load_uefi.c
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// 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;
/*
* Look to see if a UEFI variable called MokIgnoreDB exists and return true if
* it does.
*
* This UEFI variable is set by the shim if a user tells the shim to not use
* the certs/hashes in the UEFI db variable for verification purposes. If it
* is set, we should ignore the db variable also and the true return indicates
* this.
*/
static __init bool uefi_check_ignore_db(void)
{
efi_status_t status;
unsigned int db = 0;
unsigned long size = sizeof(db);
efi_guid_t guid = EFI_SHIM_LOCK_GUID;
status = efi.get_variable(L"MokIgnoreDB", &guid, NULL, &size, &db);
return status == EFI_SUCCESS;
}
/*
* 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 into the platform trusted
* keyring and the UEFI blacklisted X.509 cert SHA256 hashes into the blacklist
* keyring.
*/
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.
*/
if (!uefi_check_ignore_db()) {
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("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);