linux-kernel - Re: [PATCH v4 0/8] kexec/firmware: support system wide policy requiring signatures

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Date:   Mon, 4 Jun 2018 15:03:01 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <james.l.morris@...cle.com>,
        Paul Moore <paul@...l-moore.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kexec Mailing List <kexec@...ts.infradead.org>,
        Andres Rodriguez <andresx7@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH v4 0/8] kexec/firmware: support system wide policy
 requiring signatures

On Mon, Jun 4, 2018 at 7:03 AM, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> On Tue, 2018-05-29 at 14:01 -0400, Mimi Zohar wrote:
>> Instead of adding the security_kernel_read_file LSM hook - or defining a
>> wrapper for security_kernel_read_file LSM hook and adding it, or
>> renaming the existing hook to security_kernel_read_data() and adding it
>> - in places where the kernel isn't reading a file, this version of the
>> patch set defines a new LSM hook named security_kernel_load_data().
>>
>> The new LSM hook does not replace the existing security_kernel_read_file
>> LSM hook, which is still needed, but defines a new LSM hook allowing
>> LSMs and IMA-appraisal the opportunity to fail loading userspace
>> provided file/data.
>>
>> The only difference between the two LSM hooks is the LSM hook name and a
>> file descriptor.  Whether this is cause enough for requiring a new LSM
>> hook, is left to the security community.
>
> Paul does not have a preference as to adding a new LSM hook or calling
> the existing hook.  Either way is fine, as long as both the new and
> existing hooks call the existing function.
>
> Casey didn't like the idea of a wrapper.
> James suggested renaming the LSM hook.
>
> The maintainers for the callers of the LSM hook prefer a meaningful
> LSM hook name.  The "null" argument is not as much of a concern.  Only
> Eric seems to be asking for a separate, new LSM hook, without the
> "null" argument.
>
> Unless someone really objects, to accommodate Eric we'll define a new
> LSM hook named security_kernel_load_data.  Eric, are you planning on
> Ack'ing patches 1 & 2?

I'm sorry I'm late to review this series. Reading through what you
have, it seems like the existing hook is fine. If the name has
slipped, we can rename it, but I think adding another hook for the
same logical action (loading something into the kernel) is confusing.

It seems that only patches needed are 2 & 4 (new hook callsites), 5, 6
& 7 (IMA coverage and policy). 1 and 8 seem needless to me. If the
objection is that isn't use on non-file objects, sure, rename it. But
I don't see a _logical_ difference between the proposed and existing
callsites. enum kernel_read_file_id covers the "type" already....

-Kees

-- 
Kees Cook
Pixel Security