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Message-ID: <CAG8rG2w6z=P=jc1n+Ay9-iBOKSFXsfdfmuyZeEJWKJM9kSdVMA@mail.gmail.com>
Date: Tue, 21 Oct 2014 16:41:51 +0200
From: Antonios Motakis <a.motakis@...tualopensystems.com>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: kvm-arm <kvmarm@...ts.cs.columbia.edu>,
Linux IOMMU <iommu@...ts.linux-foundation.org>,
Will Deacon <will.deacon@....com>,
VirtualOpenSystems Technical Team <tech@...tualopensystems.com>,
Christoffer Dall <christoffer.dall@...aro.org>,
Eric Auger <eric.auger@...aro.org>,
Kim Phillips <kim.phillips@...escale.com>,
Marc Zyngier <marc.zyngier@....com>,
"open list:VFIO DRIVER" <kvm@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] vfio/iommu_type1: implement the VFIO_DMA_MAP_FLAG_NOEXEC
flag
On Tue, Oct 21, 2014 at 4:37 PM, Alex Williamson
<alex.williamson@...hat.com> wrote:
> On Tue, 2014-10-21 at 14:40 +0200, Antonios Motakis wrote:
>> On Mon, Oct 20, 2014 at 11:13 PM, Alex Williamson
>> <alex.williamson@...hat.com> wrote:
>> > On Mon, 2014-10-13 at 15:09 +0200, Antonios Motakis wrote:
>> >> Some IOMMU drivers, such as the ARM SMMU driver, make available the
>> >> IOMMU_NOEXEC flag, to set the page tables for a device as XN (execute never).
>> >> This affects devices such as the ARM PL330 DMA Controller, which respects
>> >> this flag and will refuse to fetch DMA instructions from memory where the
>> >> XN flag has been set.
>> >>
>> >> The flag can be used only if all IOMMU domains behind the container support
>> >> the IOMMU_NOEXEC flag. Also, if any mappings are created with the flag, any
>> >> new domains with devices will have to support it as well.
>> >>
>> >> Signed-off-by: Antonios Motakis <a.motakis@...tualopensystems.com>
>> >> ---
>> >> drivers/vfio/vfio_iommu_type1.c | 25 ++++++++++++++++++++++++-
>> >> 1 file changed, 24 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> >> index 8b4202a..e225e8f 100644
>> >> --- a/drivers/vfio/vfio_iommu_type1.c
>> >> +++ b/drivers/vfio/vfio_iommu_type1.c
>> >> @@ -569,6 +569,12 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
>> >> if (map->flags & VFIO_DMA_MAP_FLAG_READ)
>> >> prot |= IOMMU_READ;
>> >>
>> >> + if (map->flags & VFIO_DMA_MAP_FLAG_NOEXEC) {
>> >> + if (!vfio_domains_have_iommu_cap(iommu, IOMMU_CAP_NOEXEC))
>> >> + return -EINVAL;
>> >> + prot |= IOMMU_NOEXEC;
>> >> + }
>> >> +
>> >> if (!prot || !size || (size | iova | vaddr) & mask)
>> >> return -EINVAL;
>> >
>> > I think this test needs to move above adding the NOEXEC flag, otherwise
>> > we now allow mappings without read or write, which is an ABI change.
>> >
>>
>> Ack.
>>
>> >>
>> >> @@ -662,6 +668,14 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
>> >> dma = rb_entry(n, struct vfio_dma, node);
>> >> iova = dma->iova;
>> >>
>> >> + /*
>> >> + * if any of the mappings to be replayed has the NOEXEC flag
>> >> + * set, then the new iommu domain must support it
>> >> + */
>> >> + if ((dma->prot | IOMMU_NOEXEC) &&
>> >
>> > I think you mean
>> >
>> > & IOMMU_NOEXEC
>>
>> Ack.
>>
>> >
>> >> + !(domain->caps & IOMMU_CAP_NOEXEC))
>> >> + return -EINVAL;
>> >> +
>> >
>> > In patch 2/5 you stated:
>> >
>> > The IOMMU_NOEXEC flag needs to be available for all the IOMMUs
>> > of the container used.
>> >
>> > But here you'll create heterogeneous containers so long as there are no
>> > NOEXEC mappings. Is that intentional or a side effect of the above
>> > masking bug?
>> >
>>
>> Yeah, my intention was to not stop the user of having heterogeneous
>> containers, as long as he doesn't care about using the NOEXEC flag. As
>> soon as the user tries to apply this flag however, then it should be
>> supported by all the IOMMUs behind the container - otherwise it is not
>> enforceable.
>>
>> Do you think we should change this behavior? I think most users will
>> not care about using this flag, and we should not stop them from
>> mixing containers.
>
> I think that's a reasonable way to go, but let's add a comment in uapi
> vfio.h describing that expectation. Thanks,
Ok, will do.
>
> Alex
>
>> >> while (iova < dma->iova + dma->size) {
>> >> phys_addr_t phys = iommu_iova_to_phys(d->domain, iova);
>> >> size_t size;
>> >> @@ -749,6 +763,9 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>> >> if (iommu_capable(bus, IOMMU_CAP_CACHE_COHERENCY))
>> >> domain->caps |= IOMMU_CAP_CACHE_COHERENCY;
>> >>
>> >> + if (iommu_capable(bus, IOMMU_CAP_NOEXEC))
>> >> + domain->caps |= IOMMU_CAP_NOEXEC;
>> >> +
>> >> /*
>> >> * Try to match an existing compatible domain. We don't want to
>> >> * preclude an IOMMU driver supporting multiple bus_types and being
>> >> @@ -900,6 +917,11 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>> >> return 0;
>> >> return vfio_domains_have_iommu_cap(iommu,
>> >> IOMMU_CAP_CACHE_COHERENCY);
>> >> + case VFIO_DMA_NOEXEC_IOMMU:
>> >> + if (!iommu)
>> >> + return 0;
>> >> + return vfio_domains_have_iommu_cap(iommu,
>> >> + IOMMU_CAP_NOEXEC);
>> >> default:
>> >> return 0;
>> >> }
>> >> @@ -923,7 +945,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>> >> } else if (cmd == VFIO_IOMMU_MAP_DMA) {
>> >> struct vfio_iommu_type1_dma_map map;
>> >> uint32_t mask = VFIO_DMA_MAP_FLAG_READ |
>> >> - VFIO_DMA_MAP_FLAG_WRITE;
>> >> + VFIO_DMA_MAP_FLAG_WRITE |
>> >> + VFIO_DMA_MAP_FLAG_NOEXEC;
>> >>
>> >> minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
>> >>
>> >
>> >
>> >
>>
>>
>>
>
>
>
--
Antonios Motakis
Virtual Open Systems
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