linux-kernel - Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

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Date:   Wed, 11 Apr 2018 16:09:35 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        David Howells <dhowells@...hat.com>
Cc:     torvalds@...ux-foundation.org, linux-man@...r.kernel.org,
        linux-api@...r.kernel.org, jmorris@...ei.org,
        linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is
 locked down

On Wed, 2018-04-11 at 14:00 -0500, Eric W. Biederman wrote:
> David Howells <dhowells@...hat.com> writes:
> 
> > From: Matthew Garrett <mjg59@...f.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@...ssion.com>

The IMA "secure boot" policy requires the kexec image to be signed.
 This call to kernel_is_locked_down() could be replaced with a call
to security_kernel_read_file(NULL, READING_KEXEC_IMAGE).

It would be similar to the existing init_module syscall calling
security_kernel_read_file().

Mimi