From 52485bbc38bfb6d92ae6ccc29023dd2d487c557d Mon Sep 17 00:00:00 2001
From: Hoa Nguyen <hoanguyen@ucdavis.edu>
Date: Wed, 16 Feb 2022 15:59:08 -0800
Subject: [PATCH] dev: Make VirtIORng device use gem5's rng instead of C++'s

Currently, VirtIORng uses C++'s RNG. This causes nondeterminism
across simulations using this device. One example is the example RISC-V
board booting Ubuntu,

configs/example/gem5_library/riscv-ubuntu-run.py

JIRA: https://gem5.atlassian.net/browse/GEM5-1193

Change-Id: I299e72eb891819007b4260390f5c2ba94d2dec7b
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/56889
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
---
 src/dev/virtio/VirtIORng.py |  2 --
 src/dev/virtio/rng.cc       | 28 +++++-----------------------
 src/dev/virtio/rng.hh       | 13 ++-----------
 3 files changed, 7 insertions(+), 36 deletions(-)

diff --git a/src/dev/virtio/VirtIORng.py b/src/dev/virtio/VirtIORng.py
index 54848ee7f1..13df059fa0 100644
--- a/src/dev/virtio/VirtIORng.py
+++ b/src/dev/virtio/VirtIORng.py
@@ -46,5 +46,3 @@ class VirtIORng(VirtIODeviceBase):
     cxx_class = 'gem5::VirtIORng'
 
     qSize = Param.Unsigned(16, "Request queue size")
-
-    entropy_source = Param.String("/dev/random", "The source of entropy")
diff --git a/src/dev/virtio/rng.cc b/src/dev/virtio/rng.cc
index 50a747ce98..c26568eb94 100644
--- a/src/dev/virtio/rng.cc
+++ b/src/dev/virtio/rng.cc
@@ -38,9 +38,7 @@
 
 #include "dev/virtio/rng.hh"
 
-#include <fcntl.h>
-#include <unistd.h>
-
+#include "base/random.hh"
 #include "debug/VIORng.hh"
 #include "params/VirtIORng.hh"
 #include "sim/system.hh"
@@ -50,8 +48,7 @@ namespace gem5
 
 VirtIORng::VirtIORng(const Params &params)
     : VirtIODeviceBase(params, ID_RNG, 0, 0),
-      qReq(params.system->physProxy, byteOrder, params.qSize,
-           params.entropy_source, *this)
+      qReq(params.system->physProxy, byteOrder, params.qSize, *this)
 {
     registerQueue(qReq);
 }
@@ -60,16 +57,10 @@ VirtIORng::~VirtIORng()
 {
 }
 
-VirtIORng::RngQueue::RngQueue(PortProxy &proxy, ByteOrder bo,
-    uint16_t size, const std::string &rng_file_path,
+VirtIORng::RngQueue::RngQueue(PortProxy &proxy, ByteOrder bo, uint16_t size,
     VirtIORng &_parent)
-    : VirtQueue(proxy, bo, size), parent(_parent), dist(0,255)
+    : VirtQueue(proxy, bo, size), parent(_parent)
 {
-    rng_fd = open(rng_file_path.c_str(), O_RDONLY);
-    if (rng_fd < 0) {
-        DPRINTF(VIORng, "error when open entropy source: %s\n",
-                rng_file_path.c_str());
-    }
 }
 
 void
@@ -89,16 +80,7 @@ VirtIORng::RngQueue::trySend()
         DPRINTF(VIORng, "Got descriptor (len: %i)\n", d->size());
         size_t len = 0;
         while (len < d->size()) {
-            uint8_t byte = 0;
-            bool rng_read_success = false;
-            if (rng_fd >= 0) {
-                ssize_t result = read(rng_fd, &byte, sizeof(uint8_t));
-                rng_read_success = (result > 0);
-            }
-            if (!rng_read_success) {
-                // fallback to C++ std rng generator
-                byte = dist(rd_device);
-            }
+            uint8_t byte = gem5::random_mt.random<uint8_t>();
             d->chainWrite(len, &byte, sizeof(uint8_t));
             ++len;
         }
diff --git a/src/dev/virtio/rng.hh b/src/dev/virtio/rng.hh
index 50a3723359..7be235421a 100644
--- a/src/dev/virtio/rng.hh
+++ b/src/dev/virtio/rng.hh
@@ -39,8 +39,6 @@
 #ifndef __DEV_VIRTIO_RNG_HH__
 #define __DEV_VIRTIO_RNG_HH__
 
-#include <random>
-
 #include "base/compiler.hh"
 #include "dev/virtio/base.hh"
 
@@ -76,9 +74,8 @@ class VirtIORng : public VirtIODeviceBase
         : public VirtQueue
     {
       public:
-        RngQueue(PortProxy &proxy, ByteOrder bo,
-                uint16_t size, const std::string &rng_file_path,
-                VirtIORng &_parent);
+        RngQueue(PortProxy &proxy, ByteOrder bo, uint16_t size,
+                 VirtIORng &_parent);
         virtual ~RngQueue() {}
 
         void onNotify() { trySend(); }
@@ -90,12 +87,6 @@ class VirtIORng : public VirtIODeviceBase
 
       protected:
         VirtIORng &parent;
-      private:
-        // system's special file for generating random number
-        int rng_fd;
-        // fallback random number generator
-        std::random_device rd_device;
-        std::uniform_int_distribution<int> dist;
     };
     /** Receive queue for port 0 */
     RngQueue qReq;