From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver Date: Mon, 17 Dec 2018 10:09:57 -0800 Message-ID: <20181217180957.GC12491@linux.intel.com> References: <20181128192228.GC9023@linux.intel.com> <20181210104908.GA23132@wind.enjellic.com> <20181212180036.GC6333@linux.intel.com> <20181214235917.GA14049@wind.enjellic.com> <20181215000627.GA5799@linux.intel.com> <20181217132859.GA31936@linux.intel.com> <20181217133928.GA32706@linux.intel.com> <20181217140811.GA4601@linux.intel.com> <20181217173106.GB12491@linux.intel.com> <20181217174935.GA12617@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20181217174935.GA12617@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Jarkko Sakkinen Cc: "Dr. Greg" , Andy Lutomirski , Andy Lutomirski , X86 ML , Platform Driver , linux-sgx@vger.kernel.org, Dave Hansen , nhorman@redhat.com, npmccallum@redhat.com, "Ayoun, Serge" , shay.katz-zamir@intel.com, haitao.huang@linux.intel.com, Andy Shevchenko , Thomas Gleixner , "Svahn, Kai" , mark.shanahan@intel.com, Suresh Siddha , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Darren Hart , Andy Shevchenko LKML List-Id: platform-driver-x86.vger.kernel.org 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.