Re: [PATCH v39 13/24] x86/sgx: Add SGX_IOC_ENCLAVE_ADD_PAGES

[Jarkko Sakkinen]

On Mon, Oct 19, 2020 at 02:44:19PM -0700, Dave Hansen wrote:
> On 10/19/20 2:15 PM, Sean Christopherson wrote:
> >>>> Yeah...  Don't we need to do another access_ok() check here, if we
> >>>> needed one above since we are moving away from addrp.src?
> >>> I don't think so because the page is pinned with get_user_pages().
> >> No, get_user_pages() is orthogonal.
> >>
> >> Looking at this again, you _might_ be OK since you validated addp.length
> >> against encl->size.  But, it's all very convoluted and doesn't look very
> >> organized or obviously right.
> > The easiest fix would be to have the existing access_ok() check the entire
> > range, no?  Or am I missing something obvious?
> 
> In general, I want the actual userspace access to be as close as
> possible and 1:1 with the access_ok() checks.  That way, it's blatantly
> obvious that the pointers have been checked.
> 
> *But* get_user_pages() has access_ok() checks inside of its
> implementation, which makes sense.  *But*, that begs the question of
> what the top-level one was doing in the first place.  Maybe it was just
> superfluous.
> 
> Either way, it still doesn't explain what this is doing:

I guess it is just history. Used to be one page ioctl.

> > +       ret = get_user_pages(src, 1, 0, &src_page, NULL);
> > +       if (ret < 1)
> > +               return -EFAULT;
> > +
> > +       pginfo.secs = (unsigned long)sgx_get_epc_addr(encl->secs.epc_page);
> > +       pginfo.addr = SGX_ENCL_PAGE_ADDR(encl_page);
> > +       pginfo.metadata = (unsigned long)secinfo;
> > +       pginfo.contents = (unsigned long)kmap_atomic(src_page);
> > +
> > +       ret = __eadd(&pginfo, sgx_get_epc_addr(epc_page));
> > +
> > +       kunmap_atomic((void *)pginfo.contents);
> 
> I think the point is to create a stable kernel alias address for
> 'src_page' so that any mucking with the userspace mapping doesn't screw
> up the __eadd() and any failures aren't due to reclaim or MADV_DONTNEED.
> 
> If this isn't even touching the userspace mapping, it didn't need
> access_ok() in the first place.

The whole access_ok() check is just evolutionary cruft. I will remove
it.

/Jarkko