Re: [PATCH V2 16/32] x86/sgx: Support restricting of enclave page permissions

[Jarkko Sakkinen]

On Thu, Mar 10, 2022 at 07:43:42AM +0200, Jarkko Sakkinen wrote:
> On Thu, Mar 03, 2022 at 01:44:14PM -0800, Dave Hansen wrote:
> > On 3/3/22 13:23, Reinette Chatre wrote:
> > > Unfortunately MAP_POPULATE is not supported by SGX VMAs because of their
> > > VM_IO and VM_PFNMAP flags. When VMAs with such flags obtain this capability
> > > then I believe that SGX would benefit.
> > 
> > Some Intel folks asked for this quite a while ago.  I think it's
> > entirely doable: add a new vm_ops->populate() function that will allow
> > ignoring VM_IO|VM_PFNMAP if present.
> > 
> > Or, if nobody wants to waste all of the vm_ops space, just add an
> > arch_vma_populate() or something which can call over into SGX.
> > 
> > I'll happily review the patches if anyone can put such a beast together.
> 
> Everyone would be better off, if EAUG's were done unconditionally for
> mmap() after initialization. Nice property is that this needs no core mm
> changes.
> 
> The resource saving argument is at least a bit weak because you might use
> EMODPR for the address range anyway. So you end up doing things just
> slower. And to have good confidentiality, you actually probably want to
> clear also dynamically added pages with EACCEPTCOPY (and zero page) when
> you take them into use.
> 
> I find it also a bit worrying that enclave has direct access to allocate
> kernel resources and trigger ring-0 opcode. I don't like that part at
> all. syscall/ioctl sets the correct barrier, as the host side should be
> and is the resource manager, not the enclave.

Actually, this should be ABI compatible too. I'd expect all kselftests
continue work as they are.

BR, Jarkko