On Mon, Mar 15, 2021 at 03:18:16PM +0200, Jarkko Sakkinen wrote: > On Mon, Mar 15, 2021 at 08:12:36PM +1300, Kai Huang wrote: > > On Sat, 13 Mar 2021 12:45:53 +0200 Jarkko Sakkinen wrote: > > > On Fri, Mar 12, 2021 at 01:21:54PM -0800, Sean Christopherson wrote: > > > > On Thu, Mar 11, 2021, Kai Huang wrote: > > > > > From: Jarkko Sakkinen <jar...@kernel.org> > > > > > > > > > > EREMOVE takes a page and removes any association between that page and > > > > > an enclave. It must be run on a page before it can be added into > > > > > another enclave. Currently, EREMOVE is run as part of pages being > > > > > freed > > > > > into the SGX page allocator. It is not expected to fail. > > > > > > > > > > KVM does not track how guest pages are used, which means that SGX > > > > > virtualization use of EREMOVE might fail. > > > > > > > > > > Break out the EREMOVE call from the SGX page allocator. This will > > > > > allow > > > > > the SGX virtualization code to use the allocator directly. (SGX/KVM > > > > > will also introduce a more permissive EREMOVE helper). > > > > > > > > > > Implement original sgx_free_epc_page() as sgx_encl_free_epc_page() to > > > > > be > > > > > more specific that it is used to free EPC page assigned to one > > > > > enclave. > > > > > Print an error message when EREMOVE fails to explicitly call out EPC > > > > > page is leaked, and requires machine reboot to get leaked pages back. > > > > > > > > > > Signed-off-by: Jarkko Sakkinen <jar...@kernel.org> > > > > > Co-developed-by: Kai Huang <kai.hu...@intel.com> > > > > > Acked-by: Jarkko Sakkinen <jar...@kernel.org> > > > > > Signed-off-by: Kai Huang <kai.hu...@intel.com> > > > > > --- > > > > > v2->v3: > > > > > > > > > > - Fixed bug during copy/paste which results in SECS page and va > > > > > pages are not > > > > > correctly freed in sgx_encl_release() (sorry for the mistake). > > > > > - Added Jarkko's Acked-by. > > > > > > > > That Acked-by should either be dropped or moved above Co-developed-by > > > > to make > > > > checkpatch happy. > > > > > > > > Reviewed-by: Sean Christopherson <sea...@google.com> > > > > > > Oops, my bad. Yup, ack should be removed. > > > > > > /Jarkko > > > > Hi Jarkko, > > > > Your reply of your concern of this patch to the cover-letter > > > > https://lore.kernel.org/lkml/yekjxu262yda8...@kernel.org/ > > > > reminds me to do more sanity check of whether removing EREMOVE in > > sgx_free_epc_page() will impact other code path or not, and I think > > sgx_encl_release() is not the only place should be changed: > > > > - sgx_encl_shrink() needs to call sgx_encl_free_epc_page(), since when this > > is > > called, the VA page can be already valid -- there are other failures can > > trigger sgx_encl_shrink(). > > You right about this, good catch. > > Shrink needs to always do EREMOVE as grow has done EPA, which changes > EPC page state. > > > - sgx_encl_add_page() should call sgx_encl_free_epc_page() in > > "err_out_free:" > > label, since the EPC page can be already valid when error happened, i.e. > > when > > EEXTEND fails. > > Yes, correct, good work! > > > Other places should be OK per my check, but I'd prefer to just replacing all > > sgx_free_epc_page() call sites in driver with sgx_encl_free_epc_page(), with > > one exception: sgx_alloc_va_page(), which calls sgx_free_epc_page() when EPA > > fails, in which case EREMOVE is not required for sure. > > I would not unless they require it. > > > Your idea, please? > > > > Btw, introducing a driver wrapper of sgx_free_epc_page() does make sense to > > me, > > because virtualization has a counterpart in sgx/virt.c too. > > It does make sense to use sgx_free_epc_page() everywhere where it's > the right thing to call and here's why. > > If there is some unrelated regression that causes EPC page not get > uninitialized when it actually should, doing extra EREMOVE could mask > those bugs. I.e. it can postpone a failure, which can make a bug harder > to backtrace. >
I.e. even though it is true that for correctly working code extra EREMOVE is nil functionality, it could change semantics for buggy code. /Jarkko
