linux-kernel - Re: [PATCH v3 1/3] ptrace: Provide ___ptrace_may_access() that can be applied on arbitrary tasks

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Date:   Tue, 4 Sep 2018 19:35:29 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        Oleg Nesterov <oleg@...hat.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v3 1/3] ptrace: Provide ___ptrace_may_access() that can
 be applied on arbitrary tasks

On Tue, 4 Sep 2018, Tim Chen wrote:

> > Current ptrace_may_access() implementation assumes that the 'source' task is
> > always the caller (current).
> > 
> > Expose ___ptrace_may_access() that can be used to apply the check on arbitrary
> > tasks.
> 
> Casey recently has proposed putting the decision making of whether to
> do IBPB in the security module.
> 
> https://lwn.net/ml/kernel-hardening/20180815235355.14908-4-casey.schaufler@intel.com/
> 
> That will have the advantage of giving the administrator a more flexibility
> of when to turn on IBPB.  The policy is very similar to what you have proposed here
> but I think the security module is a more appropriate place for the security policy.

Yeah, well, honestly, I have a bit hard time buying the "generic 
sidechannel prevention security module" idea, given how completely 
different in nature all the mitigations have been so far. I don't see that 
trying to abstract this somehow provides more clarity.

So if this should be done in LSM, it'd probably have to be written by 
someone else than me :) who actually understands how the "sidechannel LSM" 
idea works.

Thanks,

-- 
Jiri Kosina
SUSE Labs