linux-kernel - Re: [PATCH v5 3/8] ima: based on policy require signed kexec kernel images

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Date:   Tue, 03 Jul 2018 09:07:39 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     J Freyensee <why2jjj.linux@...il.com>,
        linux-integrity@...r.kernel.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org, Andres Rodriguez <andresx7@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v5 3/8] ima: based on policy require signed kexec kernel
 images

On Mon, 2018-07-02 at 11:31 -0700, J Freyensee wrote:
> 
> On 7/2/18 7:37 AM, Mimi Zohar wrote:
> > The original kexec_load syscall can not verify file signatures, nor can
> > the kexec image be measured.  Based on policy, deny the kexec_load
> > syscall.
> 
> 
> Curiosity question: I thought kexec_load() syscall was used to load a 
> crashdump?

kexec is used to collect the memory used to analyze the crash dump.

> If this is true, how would this work if kexec_load() is 
> being denied?  I don't think I'd want to be hindered in cases where I'm 
> trying to diagnose a crash.

For trusted & secure boot, we need a full measurement list and
signature chain of trust rooted in HW.  Permitting kexec_load would
break these chains of trust.

Permitting/denying kexec_load is based on a runtime IMA policy.  Patch
6/8 "ima: add build time policy", in this patch set, introduces the
concept of a build time policy.  With these patches, you could
configure your kernel and/or load an IMA policy permitting kexec_load.

Mimi