On 21/09/21 21:44, Jarkko Sakkinen wrote:
"On bare-metal SGX, start of a power cycle zeros all of its reserved
memory. This happens after every reboot, but in addition to that
happens after waking up from any of the sleep states."
I can speculate and imagine where this might useful, but no matter
how trivial or complex it is, this patch needs to nail a concrete
usage example. I'd presume you know well the exact changes needed for
QEMU, so from that knowledge it should be easy to write the
motivational part.
Assuming that it's obvious that QEMU knows how to reset a machine (which
includes writes to the ACPI reset register, or wakeup from sleep
states), the question of "why does userspace reuse vEPC" should be
answered by this paragraph:
"One way to do this is to simply close and reopen the /dev/sgx_vepc file
descriptor and re-mmap the virtual EPC. However, this is problematic
because it prevents sandboxing the userspace (for example forbidding
open() after the guest starts, or running in a mount namespace that
does not have access to /dev; both are doable with pre-opened file
descriptors and/or SCM_RIGHTS file descriptor passing)."
Even to a Linux guest, since EPC should stil be represented in the
state that matches the hardware. It'd be essentially a corrupted
state, even if there was measures to resist this. Windows guests
failing is essentially a side-effect of an issue, not an issue in the
Windows guests.
Right, Linux is more liberal than it needs to be and ksgxd does the
EREMOVE itself at the beginning (__sgx_sanitize_pages). Windows has
stronger expectations of what can and cannot happen before it boots,
which are entirely justified.
Paolo
