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

From: Jarkko Sakkinen
Date: Mon Dec 17 2018 - 12:49:48 EST

On Mon, Dec 17, 2018 at 09:31:06AM -0800, Sean Christopherson wrote:
> This doesn't work as-is. sgx_encl_release() needs to use sgx_free_page()
> and not __sgx_free_page() so that we get a WARN() if the page can't be
> freed. sgx_invalidate() needs to use __sgx_free_page() as freeing a page
> can fail due to running concurrently with reclaim. I'll play around with
> the code a bit, there's probably a fairly clean way to share code between
> the two flows.

Hmm... but why issue a warning in that case? It should be legit

> sgx_encl_release_worker() calls do_unmap() without checking the validity
> of the page tables[1]. As is, the code doesn't even guarantee mm_struct
> itself is valid.
> The easiest fix I can think of is to add a SGX_ENCL_MM_RELEASED flag
> that is set along with SGX_ENCL_DEAD in sgx_mmu_notifier_release(), and
> only call do_unmap() if SGX_ENCL_MM_RELEASED is false. Note that this
> means we cant unregister the mmu_notifier until after do_unmap(), but
> that's true no matter what since we're relying on the mmu_notifier to
> hold a reference to mm_struct. Patch attached.

OK, the fix change makes sense but I'm thinking that would it be a
better idea just to set mm NULL and check that instead?