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

[Peter Zijlstra <peterz@infradead.org>]

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.