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

[Jarkko Sakkinen]

On Sun, Dec 05, 2021 at 12:25:59AM +0200, Jarkko Sakkinen wrote:
> 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.

3. Isn't this an API/ABI break?

/Jarkko