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Message-ID: <YBsbojMEeq3pCNhy@kernel.org>
Date: Wed, 3 Feb 2021 23:54:42 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: linux-sgx@...r.kernel.org, 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 Wed, Feb 03, 2021 at 07:46:48AM -0800, Dave Hansen wrote:
> 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.
I'll bake up a new patch. Generally speaking, I think why this has been so
difficult, is because of a chicken-egg-problem. The whole issue should be
sorted when a new entry is first added to the mm_list, i.e. increase the
refcount for each added entry.
/Jarkko
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