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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id d14sm2013598qtr.62.2020.10.07.10.39.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Oct 2020 10:39:11 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kQDPD-00112O-7o; Wed, 07 Oct 2020 14:39:11 -0300 Date: Wed, 7 Oct 2020 14:39:11 -0300 From: Jason Gunthorpe To: Daniel Vetter Cc: DRI Development , LKML , kvm@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, linux-s390@vger.kernel.org, Daniel Vetter , Kees Cook , Dan Williams , Andrew Morton , John Hubbard , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Jan Kara , Alex Williamson , Cornelia Huck Subject: Re: [PATCH 13/13] vfio/type1: Mark follow_pfn as unsafe Message-ID: <20201007173911.GX5177@ziepe.ca> References: <20201007164426.1812530-1-daniel.vetter@ffwll.ch> <20201007164426.1812530-14-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201007164426.1812530-14-daniel.vetter@ffwll.ch> Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Oct 07, 2020 at 06:44:26PM +0200, Daniel Vetter wrote: > The code seems to stuff these pfns into iommu pts (or something like > that, I didn't follow), but there's no mmu_notifier to ensure that > access is synchronized with pte updates. >=20 > Hence mark these as unsafe. This means that with > CONFIG_STRICT_FOLLOW_PFN, these will be rejected. >=20 > Real fix is to wire up an mmu_notifier ... somehow. Probably means any > invalidate is a fatal fault for this vfio device, but then this > shouldn't ever happen if userspace is reasonable. >=20 > Signed-off-by: Daniel Vetter > Cc: Jason Gunthorpe > Cc: Kees Cook > Cc: Dan Williams > Cc: Andrew Morton > Cc: John Hubbard > Cc: J=C3=A9r=C3=B4me Glisse > Cc: Jan Kara > Cc: Dan Williams > Cc: linux-mm@kvack.org > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-samsung-soc@vger.kernel.org > Cc: linux-media@vger.kernel.org > Cc: Alex Williamson > Cc: Cornelia Huck > Cc: kvm@vger.kernel.org > --- > drivers/vfio/vfio_iommu_type1.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) >=20 > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_= type1.c > index 5fbf0c1f7433..a4d53f3d0a35 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -421,7 +421,7 @@ static int follow_fault_pfn(struct vm_area_struct *= vma, struct mm_struct *mm, > { > int ret; > =20 > - ret =3D follow_pfn(vma, vaddr, pfn); > + ret =3D unsafe_follow_pfn(vma, vaddr, pfn); > if (ret) { > bool unlocked =3D false; > =20 > @@ -435,7 +435,7 @@ static int follow_fault_pfn(struct vm_area_struct *= vma, struct mm_struct *mm, > if (ret) > return ret; > =20 > - ret =3D follow_pfn(vma, vaddr, pfn); > + ret =3D unsafe_follow_pfn(vma, vaddr, pfn); > } This is actually being commonly used, so it needs fixing. When I talked to Alex about this last we had worked out a patch series that adds a test on vm_ops that the vma came from vfio in the first place. The VMA's created by VFIO are 'safe' as the PTEs are never changed= . Jason