On Wed, 2016-01-20 at 16:14 +0100, Pierre Morel wrote:
>
> On 01/12/2016 07:16 PM, Alex Williamson wrote:
> > On Tue, 2016-01-12 at 16:11 +0100, Pierre Morel wrote:
> > > In vfio_listener_region_add(), we try to validate that the region
> > > is
> > > not
> > > zero sized and hasn't overflowed the addresses space.
> > >
> > > But the calculation uses the size of the region instead of
> > > using the region's limit (size - 1).
> > >
> > > This leads to Int128 overflow when the region has
> > > been initialized to UINT64_MAX because in this case
> > > memory_region_init() transform the size from UINT64_MAX
> > > to int128_2_64().
> > >
> > > Let's really use the limit by sustracting one to the size
> > > and take care to use the limit for functions using limit
> > > and size to call functions which need size.
> > >
> > > Signed-off-by: Pierre Morel <pmo...@linux.vnet.ibm.com>
> > > ---
> > >
> > > Changes from v2:
> > > - all, just ignore v2, sorry about this,
> > > this is build after v1
> > >
> > > Changes from v1:
> > > - adjust the tests by knowing we already substracted one to
> > > end.
> > >
> > > hw/vfio/common.c | 14 +++++++-------
> > > 1 files changed, 7 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > > index 6797208..a5f6643 100644
> > > --- a/hw/vfio/common.c
> > > +++ b/hw/vfio/common.c
> > > @@ -348,12 +348,12 @@ static void
> > > vfio_listener_region_add(MemoryListener *listener,
> > > if (int128_ge(int128_make64(iova), llend)) {
> > > return;
> > > }
> > > - end = int128_get64(llend);
> > > + end = int128_get64(int128_sub(llend, int128_one()));
> > >
> > > - if ((iova < container->min_iova) || ((end - 1) > container-
> > > > max_iova)) {
> > > + if ((iova < container->min_iova) || (end > container-
> > > > max_iova)) {
> > > error_report("vfio: IOMMU container %p can't map guest
> > > IOVA
> > > region"
> > > " 0x%"HWADDR_PRIx"..0x%"HWADDR_PRIx,
> > > - container, iova, end - 1);
> > > + container, iova, end);
> > > ret = -EFAULT;
> > > goto fail;
> > > }
> > > @@ -363,7 +363,7 @@ static void
> > > vfio_listener_region_add(MemoryListener *listener,
> > > if (memory_region_is_iommu(section->mr)) {
> > > VFIOGuestIOMMU *giommu;
> > >
> > > - trace_vfio_listener_region_add_iommu(iova, end - 1);
> > > + trace_vfio_listener_region_add_iommu(iova, end);
> > > /*
> > > * FIXME: We should do some checking to see if the
> > > * capabilities of the host VFIO IOMMU are adequate to
> > > model
> > > @@ -394,13 +394,13 @@ static void
> > > vfio_listener_region_add(MemoryListener *listener,
> > > section->offset_within_region +
> > > (iova - section->offset_within_address_space);
> > >
> > > - trace_vfio_listener_region_add_ram(iova, end - 1, vaddr);
> > > + trace_vfio_listener_region_add_ram(iova, end, vaddr);
> > >
> > > - ret = vfio_dma_map(container, iova, end - iova, vaddr,
> > > section-
> > > > readonly);
> > > + ret = vfio_dma_map(container, iova, end - iova + 1, vaddr,
> > > section->readonly);
> > > if (ret) {
> > > error_report("vfio_dma_map(%p, 0x%"HWADDR_PRIx", "
> > > "0x%"HWADDR_PRIx", %p) = %d (%m)",
> > > - container, iova, end - iova, vaddr, ret);
> > > + container, iova, end - iova + 1, vaddr,
> > > ret);
> > > goto fail;
> > > }
> > >
> > Hmm, did we just push the overflow from one place to another? If
> > we're
> > mapping a full region of size int128_2_64() starting at iova zero,
> > then
> > this becomes (0xffff_ffff_ffff_ffff - 0 + 1) = 0. So I think we
> > need
> > to calculate size with 128bit arithmetic too and let it assert if
> > we
> > overflow, ie:
> >
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index a5f6643..13ad90b 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -321,7 +321,7 @@ static void
> > vfio_listener_region_add(MemoryListener *listener,
> > MemoryRegionSection
> > *section)
> > {
> > VFIOContainer *container = container_of(listener,
> > VFIOContainer, listener);
> > - hwaddr iova, end;
> > + hwaddr iova, end, size;
> > Int128 llend;
> > void *vaddr;
> > int ret;
> > @@ -348,7 +348,9 @@ static void
> > vfio_listener_region_add(MemoryListener *listener,
> > if (int128_ge(int128_make64(iova), llend)) {
> > return;
> > }
> > +
> > end = int128_get64(int128_sub(llend, int128_one()));
> > + size = int128_get64(int128_sub(llend, int128_make64(iova)));
>
> here again, if iova is null, since llend is section->size (2^64) ...
>
> >
> > if ((iova < container->min_iova) || (end > container-
> > >max_iova)) {
> > error_report("vfio: IOMMU container %p can't map guest
> > IOVA region"
> > @@ -396,11 +398,11 @@ static void
> > vfio_listener_region_add(MemoryListener *listener,
> >
> > trace_vfio_listener_region_add_ram(iova, end, vaddr);
> >
> > - ret = vfio_dma_map(container, iova, end - iova + 1, vaddr,
> > section->readonly);
> > + ret = vfio_dma_map(container, iova, size, vaddr, section-
> > >readonly);
> > if (ret) {
> > error_report("vfio_dma_map(%p, 0x%"HWADDR_PRIx", "
> > "0x%"HWADDR_PRIx", %p) = %d (%m)",
> > - container, iova, end - iova + 1, vaddr, ret);
> > + container, iova, size, vaddr, ret);
> > goto fail;
> > }
> >
> >
> > Does that still solve your scenario? Perhaps vfio-iommu-type1
> > should
> > have used first/last rather than start/size for mapping since we
> > seem
> > to have an off-by-one for mapping a full 64bit space. Seems like
> > we
> > could do it with two calls to vfio_dma_map if we really wanted to.
> > Thanks,
> >
> > Alex
> >
>
> You are right, every try to solve this will push the overflow
> somewhere
> else.
>
> There is just no way to express 2^64 with 64 bits, we have the
> int128()
> solution,
> but if we solve it here, we fall in the linux ioctl call anyway.
>
> Intuitively, making two calls do not seem right to me.
>
> But, what do you think of something like:
>
> - creating a new VFIO extention
>
> - and in ioctl(), since we have a flag entry in the
> vfio_iommu_type1_dma_map,
> may be adding a new flag meaning "map all virtual memory" ?
> or meaning "use first/last" ?
> I think this would break existing code unless we add a new VFIO
> extension.
Backup, is there ever a case where we actually need to map the entire
64bit address space? This is fairly well impossible on x86. I'm
pointing out an issue, but I don't know that we need to solve it with
more than an assert since it's never likely to happen. Thanks,
Alex
