Re: [RFC PATCH 3/9] x86/sgx: Allow userspace to add multiple pages in single ioctl()

[Andy Lutomirski]

On Mon, Jun 3, 2019 at 1:39 PM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> On Mon, Jun 03, 2019 at 01:08:04PM -0700, Sean Christopherson wrote:
> > On Sun, Jun 02, 2019 at 11:26:09PM -0700, Xing, Cedric wrote:
> > > > From: Christopherson, Sean J
> > > > Sent: Friday, May 31, 2019 4:32 PM
> > > >
> > > > +/**
> > > > + * sgx_ioc_enclave_add_pages - handler for %SGX_IOC_ENCLAVE_ADD_PAGES
> > > > + *
> > > > + * @filep:       open file to /dev/sgx
> > > > + * @cmd: the command value
> > > > + * @arg: pointer to an &sgx_enclave_add_page instance
> > > > + *
> > > > + * Add a range of pages to an uninitialized enclave (EADD), and
> > > > +optionally
> > > > + * extend the enclave's measurement with the contents of the page (EEXTEND).
> > > > + * The range of pages must be virtually contiguous.  The SECINFO and
> > > > + * measurement maskare applied to all pages, i.e. pages with different
> > > > + * properties must be added in separate calls.
> > > > + *
> > > > + * EADD and EEXTEND are done asynchronously via worker threads.  A
> > > > +successful
> > > > + * sgx_ioc_enclave_add_page() only indicates the pages have been added
> > > > +to the
> > > > + * work queue, it does not guarantee adding the pages to the enclave
> > > > +will
> > > > + * succeed.
> > > > + *
> > > > + * Return:
> > > > + *   0 on success,
> > > > + *   -errno otherwise
> > > > + */
> > > > +static long sgx_ioc_enclave_add_pages(struct file *filep, unsigned int cmd,
> > > > +                               unsigned long arg)
> > > > +{
> > > > + struct sgx_enclave_add_pages *addp = (void *)arg;
> > > > + struct sgx_encl *encl = filep->private_data;
> > > > + struct sgx_secinfo secinfo;
> > > > + unsigned int i;
> > > > + int ret;
> > > > +
> > > > + if (copy_from_user(&secinfo, (void __user *)addp->secinfo,
> > > > +                    sizeof(secinfo)))
> > > > +         return -EFAULT;
> > > > +
> > > > + for (i = 0, ret = 0; i < addp->nr_pages && !ret; i++) {
> > > > +         if (signal_pending(current))
> > > > +                 return -ERESTARTSYS;
> > >
> > > If interrupted, how would user mode code know how many pages have been EADD'ed?
> >
> > Hmm, updating nr_pages would be fairly simple and shouldn't confuse
> > userspace, e.g. as opposed to overloading the return value.
>
> Or maybe update @addr and @src as well?  That would allow userspace to
> re-invoke the ioctl() without having to modify the struct.

If you're going to use -ERESTARTSYS, that's the way to go.  -EINTR
would be an alternative.  A benefit of -ERESTARTSYS is that, with
-EINTR, it wouldn't be that surprising for user code to simply fail to
handle it.