linux-kernel - Re: [PATCH v5] x86/sgx: Fix use-after-free in sgx_mmu_notifier

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Date:   Wed, 3 Feb 2021 07:46:48 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, linux-sgx@...r.kernel.org
Cc:     stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Jethro Beekman <jethro@...tanix.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] x86/sgx: Fix use-after-free in
 sgx_mmu_notifier_release()

On 1/30/21 11:20 AM, Jarkko Sakkinen wrote:
...
> Example scenario would such that all removals "side-channel" through
> the notifier callback. Then mmu_notifier_unregister() gets called
> exactly zero times. No MMU notifier srcu sync would be then happening.
> 
> NOTE: There's bunch of other examples, I'm just giving one.

Could you flesh this out a bit?  I don't quite understand the scenario
from what you describe above.

In any case, I'm open to other implementations that fix the race we know
about.  If you think you have a better fix, I'm happy to review it and
make sure it closes the other race.