Re: [PATCH v3 03/25] x86/sgx: Wipe out EREMOVE from sgx_free_epc_page()

From: Paolo Bonzini
Date: Tue Mar 23 2021 - 13:07:11 EST


On 23/03/21 18:02, Sean Christopherson wrote:
That's important, but it's even more important *to developers* that the
commit message spells out why this would be a kernel bug more often than
not. I for one do not understand it, and I suspect I'm not alone.

Maybe (optimistically) once we see that explanation we decide that the
documentation is not important. Sean, Kai, can you explain it?

Thought of a good analogy that can be used for the changelog and/or docs:

This is effectively a kernel use-after-free of EPC, and due to the way SGX works,
the bug is detected at freeing. Rather than add the page back to the pool of
available EPC, the kernel intentionally leaks the page to avoid additional
errors in the future.

Does that help?

Very much, and for me this also settles the question of documentation. Borislav or Kai, can you add it to the commit message?

Paolo