rootcert.c

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/*
 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
FILE_SECBOOT ( PERMITTED );

#include <stdlib.h>
#include <ipxe/crypto.h>
#include <ipxe/sha256.h>
#include <ipxe/x509.h>
#include <ipxe/settings.h>
#include <ipxe/dhcp.h>
#include <ipxe/init.h>
#include <ipxe/rootcert.h>

/** @file
 *
 * Root certificate store
 *
 */

/** Length of a root certificate fingerprint */
#define FINGERPRINT_LEN SHA256_DIGEST_SIZE

/* Allow trusted certificates to be overridden if not explicitly specified */
#ifndef ALLOW_TRUST_OVERRIDE
 #ifdef TRUSTED
  #define ALLOW_TRUST_OVERRIDE 0
 #else
  #define ALLOW_TRUST_OVERRIDE 1
 #endif
#endif

/* Use iPXE root CA if no trusted certificates are explicitly specified */
#ifndef TRUSTED
#define TRUSTED                                                         \
        /* iPXE root CA */                                              \
        0x9f, 0xaf, 0x71, 0x7b, 0x7f, 0x8c, 0xa2, 0xf9, 0x3c, 0x25,     \
        0x6c, 0x79, 0xf8, 0xac, 0x55, 0x91, 0x89, 0x5d, 0x66, 0xd1,     \
        0xff, 0x3b, 0xee, 0x63, 0x97, 0xa7, 0x0d, 0x29, 0xc6, 0x5e,     \
        0xed, 0x1a,
#endif

/** Flag indicating if root of trust may be overridden at runtime */
const int allow_trust_override = ALLOW_TRUST_OVERRIDE;

/** Root certificate fingerprints */
static const uint8_t fingerprints[] = { TRUSTED };

/** Root certificate fingerprint setting */
static struct setting trust_setting __setting ( SETTING_CRYPTO, trust ) = {
        .name = "trust",
        .description = "Trusted root certificate fingerprints",
        .tag = DHCP_EB_TRUST,
        .type = &setting_type_hex,
};

/** Root certificates */
struct x509_root root_certificates = {
        .refcnt = REF_INIT ( ref_no_free ),
        .digest = &sha256_algorithm,
        .count = ( sizeof ( fingerprints ) / FINGERPRINT_LEN ),
        .fingerprints = fingerprints,
};

/**
 * Initialise root certificate
 *
 * The list of trusted root certificates can be specified at build
 * time using the TRUST= build parameter.  If no certificates are
 * specified, then the default iPXE root CA certificate is trusted.
 *
 * If no certificates were explicitly specified, then we allow the
 * list of trusted root certificate fingerprints to be overridden
 * using the "trust" setting, but only at the point of iPXE
 * initialisation.  This prevents untrusted sources of settings
 * (e.g. DHCP) from subverting the chain of trust, while allowing
 * trustworthy sources (e.g. VMware GuestInfo or non-volatile stored
 * options) to specify the trusted root certificate without requiring
 * a rebuild.
 */
static void rootcert_init ( void ) {
        static int initialised;
        void *external = NULL;
        int len;

        /* Allow trusted root certificates to be overridden only if
         * not explicitly specified at build time.
         */
        if ( ALLOW_TRUST_OVERRIDE && ( ! initialised ) ) {

                /* Fetch copy of "trust" setting, if it exists.  This
                 * memory will never be freed.
                 */
                if ( ( len = fetch_raw_setting_copy ( NULL, &trust_setting,
                                                      &external ) ) >= 0 ) {
                        root_certificates.fingerprints = external;
                        root_certificates.count = ( len / FINGERPRINT_LEN );
                }

                /* Prevent subsequent modifications */
                initialised = 1;
        }

        DBGC ( &root_certificates, "ROOTCERT using %d %s certificate(s):\n",
               root_certificates.count, ( external ? "external" : "built-in" ));
        DBGC_HDA ( &root_certificates, 0, root_certificates.fingerprints,
                   ( root_certificates.count * FINGERPRINT_LEN ) );
}

/** Root certificate initialiser */
struct startup_fn rootcert_startup_fn __startup_fn ( STARTUP_LATE ) = {
        .name = "rootcert",
        .startup = rootcert_init,
};