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// 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 <crypto/hash.h>
#include <keys/system_keyring.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;
}
static int mod_is_hash_blacklisted(const void *mod, size_t verifylen)
{
struct crypto_shash *tfm;
struct shash_desc *desc;
size_t digest_size, desc_size;
u8 *digest;
int ret;
tfm = crypto_alloc_shash("sha256", 0, 0);
if (IS_ERR(tfm)) {
ret = PTR_ERR(tfm);
goto error_return;
}
desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
digest_size = crypto_shash_digestsize(tfm);
digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
if (!digest) {
pr_err("digest memory buffer allocate fail\n");
ret = -ENOMEM;
goto error_digest;
}
desc = (void *)digest + digest_size;
desc->tfm = tfm;
ret = crypto_shash_init(desc);
if (ret < 0)
goto error_shash;
ret = crypto_shash_finup(desc, mod, verifylen, digest);
if (ret < 0)
goto error_shash;
pr_debug("%ld digest: %*phN\n", verifylen, (int) digest_size, digest);
ret = is_hash_blacklisted(digest, digest_size, BLACKLIST_HASH_BINARY);
if (ret == -EKEYREJECTED)
pr_err("Module hash %*phN is blacklisted\n",
(int) digest_size, digest);
error_shash:
kfree(digest);
error_digest:
crypto_free_shash(tfm);
error_return:
return ret;
}
/*
* 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, wholelen;
int ret;
pr_devel("==>%s(,%zu)\n", __func__, modlen);
if (modlen <= sizeof(ms))
return -EBADMSG;
wholelen = modlen + sizeof(MODULE_SIG_STRING) - 1;
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;
ret = verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
VERIFY_USE_SECONDARY_KEYRING,
VERIFYING_MODULE_SIGNATURE,
NULL, NULL);
pr_devel("verify_pkcs7_signature() = %d\n", ret);
if (ret == -ENOKEY && IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING)) {
ret = verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
VERIFY_USE_PLATFORM_KEYRING,
VERIFYING_MODULE_SIGNATURE,
NULL, NULL);
pr_devel("verify_pkcs7_signature() = %d\n", ret);
}
/* checking hash of module is in blacklist */
if (!ret)
ret = mod_is_hash_blacklisted(mod, wholelen);
return ret;
}
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);
}
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