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

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Date:   Wed, 5 Sep 2018 10:00:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        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, Sep 04, 2018 at 07:35:29PM +0200, Jiri Kosina wrote:
> 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.

Yeah, I'm not convinced on LSM either. Lets just do these here patches
first and then Casey can try and convince us later.