
+/*
+ * Blacklist the hash of an executable.
+ */
+static __init void uefi_blacklist_binary(const char *source,
+                                         const void *data, size_t len)
+{
+        uefi_blacklist_hash(source, data, len, "bin:", 4);
+}
+
+/*
+ * 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);