pnv/xive: Fix possible undefined shift error in group size calculation

Coverity discovered a potential shift overflow in group size calculation
in the case of a guest error. Add checks and logs to ensure a issues are
caught.

Make the group and crowd error checking code more similar to one another
while here.

Resolves: Coverity CID 1593724
Fixes: 9cb7f6ebed60 ("ppc/xive2: Support group-matching when looking for target")
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

1 files changed, 24 insertions, 3 deletions

diff --git a/hw/intc/xive.c b/hw/intc/xive.c
index e86f274932..3eb28c2265 100644
--- a/hw/intc/xive.c
+++ b/hw/intc/xive.c
@@ -1662,12 +1662,20 @@ uint32_t xive_get_vpgroup_size(uint32_t nvp_index)
      * (starting with the least significant bits) in the NVP index
      * gives the size of the group.
      */
-    return 1 << (ctz32(~nvp_index) + 1);
+    int first_zero = cto32(nvp_index);
+    if (first_zero >= 31) {
+        qemu_log_mask(LOG_GUEST_ERROR, "XIVE: Invalid group index 0x%08x",
+                                       nvp_index);
+        return 0;
+    }
+
+    return 1U << (first_zero + 1);
 }
 
 static uint8_t xive_get_group_level(bool crowd, bool ignore,
                                     uint32_t nvp_blk, uint32_t nvp_index)
 {
+    int first_zero;
     uint8_t level;
 
     if (!ignore) {
@@ -1675,12 +1683,25 @@ static uint8_t xive_get_group_level(bool crowd, bool ignore,
         return 0;
     }
 
-    level = (ctz32(~nvp_index) + 1) & 0b1111;
+    first_zero = cto32(nvp_index);
+    if (first_zero >= 31) {
+        qemu_log_mask(LOG_GUEST_ERROR, "XIVE: Invalid group index 0x%08x",
+                                       nvp_index);
+        return 0;
+    }
+
+    level = (first_zero + 1) & 0b1111;
     if (crowd) {
         uint32_t blk;
 
         /* crowd level is bit position of first 0 from the right in nvp_blk */
-        blk = ctz32(~nvp_blk) + 1;
+        first_zero = cto32(nvp_blk);
+        if (first_zero >= 31) {
+            qemu_log_mask(LOG_GUEST_ERROR, "XIVE: Invalid crowd block 0x%08x",
+                                           nvp_blk);
+            return 0;
+        }
+        blk = first_zero + 1;
 
         /*
          * Supported crowd sizes are 2^1, 2^2, and 2^4. 2^3 is not supported.