[pentest] Fix fw override rng

Fix the fi rng test of using fw override. The test would only work more
than once in case the device is reset in between. Instead, we
re-initialize the fw override every call (we would like consecutive bits
so we stop the fifo after every call).
There was also a bug causing stack overflow by asking for bits in a for
loop whereas the full buffer was filled in a single loop.

Signed-off-by: Siemen Dhooghe <[email protected]>
(cherry picked from commit 7f48129)

Author: siemen11

sw/device/tests/penetrationtests/firmware/fi/rng_fi.c

@@ -41,9 +41,6 @@ static dif_entropy_src_t entropy_src;
 static dif_csrng_t csrng;
 static dif_edn_t edn0;
 static dif_edn_t edn1;
-static bool disable_health_check;
-
-static bool firmware_override_init;
 
 static const uint32_t kInputMsg[kCsrngBiasFWFifoBufferSize] = {
     0xa52a0da9, 0xcae141b2, 0x6d5bab9d, 0x2c3e5cc0, 0x225afc93, 0x5d31a610,
@@ -219,42 +216,42 @@ status_t handle_rng_fi_firmware_override(ujson_t *uj) {
   // Clear the AST recoverable alerts.
   pentest_clear_sensor_recov_alerts();
 
-  if (!firmware_override_init) {
-    // Check if we keep heal tests enabled.
-    rng_fi_fw_overwrite_health_t uj_data;
-    TRY(ujson_deserialize_rng_fi_fw_overwrite_health_t(uj, &uj_data));
-    disable_health_check = uj_data.disable_health_check;
-
-    firmware_override_init = true;
-  }
+  rng_fi_fw_overwrite_health_t uj_data;
+  TRY(ujson_deserialize_rng_fi_fw_overwrite_health_t(uj, &uj_data));
 
+  // Stop the entropy complex.
   TRY(entropy_testutils_stop_all());
 
-  if (disable_health_check) {
+  if (uj_data.disable_health_check) {
     // Disable all health tests.
     TRY(entropy_testutils_disable_health_tests(&entropy_src));
   }
 
+  // Enable firmware override mode
   TRY(entropy_testutils_fw_override_enable(&entropy_src, kEntropyFifoBufferSize,
                                            /*route_to_firmware=*/true,
                                            /*bypass_conditioner=*/true));
 
-  entropy_data_flush(&entropy_src);
+  // Flush any residual data in the observation FIFO.
+  size_t len;
+  do {
+    len = kEntropyFifoBufferSize;
+    TRY(dif_entropy_src_observe_fifo_nonblocking_read(&entropy_src, NULL,
+                                                      &len));
+  } while (len > 0);
 
   uint32_t buf[kEntropyFifoBufferSize] = {0};
 
   pentest_set_trigger_high();
   asm volatile(NOP30);
-  for (size_t it = 0; it < kEntropyFifoBufferSize; it++) {
-    while (buf[it] == 0) {
-      TRY(dif_entropy_src_observe_fifo_blocking_read(&entropy_src, &buf[it],
-                                                     kEntropyFifoBufferSize));
-    }
-  }
+  TRY(dif_entropy_src_observe_fifo_blocking_read(&entropy_src, buf,
+                                                 kEntropyFifoBufferSize));
 
   asm volatile(NOP30);
   pentest_set_trigger_low();
 
+  TRY(entropy_testutils_stop_all());
+
   // Get registered alerts from alert handler.
   reg_alerts = pentest_get_triggered_alerts();
   // Get registered local alerts from alert handler.
@@ -434,9 +431,6 @@ status_t handle_rng_fi_edn_init(ujson_t *uj) {
   TRY(dif_edn_init(mmio_region_from_addr(TOP_EARLGREY_EDN0_BASE_ADDR), &edn0));
   TRY(dif_edn_init(mmio_region_from_addr(TOP_EARLGREY_EDN1_BASE_ADDR), &edn1));
 
-  firmware_override_init = false;
-
-  // Read different SKU config fields and return to host.
   TRY(pentest_send_sku_config(uj));
 
   return OK_STATUS();

sw/host/penetrationtests/python/fi/host_scripts/fi_rng_functions.py

@@ -74,19 +74,18 @@ def char_entropy_bias(target, iterations, reset = False):
     return response
 
 
-def char_fw_overwrite(target, iterations, disable_health_check):
+def char_fw_overwrite(target, iterations, disable_health_check, reset = False):
     rngfi = OTFIRng(target)
-
-    for _ in range(iterations):
+    if reset:
         target.reset_target()
         # Clear the output from the reset
         target.dump_all()
-
-        # Initialize our chip and catch its output
-        device_id, sensors, alerts, owner_page, boot_log, boot_measurements, version = (
-            rngfi.init("char_fw_overwrite",
-                       alert_config=common_library.default_fpga_friendly_alert_config)
-        )
+    # Initialize our chip and catch its output
+    device_id, sensors, alerts, owner_page, boot_log, boot_measurements, version = (
+        rngfi.init("char_fw_overwrite",
+                   alert_config=common_library.default_fpga_friendly_alert_config)
+    )
+    for _ in range(iterations):
         rngfi.rng_fw_overwrite(disable_health_check)
         response = target.read_response()
     return response