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

Dave Hansen
2021-09-13T14:09:54Z

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().

sgx_vepc_free_page() should do the same for pages that a guest not not
clean up properly.

sgx_encl_free_epc_page() does an EREMOVE after a normal enclave has used
a page.

Those are the only three cases that I can think of. So, it sounds like
one of those is buggy, or there's another unexpected path out there.
Ultimately, I think it would be really handy if we could do this EREMOVE
implicitly and without any new ABI.