Re: [PATCH 03/25] x86/sgx: Support VMA permissions exceeding enclave permissions

[Jarkko Sakkinen]

On Wed, Dec 01, 2021 at 11:23:01AM -0800, Reinette Chatre wrote:
> === Summary ===
> 
> An SGX VMA can only be created if its permissions are the same or
> weaker than the Enclave Page Cache Map (EPCM) permissions. After VMA
> creation this rule continues to be enforced by the page fault handler.
> 
> With SGX2 the EPCM permissions of a page can change after VMA
> creation resulting in the VMA exceeding the EPCM permissions and the
> page fault handler incorrectly blocking access.
> 
> Enable the VMA's pages to remain accessible while ensuring that
> the page table entries are installed to match the EPCM permissions
> without exceeding the VMA perms issions.

I don't understand what the short summary means in English, and the
commit message is way too bloated to make any conclusions. It really
needs a rewrite.

These were the questions I could not find answer for:

1. Why it would be by any means safe to remove a permission check?
2. Why not re-issuing mmap()'s is unfeasible? I.e. close existing
   VMA's and mmap() new ones.

/Jarkko