linux-kernel - Re: [intel-sgx-kernel-dev] [PATCH v7 4/8] intel_sgx: driver for Intel Software Guard Extensions

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Date:   Thu, 14 Dec 2017 15:10:06 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     "intel-sgx-kernel-dev@...ts.01.org" 
        <intel-sgx-kernel-dev@...ts.01.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Shevchenko <andy@...radead.org>
Subject: Re: [intel-sgx-kernel-dev] [PATCH v7 4/8] intel_sgx: driver for
 Intel Software Guard Extensions

On Tue, Dec 12, 2017 at 01:46:48PM -0800, Sean Christopherson wrote:
> So it looks like you avoid the described case by moving B to the head of
> the list in sgx_eldu.  The bug I am seeing is still straightforward to
> theorize:
> 
>     1. Three VA pages.  List = A->B->C
>     2. Fill A and B, use one entry in C.  List = C->B->A
>     3. ELDU, freeing a slot in B.  List = B->C->A
>     4. EWB, consuming the last slot in B.  List = B->C->A
>     5. ELDU, freeing a slot in A.  List = A->B->C
>     6. EWB, consuming the last slot in A.  List = A->B->C
>     7. ELDU, but both A and B are full
>     8. Explode

I see. It is easy to fix by moving back to of the list immediately after
last allocation. Thanks for pointing this out.

/Jarkko