Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <5789f26ca5568f05b9554053a1c6c3309d5c36e8.camel@linux.ibm.com>
Subject: Re: [PATCH 1/1] powerpc/kvm/book3s: Fixes possible 'use after
 release' of kvm
From:   Leonardo Bras <leonardo@linux.ibm.com>
To:     Paul Mackerras <paulus@ozlabs.org>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>
Date:   Thu, 28 Nov 2019 13:24:22 -0300
In-Reply-To: <20191127225747.GA2317@blackberry>
References: <20191126175212.377171-1-leonardo@linux.ibm.com>
         <20191127225747.GA2317@blackberry>
Content-Type: multipart/signed; micalg="pgp-sha256";
        protocol="application/pgp-signature"; boundary="=-PNohgKkP6BiPP+29h/le"
User-Agent: Evolution 3.34.1 (3.34.1-1.fc31) 
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--=-PNohgKkP6BiPP+29h/le
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Thu, 2019-11-28 at 09:57 +1100, Paul Mackerras wrote:
> There isn't a potential use-after-free here.  We are relying on the
> property that the release function (kvm_vm_release) cannot be called
> in parallel with this function.  The reason is that this function
> (kvm_vm_ioctl_create_spapr_tce) is handling an ioctl on a kvm VM file
> descriptor.  That means that a userspace process has the file
> descriptor still open.  The code that implements the close() system
> call makes sure that no thread is still executing inside any system
> call that is using the same file descriptor before calling the file
> descriptor's release function (in this case, kvm_vm_release).  That
> means that this kvm_put_kvm() call here cannot make the reference
> count go to zero.

That was very informative. A lot of things are clear to me now.
Thanks for explaining this Paul.=20

Best regards,
Leonardo

--=-PNohgKkP6BiPP+29h/le
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: This is a digitally signed message part
Content-Transfer-Encoding: 7bit

-----BEGIN PGP SIGNATURE-----

iQIzBAABCAAdFiEEMdeUgIzgjf6YmUyOlQYWtz9SttQFAl3f9LYACgkQlQYWtz9S
ttTuFRAAzklmvK/yrMAbKL0SscgkU2u5KsQ6td7bys4CpwCyjrFvMpPEhTscVF6l
oJ/MuPcpEikVISnJTdqpbnyRp3fyZE105GBKP1LN5aXp+1HxT4DZHggSwuQg0THh
9dce2RIjBaa+dUtLlFselG4xWBkJoUzVM1yNpvxhNLJGc52+mCmDmUeA3icT/NoY
uKVtuOBfE7/UK94AhuBUkvVoUNGMPmLof+czvZPIuVc8Vprga3cXIpjLT2lw8Stk
nKriyJO0/MVDTEU6mcqUYRfHUW2c2SAeae3AGz0HiXfPX3ar0Xl+wCd8vX+yO07S
QmkWlKnvyBQi7WSHwg54xtbPDQBxig0PwOrG2OTDlZDuWT3PfGvYy9q2C5FOABcH
xgxe4fas0u1dw/MY/JKo/DnJBq7L+aIu2faQDCRV6E/BI6s7t84nkEqALxQAmDvK
uGPEtt2L/5Y/V9h78kJG501Xfz0TESuSfa9dTlOkUTvgKz0MCogTJFVI5wgPGYS+
PK9aGMCRNzggyNprKsy+V76fvWy5LyR4L1ZfvToSVpTkd3kXV6prD2oRH2hYuVTX
+MGhuqMf56WNUug++Yc82DAHTNJAwMpAs9nOwK7xoOwIs+4t5di4PdjK1KjwFhlO
SIDljErVyer2WdJSIvW+CaUczw8qlrx4qqus8ffqI/Jnf64fZPQ=
=hQv1
-----END PGP SIGNATURE-----

--=-PNohgKkP6BiPP+29h/le--