Re: [PATCH v2 2/2] x86: sgx_vepc: implement SGX_IOC_VEPC_REMOVE ioctl

Dave Hansen
2021-10-14T22:15:01Z

On 10/12/21 3:57 AM, Paolo Bonzini wrote:
> For bare-metal SGX on real hardware, the hardware provides guarantees
> SGX state at reboot. For instance, all pages start out uninitialized.
> The vepc driver provides a similar guarantee today for freshly-opened
> vepc instances, but guests such as Windows expect all pages to be in
> uninitialized state on startup, including after every guest reboot.
>
> Some userspace implementations of virtual SGX would rather avoid having
> to close and reopen the /dev/sgx_vepc file descriptor and re-mmap the
> virtual EPC. For example, they could sandbox themselves after the guest
> starts and forbid further calls to open(), in order to mitigate exploits
> from untrusted guests.
>
> Therefore, add a ioctl that does this with EREMOVE. Userspace can
> invoke the ioctl to bring its vEPC pages back to uninitialized state.
> There is a possibility that some pages fail to be removed if they are
> SECS pages, and the child and SECS pages could be in separate vEPC
> regions. Therefore, the ioctl returns the number of EREMOVE failures,
> telling userspace to try the ioctl again after it's done with all
> vEPC regions. A more verbose description of the correct usage and
> the possible error conditions is documented in sgx.rst.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

The new approach and revised changelogs look fine to me:

Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>

Like Jarkko mentioned, it would be _nice_ to have some self-contained
selftests around this. Would it be a pain to rig something up in
selftests/kvm that at least trivially poked at /dev/sgx_vepc?