[Pal/Linux-SGX] Sanitize VMID

[boryspoplawski]

Description of the problem

Graphene uses host process PID as a VMID (Graphenes process internal id). Malicious host could put an unexpected value there e.g. to create collisisons.
We should sanitize the value or, more likely, just fully randomize it (would 64bit be enough?). If anybody knows a better solution, please post it here.

Reference:
https://github.com/oscarlab/graphene/blob/4c850181e2efa6754b7da4960fc41f416824e3b2/Pal/src/host/Linux-SGX/db_main.c#L293
Soon the time above will be removed leaving only pid.

[boryspoplawski]

I think we can just use sequential values as there should be no need for randomization. The malicious host could know that value and it should not pose any security risks.