On Tue, 14 Feb 2023 14:54:53 -0600, Huang, Kai <kai.huang@xxxxxxxxx> wrote:
On Tue, 2023-02-14 at 13:18 -0600, Haitao Huang wrote:
Hi Kai
On Tue, 14 Feb 2023 03:47:24 -0600, Huang, Kai <kai.huang@xxxxxxxxx>
wrote:
> On Fri, 2023-01-27 at 20:55 -0800, Haitao Huang wrote:
> > @@ -97,10 +99,81 @@ static int sgx_mmap(struct file *file, struct
> > vm_area_struct *vma)
> > vma->vm_ops = &sgx_vm_ops;
> > vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
> > vma->vm_private_data = encl;
> > + vma->vm_pgoff = PFN_DOWN(vma->vm_start - encl->base);
> > return 0;
> > }
>
> Perhaps I am missing something, but above change looks weird.
> Conceptually, it doesn't/shouldn't belong to this series, which
> essentially
> preallocates and does EAUG EPC pages for a (or part of) given enclave.
> The EAUG
> logic should already be working for the normal fault path, which means
> the code
> change above either: 1) has been done at other place; 2) isn't needed.
>
> I have kinda forgotten the userspace sequence to create an enclave.
If
> I recall
> correctly, you do below to create an enclave:
>
> 1) encl_fd = open("/dev/sgx_enclave");
> 2) encl_addr = mmap(encl_fd, encl_size, 0 /* pgoff */);
> 3) IOCTL(ECREATE, encl_addr, encl_size);
>
> Would the above code change break the "mmap()" in above step 2?
>
No, vm_pgoff was not used previously for enclave VMAs. I had to add this
because the offset passed to sgx_fadvise is relative to file base and
calculated in mm/madvise.c like this:
offset = (loff_t)(start - vma->vm_start)
+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
But shouldn't 'offset is relative to the file base' be conceptually
correct from
the fadvice()'s point of view?
I think you should do:
encl_offset = offset + encl->base;
inside sgx_fadvice()?
If we don't set vma->vm_pgoff (default to zero), then offset will be
calculated as (start - vma->vm_start). Then the above calculation is wrong
if we have multiple VMAs for the same enclave, which is usually the case.
I had a comment in first version but removed it based on Jarkko's
suggestion here:
https://lore.kernel.org/all/Y2B0jBsG6HE4KVk7@xxxxxxxxxx/
The original comments probably seemed redundant to the definitions of
the
vm_pgoff field and the fadvise interface. But let me know if we need
add a
more helpful version of comments or any suggestion on the comments.
I still think this code change is wrong.
For instance, IIUC, it at least breaks the case where enclave hasn't been
created/initialized, where encl->base == 0 (although normal code path
doesn't
use vm_pgoff, conceptually it's still wrong IIUC).
Maybe I am missing something?
The fadvise interface is only usable for an initialized enclave,
sgx_fadvise will return error otherwise. Conceptually I view enclave base
as "file base", it's just that we don't ever need handle the zero case
caused by uninitialized enclave (kind of like a file never mapped). If an
initialized enclave happens to have zero base, it would also work.
Thanks
Haitao
