Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
> On Thu, Dec 07, 2017 at 02:46:39PM +0000, Christopherson, Sean J wrote:
> > > + for (i = 0; i < 2; i++) {
> > > + va_page = list_first_entry(&encl->va_pages,
> > > + struct sgx_va_page, list);
> > > + va_offset = sgx_alloc_va_slot(va_page);
> > > + if (va_offset < PAGE_SIZE)
> > > + break;
> > > +
> > > + list_move_tail(&va_page->list, &encl->va_pages);
> > > + }
> >
> > This is broken, there is no guarantee that the next VA page will have
> > a free slot. You have to walk over all VA pages to guarantee a slot
> > is found, e.g. this caused EWB and ELDU errors.
>
> I did run some extensive stress tests on this and did not experience any
> issues. Full VA pages are always put to the end. Please point me to the
> test where this breaks so that I can fix the issue if it persists.
Three VA pages in the enclave: A, B and C. Evict all pages in the
enclave, i.e. consume all slots in A, B and C. The list can be in
any order at this point, but for the sake of argument let's say the
order is C->A->B, i.e. C was originally the last VA page in the list.
Fault in page X, whose VA is in B. Evict X. This code looks at C
and A, and finds no available slot, but continues with VA page A and
a va_offset of PAGE_SIZE.
