On Tue, 24 Mar 2020 14:27:35 +0100
Philippe Mathieu-Daudé <phi...@redhat.com> wrote:
>
>
> On 3/24/20 7:39 AM, Alexey Kardashevskiy wrote:
> > Coverity detected an issue (CID 1421903) with potential call of clz64(0)
> > which returns 64 which make it do "<<" with a negative number.
> >
> > This checks the mask and avoids undefined behaviour.
> >
> > In practice pgsizes and memory_region_iommu_get_min_page_size() always
> > have some common page sizes and even if they did not, the resulting page
> > size would be 0x8000.0000.0000.0000 (gcc 9.2) and
> > ioctl(VFIO_IOMMU_SPAPR_TCE_CREATE) would fail anyway.
> >
> > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
> > ---
> > hw/vfio/spapr.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/vfio/spapr.c b/hw/vfio/spapr.c
> > index 33692fc86fd6..2900bd19417a 100644
> > --- a/hw/vfio/spapr.c
> > +++ b/hw/vfio/spapr.c
> > @@ -147,7 +147,7 @@ int vfio_spapr_create_window(VFIOContainer *container,
> > {
> > int ret = 0;
> > IOMMUMemoryRegion *iommu_mr = IOMMU_MEMORY_REGION(section->mr);
> > - uint64_t pagesize = memory_region_iommu_get_min_page_size(iommu_mr);
> > + uint64_t pagesize = memory_region_iommu_get_min_page_size(iommu_mr),
> > pgmask;
> > unsigned entries, bits_total, bits_per_level, max_levels;
> > struct vfio_iommu_spapr_tce_create create = { .argsz = sizeof(create)
> > };
> > long rampagesize = qemu_minrampagesize();
> > @@ -159,8 +159,8 @@ int vfio_spapr_create_window(VFIOContainer *container,
> > if (pagesize > rampagesize) {
> > pagesize = rampagesize;
> > }
> > - pagesize = 1ULL << (63 - clz64(container->pgsizes &
> > - (pagesize | (pagesize - 1))));
> > + pgmask = container->pgsizes & (pagesize | (pagesize - 1));
>
> Is that ROUND_UP(container->pgsizes, pagesize)?
>
This means we clip all page sizes greater than pagesize from
container->pgsizes... It doesn't look like ROUND_UP() semantics
to me.
> > + pagesize = pgmask ? (1ULL << (63 - clz64(pgmask))) : 0;
> > if (!pagesize) {
> > error_report("Host doesn't support page size 0x%"PRIx64
> > ", the supported mask is 0x%lx",
> >
>
>
