Commit 49fcf732 authored by David Howells's avatar David Howells Committed by James Morris
Browse files

lockdown: Enforce module signatures if the kernel is locked down 



If the kernel is locked down, require that all modules have valid
signatures that we can verify.

I have adjusted the errors generated:

 (1) If there's no signature (ENODATA) or we can't check it (ENOPKG,
     ENOKEY), then:

     (a) If signatures are enforced then EKEYREJECTED is returned.

     (b) If there's no signature or we can't check it, but the kernel is
	 locked down then EPERM is returned (this is then consistent with
	 other lockdown cases).

 (2) If the signature is unparseable (EBADMSG, EINVAL), the signature fails
     the check (EKEYREJECTED) or a system error occurs (eg. ENOMEM), we
     return the error we got.

Note that the X.509 code doesn't check for key expiry as the RTC might not
be valid or might not have been transferred to the kernel's clock yet.

 [Modified by Matthew Garrett to remove the IMA integration. This will
  be replaced with integration with the IMA architecture policy
  patchset.]

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarMatthew Garrett <matthewgarrett@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Cc: Jessica Yu <jeyu@kernel.org>
Signed-off-by: default avatarJames Morris <jmorris@namei.org>
parent 000d388e

include/linux/security.h

+1 −0
Original line number Diff line number Diff line
@@ -103,6 +103,7 @@ enum lsm_event { 
 */

enum lockdown_reason {

	LOCKDOWN_NONE,

	LOCKDOWN_MODULE_SIGNATURE,

	LOCKDOWN_INTEGRITY_MAX,

	LOCKDOWN_CONFIDENTIALITY_MAX,

};

init/Kconfig

+5 −0
Original line number Diff line number Diff line
@@ -1939,6 +1939,11 @@ config MODULE_SIG 
	  kernel build dependency so that the signing tool can use its crypto

	  library.



	  You should enable this option if you wish to use either

	  CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via

	  another LSM - otherwise unsigned modules will be loadable regardless

	  of the lockdown policy.



	  !!!WARNING!!!  If you enable this option, you MUST make sure that the

	  module DOES NOT get stripped after being signed.  This includes the

	  debuginfo strip done by some packagers (such as rpmbuild) and

kernel/module.c

+30 −7
Original line number Diff line number Diff line
@@ -2753,8 +2753,9 @@ static inline void kmemleak_load_module(const struct module *mod, 
#ifdef CONFIG_MODULE_SIG

static int module_sig_check(struct load_info *info, int flags)

{

	int err = -ENOKEY;

	int err = -ENODATA;

	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;

	const char *reason;

	const void *mod = info->hdr;



	/*
@@ -2769,17 +2770,39 @@ static int module_sig_check(struct load_info *info, int flags) 
		err = mod_verify_sig(mod, info);

	}



	if (!err) {

	switch (err) {

	case 0:

		info->sig_ok = true;

		return 0;

	}



	/* Not having a signature is only an error if we're strict. */

	if (err == -ENOKEY && !is_module_sig_enforced())

		err = 0;



		/* We don't permit modules to be loaded into trusted kernels

		 * without a valid signature on them, but if we're not

		 * enforcing, certain errors are non-fatal.

		 */

	case -ENODATA:

		reason = "Loading of unsigned module";

		goto decide;

	case -ENOPKG:

		reason = "Loading of module with unsupported crypto";

		goto decide;

	case -ENOKEY:

		reason = "Loading of module with unavailable key";

	decide:

		if (is_module_sig_enforced()) {

			pr_notice("%s is rejected\n", reason);

			return -EKEYREJECTED;

		}



		return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);



		/* All other errors are fatal, including nomem, unparseable

		 * signatures and signature check failures - even if signatures

		 * aren't required.

		 */

	default:

		return err;

	}

}

#else /* !CONFIG_MODULE_SIG */

static int module_sig_check(struct load_info *info, int flags)

{

security/lockdown/Kconfig

+1 −0
Original line number Diff line number Diff line 
config SECURITY_LOCKDOWN_LSM

	bool "Basic module for enforcing kernel lockdown"

	depends on SECURITY

	select MODULE_SIG if MODULES

	help

	  Build support for an LSM that enforces a coarse kernel lockdown

	  behaviour.

security/lockdown/lockdown.c

+1 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ static enum lockdown_reason kernel_locked_down; 


static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {

	[LOCKDOWN_NONE] = "none",

	[LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading",

	[LOCKDOWN_INTEGRITY_MAX] = "integrity",

	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",

};

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