[PATCH 1/3] hw/core/platform-bus: fix crash when num_irqs is zero

[Luigi Leonardi <leonardi@redhat.com>]

bitmap_new(0) returns a zero-size allocation, and the subsequent
bitmap_zero() dereferences it because small_nbits(0) is true.
Skip IRQ initialization entirely when num_irqs is zero, which is
valid for platform buses that only provide MMIO mapping.

This will be the case for the microvm platform bus which initially
has no IRQ lines.

Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
---
 hw/core/platform-bus.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/core/platform-bus.c b/hw/core/platform-bus.c
index a2217a2dee..4f765582e7 100644
--- a/hw/core/platform-bus.c
+++ b/hw/core/platform-bus.c
@@ -194,6 +194,10 @@ static void platform_bus_realize(DeviceState *dev, Error **errp)
                        pbus->mmio_size);
     sysbus_init_mmio(d, &pbus->mmio);
 
+    if (pbus->num_irqs == 0) {
+        return;
+    }
+
     pbus->used_irqs = bitmap_new(pbus->num_irqs);
     pbus->irqs = g_new0(qemu_irq, pbus->num_irqs);
     for (i = 0; i < pbus->num_irqs; i++) {

-- 
2.54.0