From: Josh Boyer <jwboyer@xxxxxxxxxx>
Secure Boot stores a list of allowed certificates in the 'db' variable.
This imports those certificates into the module signing 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.
In the opposite case, Secure Boot maintains a list of disallowed
certificates in the 'dbx' variable. We load those certificates into
the newly introduced module blacklist keyring and forbid any module
signed with those from loading.
Signed-off-by: Josh Boyer <jwboyer@xxxxxxxxxx>
---
include/linux/efi.h | 6 ++++
init/Kconfig | 9 ++++++
kernel/Makefile | 3 ++
kernel/modsign_uefi.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 108 insertions(+)
create mode 100644 kernel/modsign_uefi.c
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 64b3e55..76fe526 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -394,6 +394,12 @@ typedef efi_status_t efi_query_capsule_caps_t(efi_capsule_header_t **capsules,
#define EFI_CERT_X509_GUID \
EFI_GUID( 0xa5c059a1, 0x94e4, 0x4aa7, 0x87, 0xb5, 0xab, 0x15, 0x5c, 0x2b, 0xf0, 0x72 )
+#define EFI_IMAGE_SECURITY_DATABASE_GUID \
+ EFI_GUID( 0xd719b2cb, 0x3d3a, 0x4596, 0xa3, 0xbc, 0xda, 0xd0, 0x0e, 0x67, 0x65, 0x6f )
+
+#define EFI_SHIM_LOCK_GUID \
+ EFI_GUID( 0x605dab50, 0xe046, 0x4300, 0xab, 0xb6, 0x3d, 0xd8, 0x10, 0xdd, 0x8b, 0x23 )
+
typedef struct {
efi_guid_t guid;
u64 table;
diff --git a/init/Kconfig b/init/Kconfig
index d972b77..27e3a82 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1673,6 +1673,15 @@ config MODULE_SIG_BLACKLIST
should not pass module signature verification. If a module is
signed with something in this keyring, the load will be rejected.
+config MODULE_SIG_UEFI
+ bool "Allow modules signed with certs stored in UEFI"
+ depends on MODULE_SIG && MODULE_SIG_BLACKLIST && EFI
+ select EFI_SIGNATURE_LIST_PARSER
+ help
+ This will import certificates stored in UEFI and allow modules
+ signed with those to be loaded. It will also disallow loading
+ of modules stored in the UEFI dbx variable.
+
choice
prompt "Which hash algorithm should modules be signed with?"
depends on MODULE_SIG
diff --git a/kernel/Makefile b/kernel/Makefile
index 6c072b6..8848829 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -55,6 +55,7 @@ obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
obj-$(CONFIG_UID16) += uid16.o
obj-$(CONFIG_MODULES) += module.o
obj-$(CONFIG_MODULE_SIG) += module_signing.o modsign_pubkey.o modsign_certificate.o
+obj-$(CONFIG_MODULE_SIG_UEFI) += modsign_uefi.o
obj-$(CONFIG_KALLSYMS) += kallsyms.o
obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
obj-$(CONFIG_KEXEC) += kexec.o
@@ -114,6 +115,8 @@ obj-$(CONFIG_CONTEXT_TRACKING) += context_tracking.o
$(obj)/configs.o: $(obj)/config_data.h
+$(obj)/modsign_uefi.o: KBUILD_CFLAGS += -fshort-wchar
+
# config_data.h contains the same information as ikconfig.h but gzipped.
# Info from config_data can be extracted from /proc/config*
targets += config_data.gz
diff --git a/kernel/modsign_uefi.c b/kernel/modsign_uefi.c
new file mode 100644
index 0000000..b9237d7
--- /dev/null
+++ b/kernel/modsign_uefi.c
@@ -0,0 +1,90 @@
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/cred.h>
+#include <linux/err.h>
+#include <linux/efi.h>
+#include <keys/asymmetric-type.h>
+#include "module-internal.h"
+
+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 = NULL;
+
+ 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) {
+ pr_err("Couldn't allocate memory for uefi cert list\n");
+ goto out;
+ }
+
+ status = efi.get_variable(name, guid, NULL, &lsize, db);
+ if (status != EFI_SUCCESS) {
+ kfree(db);
+ db = NULL;
+ pr_err("Error reading db var: 0x%lx\n", status);
+ }
+out:
+ *size = lsize;
+ return db;
+}
+
+/*
+ * * 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;
+
+ /* Check if SB is enabled and just return if not */
+ if (!efi_enabled(EFI_SECURE_BOOT))
+ return 0;
+
+ /* 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("MODSIGN: Couldn't get UEFI db list\n");
+ } else {
+ rc = parse_efi_signature_list(db, dbsize, modsign_keyring);
+ 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("MODSIGN: Couldn't get UEFI MokListRT\n");
+ } else {
+ rc = parse_efi_signature_list(mok, moksize, modsign_keyring);
+ 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("MODSIGN: Couldn't get UEFI dbx list\n");
+ } else {
+ rc = parse_efi_signature_list(dbx, dbxsize,
+ modsign_blacklist);
+ if (rc)
+ pr_err("Couldn't parse dbx signatures: %d\n", rc);
+ kfree(dbx);
+ }
+
+ return rc;
+}
+late_initcall(load_uefi_certs);
--
1.8.0.2
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