On Mon, Oct 05, 2020 at 02:48:07PM +0300, Jarkko Sakkinen wrote:
> On Mon, Oct 05, 2020 at 12:11:39PM +0100, Matthew Wilcox wrote:
> > On Mon, Oct 05, 2020 at 06:17:59AM +0300, Jarkko Sakkinen wrote:
> > > @@ -317,10 +318,31 @@ int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start,
> > > if (current->personality & READ_IMPLIES_EXEC)
> > > return -EACCES;
> > >
> > > - xas_for_each(&xas, page, idx_end)
> > > + /*
> > > + * No need to hold encl->lock:
> > > + * 1. None of the page->* get written.
> > > + * 2. page->vm_max_prot_bits is set in sgx_encl_page_alloc(). This
> > > + * is before calling xa_insert(). After that it is never modified.
> > > + */
> > > + xas_lock(&xas);
> > > + xas_for_each(&xas, page, idx_end) {
> > > + if (++count % XA_CHECK_SCHED)
> > > + continue;
> >
> > This really doesn't do what you think it does.
> >
> > int ret = 0;
> > int count = 0;
> >
> > xas_lock(&xas);
> > while (xas.index < idx_end) {
> > struct sgx_page *page = xas_next(&xas);
> >
> > if (!page || (~page->vm_max_prot_bits & vm_prot_bits)) {
> > ret = -EACCESS;
> > break;
> > }
> >
> > if (++count % XA_CHECK_SCHED)
> > continue;
> > xas_pause(&xas);
> > xas_unlock(&xas);
> > cond_resched();
> > xas_lock(&xas);
> > }
> > xas_unlock(&xas);
> >
> > return ret;
>
> No mine certainly does not, it locks up the system if the loop succeeds
> (i.e. does not return -EACCESS) :-) Unfortunately had by mistake the v1
> patch (xa_load()) in the kernel that I used to test.
... and not having xas_unlock() in the end was not intentional.
/Jarkko
