> -----Original Message----- > From: Jarkko Sakkinen <jarkko@xxxxxxxxxx> > Sent: Sunday, April 3, 2022 6:21 PM > To: Zhang, Cathy <cathy.zhang@xxxxxxxxx> > Cc: linux-sgx@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx; Chatre, Reinette > <reinette.chatre@xxxxxxxxx>; Hansen, Dave <dave.hansen@xxxxxxxxx>; Raj, > Ashok <ashok.raj@xxxxxxxxx> > Subject: Re: [RFC PATCH v3 06/10] x86/sgx: Forced EPC page zapping for > EUPDATESVN > > On Fri, Apr 01, 2022 at 10:24:05PM +0800, Cathy Zhang wrote: > > Before an EUPDATESVN instruction can be successful, all enclave pages > > (EPC) must be marked as unused in the SGX hardware metadata (EPCM). > > > > A page becomes unused when an issued EREMOVE instruction succeeds. > > To prepare for EUPDATESVN, loop over all SGX pages and attempt to > > EREMOVE them. This is fatal to running enclaves and destroys all > > enclave state and memory contents. This destruction is by design and > > mitigates any compromise of enclaves or the SGX hardware itself which > > occurred before the microcode update. > > > > An EREMOVE operation on a page may fail for a few reasons. Each has > > its own mitigations. > > > > First, EREMOVE will fail if an enclave that uses the page is > > executing. Send an IPI to all CPUs that might be running the enclave > > to force it out of the enclave long enough to EREMOVE the page. Other > > CPUs might enter the enclave in the meantime, so this is not a > > rock-solid guarantee. > > > > Second, EREMOVE can fail on special SGX metadata pages, such as SECS > > and VA. EREMOVE will work on them only after the normal SGX > > Ignoring concurrency rules that apply to any type of EPC page, VA page can > be removed at any point of time, i.e. the first sentence in this paragraph is > not factually true. Yes, the SGX metadata pages failed to be EREMOVEd and be tracked for a later retry is SECS pages. Removed "VA" from the sentence Jarkko mentioned, Thanks for pointing out! > > BR, Jarkko
