linux-kernel - Re: [PATCH 09/24] kexec_file: Disable at runtime if securelevel has been set

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Date:   Fri, 07 Apr 2017 08:07:55 +0100
From:   David Howells <dhowells@...hat.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     dhowells@...hat.com, Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org,
        Matthew Garrett <mjg59@...f.ucam.org>,
        linux-efi@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
        Chun-Yi Lee <jlee@...e.com>, gregkh@...uxfoundation.org,
        kexec@...ts.infradead.org, linux-security-module@...r.kernel.org,
        keyrings@...r.kernel.org, matthew.garrett@...ula.com
Subject: Re: [PATCH 09/24] kexec_file: Disable at runtime if securelevel has been set

Dave Young <dyoung@...hat.com> wrote:

> > > > +	/* Don't permit images to be loaded into trusted kernels if we're not
> > > > +	 * going to verify the signature on them
> > > > +	 */
> > > > +	if (!IS_ENABLED(CONFIG_KEXEC_VERIFY_SIG) && kernel_is_locked_down())
> > > > +		return -EPERM;
> > > > +
> > > >  
> > 
> > IMA can be used to verify file signatures too, based on the LSM hooks
> > in  kernel_read_file_from_fd().  CONFIG_KEXEC_VERIFY_SIG should not be
> > required.
> 
> Mimi, I remember we talked somthing before about the two signature 
> verification. One can change IMA policy in initramfs userspace,
> also there are kernel cmdline param to disable IMA, so it can break the
> lockdown? Suppose kexec boot with ima disabled cmdline param and then
> kexec reboot again..

I guess I should lock down the parameter to disable IMA too.

David