Re: [PATCH 1/2] x86: sgx_vepc: extract sgx_vepc_remove_page

Jarkko Sakkinen
2021-09-13T21:00:53Z

On Mon, 2021-09-13 at 16:24 +0200, Paolo Bonzini wrote:
> On 13/09/21 16:05, Dave Hansen wrote:
> > On 9/13/21 6:11 AM, Paolo Bonzini wrote:
> > > Windows expects all pages to be in uninitialized state on startup.
> > > In order to implement this, we will need a ioctl that performs
> > > EREMOVE on all pages mapped by a /dev/sgx_vepc file descriptor:
> > > other possibilities, such as closing and reopening the device,
> > > are racy.
> >
> > Hi Paolo,
> >
> > How does this end up happening in the first place?
> >
> > All enclave pages should start out on 'sgx_dirty_page_list' and
> > ksgxd sanitizes them with EREMOVE before making them available. That
> > should cover EREMOVE after reboots while SGX pages are initialized,
> > including kexec().
>
> By "Windows startup" I mean even after guest reboot. Because another
> process could sneak in and steal your EPC pages between a close() and an
> open(), I'd like to have a way to EREMOVE the pages while keeping them
> assigned to the specific vEPC instance, i.e. *without* going through
> sgx_vepc_free_page().

Isn't "other process in and steal your EPC pages" more like sysadmin
problem, rather than software?

I'm lacking of understanding what would be the collateral damage in
the end.

/Jarkko