[PULL 02/10] vfio/spapr: Fix page size calculation

[David Gibson]

From: Alexey Kardashevskiy <address@hidden>

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 <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Greg Kurz <address@hidden>
Signed-off-by: David Gibson <address@hidden>
---
 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 33692fc86f..2900bd1941 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));
+    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",
-- 
2.25.2