// SPDX-License-Identifier: GPL-2.0-or-later
/* Module signature checker
 *
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/module_signature.h>
#include <linux/string.h>
#include <linux/verification.h>
#include <linux/security.h>
#include <crypto/public_key.h>
#include <uapi/linux/module.h>
#include "internal.h"

#undef MODULE_PARAM_PREFIX
#define MODULE_PARAM_PREFIX "module."

static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE);
module_param(sig_enforce, bool_enable_only, 0644);

/*
 * Export sig_enforce kernel cmdline parameter to allow other subsystems rely
 * on that instead of directly to CONFIG_MODULE_SIG_FORCE config.
 */
bool is_module_sig_enforced(void)
{
        return sig_enforce;
}
EXPORT_SYMBOL(is_module_sig_enforced);

void set_module_sig_enforced(void)
{
        sig_enforce = true;
}

/*
 * Verify the signature on a module.
 */
int mod_verify_sig(const void *mod, struct load_info *info)
{
        struct module_signature ms;
        size_t sig_len, modlen = info->len;
        int ret;

        pr_devel("==>%s(,%zu)\n", __func__, modlen);

        if (modlen <= sizeof(ms))
                return -EBADMSG;

        memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));

        ret = mod_check_sig(&ms, modlen, "module");
        if (ret)
                return ret;

        sig_len = be32_to_cpu(ms.sig_len);
        modlen -= sig_len + sizeof(ms);
        info->len = modlen;

        return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
                                      VERIFY_USE_SECONDARY_KEYRING,
                                      VERIFYING_MODULE_SIGNATURE,
                                      NULL, NULL);
}

int module_sig_check(struct load_info *info, int flags)
{
        int err = -ENODATA;
        const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
        const char *reason;
        const void *mod = info->hdr;
        bool mangled_module = flags & (MODULE_INIT_IGNORE_MODVERSIONS |
                                       MODULE_INIT_IGNORE_VERMAGIC);
        /*
         * Do not allow mangled modules as a module with version information
         * removed is no longer the module that was signed.
         */
        if (!mangled_module &&
            info->len > markerlen &&
            memcmp(mod + info->len - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
                /* We truncate the module to discard the signature */
                info->len -= markerlen;
                err = mod_verify_sig(mod, info);
                if (!err) {
                        info->sig_ok = true;
                        return 0;
                }
        }

        /*
         * We don't permit modules to be loaded into the trusted kernels
         * without a valid signature on them, but if we're not enforcing,
         * certain errors are non-fatal.
         */
        switch (err) {
        case -ENODATA:
                reason = "unsigned module";
                break;
        case -ENOPKG:
                reason = "module with unsupported crypto";
                break;
        case -ENOKEY:
                reason = "module with unavailable key";
                break;

        default:
                /*
                 * All other errors are fatal, including lack of memory,
                 * unparseable signatures, and signature check failures --
                 * even if signatures aren't required.
                 */
                return err;
        }

        if (is_module_sig_enforced()) {
                pr_notice("Loading of %s is rejected\n", reason);
                return -EKEYREJECTED;
        }

        return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
}