On Mon, Dec 17, 2018 at 07:49:35PM +0200, Jarkko Sakkinen wrote: > 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 > behaviour. No, EREMOVE should never fail if the enclave is being released, i.e. all references to the enclave are gone. And failure during sgx_encl_release() means we leaked an EPC page, which warrants a WARN. The only legitimate reason __sgx_free_page() can fail in sgx_invalidate() is because a page might be in the process of being reclaimed. We could theoretically WARN on EREMOVE failure in that case, but it'd make the code a little fragile and it's not "fatal" in the sense that we get a second chance to free the page during sgx_encl_release(). And unless I missed something, using sgx_invalidate() means were' leaking all sgx_encl_page structs as well as the radix tree entries. > > 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? That makes sense.
