Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

[Sean Christopherson]

On Tue, Dec 18, 2018 at 03:13:11PM +0200, Jarkko Sakkinen wrote:
> On Mon, Dec 17, 2018 at 10:21:49PM +0200, Jarkko Sakkinen wrote:
> > On Mon, Dec 17, 2018 at 09:33:22PM +0200, Jarkko Sakkinen wrote:
> > > On Mon, Dec 17, 2018 at 10:48:58AM -0800, Sean Christopherson wrote:
> > > > On Mon, Dec 17, 2018 at 08:43:33PM +0200, Jarkko Sakkinen wrote:
> > > > > On Mon, Dec 17, 2018 at 10:36:13AM -0800, Sean Christopherson wrote:
> > > > > > I'm pretty sure doing mmget() would result in circular dependencies and
> > > > > > a zombie enclave.  In the do_exit() case where a task is abruptly killed:
> > > > > >  
> > > > > >   - __mmput() is never called because the enclave holds a ref
> > > > > >   - sgx_encl_release() is never be called because its VMAs hold refs
> > > > > >   - sgx_vma_close() is never called because __mmput()->exit_mmap() is
> > > > > >     blocked and the process itself is dead, i.e. won't unmap anything.
> > > > > 
> > > > > Right, it does, you are absolutely right. Tried it and removed the
> > > > > commit already.
> > > > > 
> > > > > Well, what we came up from your suggestion i.e. setting mm to NULL
> > > > > and checking that is very subtle change and does not have any such
> > > > > circular dependencies. We'll go with that.
> > > > 
> > > > We can't set mm to NULL as we need it to unregister the notifier, and
> > > > I'm fairly certain attempting to unregister in the release callback
> > > > will deadlock.
> > > 
> > > Noticed that too. mmu_notifier_unregister() requires a valid mm.
> > 
> > Both branches updated...
> 
> I'm not still seeing why you would want to call sgx_free_page() from
> sgx_invalidate(). Kind of resistant to adding extra logging just for
> checking for programming errors. What I would do if I had to debug
> there a leak would be simply put kretprobe on __sgx_free_page().

The WARN is needed to detect the leak in the first place.  And leaking
pages because EREMOVE fails usually means there's a serious bug.