| From 90dc66270b02981b19a085c6a9184e3452b7b3e8 Mon Sep 17 00:00:00 2001 |
| From: Josh Boyer <jwboyer@fedoraproject.org> |
| Date: Fri, 5 May 2017 08:21:59 +0100 |
| Subject: [PATCH 3/4] MODSIGN: Import certificates from UEFI Secure Boot |
| |
| 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@fedoraproject.org> |
| Signed-off-by: David Howells <dhowells@redhat.com> |
| |
| certs/Kconfig | 16 ++++++ |
| certs/Makefile | 4 ++ |
| certs/load_uefi.c | 168 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
| 3 files changed, 188 insertions(+) |
| create mode 100644 certs/load_uefi.c |
| |
| diff --git a/certs/Kconfig b/certs/Kconfig |
| index 630ae09..edf9f75 100644 |
| |
| |
| @@ -90,4 +90,20 @@ config EFI_SIGNATURE_LIST_PARSER |
| This option provides support for parsing EFI signature lists for |
| X.509 certificates and turning them into keys. |
| |
| +config LOAD_UEFI_KEYS |
| + bool "Load certs and blacklist from UEFI db for module checking" |
| + depends on SYSTEM_BLACKLIST_KEYRING |
| + depends on SECONDARY_TRUSTED_KEYRING |
| + depends on EFI |
| + depends on EFI_SIGNATURE_LIST_PARSER |
| + help |
| + If the kernel is booted in secure boot mode, this option will cause |
| + the kernel to load the certificates from the UEFI db and MokListRT |
| + into the secondary trusted keyring. It will also load any X.509 |
| + SHA256 hashes in the dbx list into the blacklist. |
| + |
| + The effect of this is that, if the kernel is booted in secure boot |
| + mode, modules signed with UEFI-stored keys will be permitted to be |
| + loaded and keys that match the blacklist will be rejected. |
| + |
| endmenu |
| diff --git a/certs/Makefile b/certs/Makefile |
| index 738151a..a5e057a 100644 |
| |
| |
| @@ -11,6 +11,10 @@ obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist_nohashes.o |
| endif |
| obj-$(CONFIG_EFI_SIGNATURE_LIST_PARSER) += efi_parser.o |
| |
| +obj-$(CONFIG_LOAD_UEFI_KEYS) += load_uefi.o |
| +$(obj)/load_uefi.o: KBUILD_CFLAGS += -fshort-wchar |
| + |
| + |
| ifeq ($(CONFIG_SYSTEM_TRUSTED_KEYRING),y) |
| |
| $(eval $(call config_filename,SYSTEM_TRUSTED_KEYS)) |
| diff --git a/certs/load_uefi.c b/certs/load_uefi.c |
| new file mode 100644 |
| index 0000000..b44e464 |
| |
| |
| @@ -0,0 +1,168 @@ |
| +#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 "internal.h" |
| + |
| +static __initdata efi_guid_t efi_cert_x509_guid = EFI_CERT_X509_GUID; |
| +static __initdata efi_guid_t efi_cert_x509_sha256_guid = EFI_CERT_X509_SHA256_GUID; |
| +static __initdata efi_guid_t efi_cert_sha256_guid = 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) { |
| + pr_err("Couldn't allocate memory for uefi cert list\n"); |
| + 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_trusted_secondary_key; |
| + 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("MODSIGN: 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("MODSIGN: 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("MODSIGN: 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); |
| -- |
| 2.9.3 |
| |