fix(test_rng): check virtio_rng is not available through sysfs

On guest 6.1 on ARM instances we have a new paravirtualized SMCC
TRNG device, which breaks the assumptions of test_rng_not_present.
This patch changes the test to read the list of available hwrng devices
and assert virtio_rng is not preset.

Signed-off-by: Riccardo Mancini <[email protected]>

Author: Manciukic

tests/integration_tests/functional/test_rng.py

@@ -5,6 +5,7 @@
 import pytest
 
 from framework.utils import check_entropy
+from host_tools.network import SSHConnection
 
 
 @pytest.fixture(params=[None])
@@ -22,6 +23,15 @@ def uvm_with_rng(uvm_plain, request):
     return uvm
 
 
+def list_rng_available(ssh_connection: SSHConnection) -> list[str]:
+    """Returns a list of rng devices available in the VM"""
+    return (
+        ssh_connection.check_output("cat /sys/class/misc/hw_random/rng_available")
+        .stdout.strip()
+        .split()
+    )
+
+
 def test_rng_not_present(uvm_nano):
     """
     Test a guest microVM *without* an entropy device and ensure that
@@ -32,15 +42,9 @@ def test_rng_not_present(uvm_nano):
     vm.add_net_iface()
     vm.start()
 
-    # If the guest kernel has been built with the virtio-rng module
-    # the device should exist in the guest filesystem but we should
-    # not be able to get random numbers out of it.
-    cmd = "test -e /dev/hwrng"
-    vm.ssh.check_output(cmd)
-
-    cmd = "dd if=/dev/hwrng of=/dev/null bs=10 count=1"
-    ecode, _, _ = vm.ssh.run(cmd)
-    assert ecode == 1
+    assert not any(
+        rng.startswith("virtio_rng") for rng in list_rng_available(vm.ssh)
+    ), "virtio_rng device should not be available in the uvm"
 
 
 def test_rng_present(uvm_with_rng):