linux-kernel - Re: [PATCH v3 03/25] x86/sgx: Wipe out EREMOVE from sgx_free_epc

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Message-ID: <5d5eacef-b43b-529f-1425-0ec27b60e6ad@redhat.com>
Date:   Tue, 23 Mar 2021 18:06:19 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Borislav Petkov <bp@...en8.de>, Kai Huang <kai.huang@...el.com>,
        kvm@...r.kernel.org, x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, jarkko@...nel.org, luto@...nel.org,
        dave.hansen@...el.com, rick.p.edgecombe@...el.com,
        haitao.huang@...el.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com
Subject: Re: [PATCH v3 03/25] x86/sgx: Wipe out EREMOVE from
 sgx_free_epc_page()

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