Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   ebiederm@xmission.com (Eric W. Biederman)
To:     David Howells <dhowells@redhat.com>
Cc:     torvalds@linux-foundation.org, linux-man@vger.kernel.org,
        linux-api@vger.kernel.org, jmorris@namei.org,
        linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org
References: <152346387861.4030.4408662483445703127.stgit@warthog.procyon.org.uk>
        <152346391877.4030.6270466586590461223.stgit@warthog.procyon.org.uk>
Date:   Wed, 11 Apr 2018 14:00:17 -0500
In-Reply-To: <152346391877.4030.6270466586590461223.stgit@warthog.procyon.org.uk>
        (David Howells's message of "Wed, 11 Apr 2018 17:25:18 +0100")
Message-ID: <87po35k1q6.fsf@xmission.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

David Howells <dhowells@redhat.com> writes:

> From: Matthew Garrett <mjg59@srcf.ucam.org>
>
> The kexec_load() syscall permits the loading and execution of arbitrary
> code in ring 0, which is something that lock-down is meant to prevent. It
> makes sense to disable kexec_load() in this situation.
>
> This does not affect kexec_file_load() syscall which can check for a
> signature on the image to be booted.

Maybing I am missing it but I am not seeing anything that would require
kexec_file_load be configured such that it checks the loaded kernel.

Without that I don't see the point of disabling kexec_load.

Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>


Eric


> Signed-off-by: Matthew Garrett <mjg59@srcf.ucam.org>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Acked-by: Dave Young <dyoung@redhat.com>
> Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
> Reviewed-by: James Morris <james.l.morris@oracle.com>
> cc: kexec@lists.infradead.org
> ---
>
>  kernel/kexec.c |    7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index aed8fb2564b3..1553ac765e73 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -199,6 +199,13 @@ static inline int kexec_load_check(unsigned long nr_segments,
>  	if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
>  		return -EPERM;
>  
> +	/*
> +	 * kexec can be used to circumvent module loading restrictions, so
> +	 * prevent loading in that case
> +	 */
> +	if (kernel_is_locked_down("kexec of unsigned images"))
> +		return -EPERM;
> +
>  	/*
>  	 * Verify we have a legal set of flags
>  	 * This leaves us room for future extensions.