[Qemu-devel] [PATCH v2 08/14] util: Add qemu_getrandom and support functions

[Richard Henderson]

Initialize the system from system and linux-user arguments.
Propagate deterministic seeds when creating new cpu threads.

Signed-off-by: Richard Henderson <address@hidden>
---
 include/qemu/random.h | 58 +++++++++++++++++++++++++++++++++++
 include/qom/cpu.h     |  1 +
 cpus.c                |  9 ++++++
 linux-user/main.c     | 21 ++++++-------
 linux-user/syscall.c  |  3 ++
 util/random.c         | 71 +++++++++++++++++++++++++++++++++++++++++++
 vl.c                  |  4 +++
 qemu-options.hx       | 10 ++++++
 util/Makefile.objs    |  1 +
 9 files changed, 167 insertions(+), 11 deletions(-)
 create mode 100644 include/qemu/random.h
 create mode 100644 util/random.c

diff --git a/include/qemu/random.h b/include/qemu/random.h
new file mode 100644
index 0000000000..9d88008288
--- /dev/null
+++ b/include/qemu/random.h
@@ -0,0 +1,58 @@
+/*
+ * QEMU random functions
+ *
+ * Copyright 2019 Linaro, Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#ifndef QEMU_RANDOM_H
+#define QEMU_RANDOM_H
+
+/**
+ * qemu_seedrandom_main(const char *optarg, Error **errp)
+ * @optarg: a non-NULL pointer to a C string
+ * @errp: an Error handler
+ *
+ * The @optarg value is that which accompanies the -seed argument.
+ * This forces qemu_getrandom into deterministic mode.
+ */
+void qemu_seedrandom_main(const char *optarg, Error **errp);
+
+/**
+ * qemu_seedrandom_thread_part1(void)
+ *
+ * If qemu_getrandom is in deterministic mode, returns an
+ * independant seed for the new thread.  Otherwise returns 0.
+ */
+uint64_t qemu_seedrandom_thread_part1(void);
+
+/**
+ * qemu_seedrandom_thread_part2(uint64_t seed)
+ * @seed: a value for the new thread.
+ *
+ * If qemu_getrandom is in deterministic mode, this stores an
+ * independant seed for the new thread.  Otherwise a no-op.
+ */
+void qemu_seedrandom_thread_part2(uint64_t seed);
+
+/**
+ * qemu_getrandom(void *buf, size_t len, bool nonblock)
+ * @buf: a buffer of bytes to be written
+ * @len: the number of bytes in @buf
+ * @nonblock: do not delay if the entropy pool is low
+ *
+ * Fills len bytes in buf with random data.  If nonblock is false,
+ * this may require a delay while the entropy pool fills.  Returns
+ * true if the call is successful, but the only non-successful case
+ * is when nonblock is true.
+ *
+ * The value of len must be <= 256, so that the BSD getentropy(3)
+ * function can be used to implement this.
+ */
+bool qemu_getrandom(void *buf, size_t len, bool nonblock);
+
+#endif /* QEMU_RANDOM_H */
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 1d6099e5d4..343cc6d51e 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -372,6 +372,7 @@ struct CPUState {
     int singlestep_enabled;
     int64_t icount_budget;
     int64_t icount_extra;
+    uint64_t random_seed;
     sigjmp_buf jmp_env;
 
     QemuMutex work_mutex;
diff --git a/cpus.c b/cpus.c
index e83f72b48b..b5d3f46220 100644
--- a/cpus.c
+++ b/cpus.c
@@ -49,6 +49,7 @@
 #include "qemu/option.h"
 #include "qemu/bitmap.h"
 #include "qemu/seqlock.h"
+#include "qemu/random.h"
 #include "tcg.h"
 #include "hw/nmi.h"
 #include "sysemu/replay.h"
@@ -1275,6 +1276,7 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
     /* signal CPU creation */
     cpu->created = true;
     qemu_cond_signal(&qemu_cpu_cond);
+    qemu_seedrandom_thread_part2(cpu->random_seed);
 
     do {
         if (cpu_can_run(cpu)) {
@@ -1318,6 +1320,7 @@ static void *qemu_dummy_cpu_thread_fn(void *arg)
     /* signal CPU creation */
     cpu->created = true;
     qemu_cond_signal(&qemu_cpu_cond);
+    qemu_seedrandom_thread_part2(cpu->random_seed);
 
     do {
         qemu_mutex_unlock_iothread();
@@ -1477,6 +1480,7 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg)
     cpu->created = true;
     cpu->can_do_io = 1;
     qemu_cond_signal(&qemu_cpu_cond);
+    qemu_seedrandom_thread_part2(cpu->random_seed);
 
     /* wait for initial kick-off after machine start */
     while (first_cpu->stopped) {
@@ -1591,6 +1595,7 @@ static void *qemu_hax_cpu_thread_fn(void *arg)
 
     hax_init_vcpu(cpu);
     qemu_cond_signal(&qemu_cpu_cond);
+    qemu_seedrandom_thread_part2(cpu->random_seed);
 
     do {
         if (cpu_can_run(cpu)) {
@@ -1630,6 +1635,7 @@ static void *qemu_hvf_cpu_thread_fn(void *arg)
     /* signal CPU creation */
     cpu->created = true;
     qemu_cond_signal(&qemu_cpu_cond);
+    qemu_seedrandom_thread_part2(cpu->random_seed);
 
     do {
         if (cpu_can_run(cpu)) {
@@ -1670,6 +1676,7 @@ static void *qemu_whpx_cpu_thread_fn(void *arg)
     /* signal CPU creation */
     cpu->created = true;
     qemu_cond_signal(&qemu_cpu_cond);
+    qemu_seedrandom_thread_part2(cpu->random_seed);
 
     do {
         if (cpu_can_run(cpu)) {
@@ -1723,6 +1730,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
     cpu->can_do_io = 1;
     current_cpu = cpu;
     qemu_cond_signal(&qemu_cpu_cond);
+    qemu_seedrandom_thread_part2(cpu->random_seed);
 
     /* process any pending work */
     cpu->exit_request = 1;
@@ -2070,6 +2078,7 @@ void qemu_init_vcpu(CPUState *cpu)
     cpu->nr_cores = smp_cores;
     cpu->nr_threads = smp_threads;
     cpu->stopped = true;
+    cpu->random_seed = qemu_seedrandom_thread_part1();
 
     if (!cpu->as) {
         /* If the target cpu hasn't set up any address spaces itself,
diff --git a/linux-user/main.c b/linux-user/main.c
index a0aba9cb1e..9682e81610 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -33,6 +33,7 @@
 #include "tcg.h"
 #include "qemu/timer.h"
 #include "qemu/envlist.h"
+#include "qemu/random.h"
 #include "elf.h"
 #include "trace/control.h"
 #include "target_elf.h"
@@ -47,6 +48,7 @@ static int gdbstub_port;
 static envlist_t *envlist;
 static const char *cpu_model;
 static const char *cpu_type;
+static const char *seed_optarg;
 unsigned long mmap_min_addr;
 unsigned long guest_base;
 int have_guest_base;
@@ -289,15 +291,9 @@ static void handle_arg_pagesize(const char *arg)
     }
 }
 
-static void handle_arg_randseed(const char *arg)
+static void handle_arg_seed(const char *arg)
 {
-    unsigned long long seed;
-
-    if (parse_uint_full(arg, &seed, 0) != 0 || seed > UINT_MAX) {
-        fprintf(stderr, "Invalid seed number: %s\n", arg);
-        exit(EXIT_FAILURE);
-    }
-    srand(seed);
+    seed_optarg = arg;
 }
 
 static void handle_arg_gdb(const char *arg)
@@ -432,7 +428,7 @@ static const struct qemu_argument arg_table[] = {
      "",           "run in singlestep mode"},
     {"strace",     "QEMU_STRACE",      false, handle_arg_strace,
      "",           "log system calls"},
-    {"seed",       "QEMU_RAND_SEED",   true,  handle_arg_randseed,
+    {"seed",       "QEMU_RAND_SEED",   true,  handle_arg_seed,
      "",           "Seed for pseudo-random number generator"},
     {"trace",      "QEMU_TRACE",       true,  handle_arg_trace,
      "",           "[[enable=]<pattern>][,events=<file>][,file=<file>]"},
@@ -687,8 +683,11 @@ int main(int argc, char **argv, char **envp)
         do_strace = 1;
     }
 
-    if (getenv("QEMU_RAND_SEED")) {
-        handle_arg_randseed(getenv("QEMU_RAND_SEED"));
+    if (seed_optarg == NULL) {
+        seed_optarg = getenv("QEMU_RAND_SEED");
+    }
+    if (seed_optarg != NULL) {
+        qemu_seedrandom_main(seed_optarg, &error_fatal);
     }
 
     target_environ = envlist_to_environ(envlist, NULL);
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 208fd1813d..18d98f5a08 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -110,6 +110,7 @@
 #include "uname.h"
 
 #include "qemu.h"
+#include "qemu/random.h"
 #include "fd-trans.h"
 
 #ifndef CLONE_IO
@@ -5448,6 +5449,7 @@ static void *clone_func(void *arg)
         put_user_u32(info->tid, info->child_tidptr);
     if (info->parent_tidptr)
         put_user_u32(info->tid, info->parent_tidptr);
+    qemu_seedrandom_thread_part2(cpu->random_seed);
     /* Enable signals.  */
     sigprocmask(SIG_SETMASK, &info->sigmask, NULL);
     /* Signal to the parent that we're ready.  */
@@ -5534,6 +5536,7 @@ static int do_fork(CPUArchState *env, unsigned int flags, 
abi_ulong newsp,
            initializing, so temporarily block all signals.  */
         sigfillset(&sigmask);
         sigprocmask(SIG_BLOCK, &sigmask, &info.sigmask);
+        cpu->random_seed = qemu_seedrandom_thread_part1();
 
         /* If this is our first additional thread, we need to ensure we
          * generate code for parallel execution and flush old translations.
diff --git a/util/random.c b/util/random.c
new file mode 100644
index 0000000000..467c987a66
--- /dev/null
+++ b/util/random.c
@@ -0,0 +1,71 @@
+/*
+ * QEMU random functions
+ *
+ * Copyright 2019 Linaro, Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "qemu/cutils.h"
+#include "qapi/error.h"
+#include "qemu/random.h"
+
+static __thread GRand *thread_rand;
+
+/* Deterministic implementation using Glib's Mersenne Twister.  */
+bool qemu_getrandom(void *buf, size_t len, bool nonblock)
+{
+    GRand *rand;
+    size_t i;
+    uint32_t x;
+
+    g_assert(len <= 256);
+
+    rand = thread_rand;
+    if (unlikely(rand == NULL)) {
+        /* Thread not initialized for a cpu, or main w/o -seed.  */
+        thread_rand = rand = g_rand_new();
+    }
+
+    for (i = 0; i + 4 <= len; i += 4) {
+        x = g_rand_int(rand);
+        __builtin_memcpy(buf + i, &x, 4);
+    }
+    if (i < len) {
+        x = g_rand_int(rand);
+        __builtin_memcpy(buf + i, &x, i - len);
+    }
+
+    return true;
+}
+
+uint64_t qemu_seedrandom_thread_part1(void)
+{
+    uint64_t ret;
+    qemu_getrandom(&ret, sizeof(ret), false);
+    return ret;
+}
+
+void qemu_seedrandom_thread_part2(uint64_t seed)
+{
+    g_assert(thread_rand == NULL);
+    thread_rand = g_rand_new_with_seed_array((const guint32 *)&seed,
+                                             sizeof(seed) / sizeof(guint32));
+}
+
+void qemu_seedrandom_main(const char *optarg, Error **errp)
+{
+    unsigned long long seed;
+    if (parse_uint_full(optarg, &seed, 0)) {
+        error_setg(errp, "Invalid seed number: %s", optarg);
+    } else {
+        g_assert(thread_rand != NULL);
+        g_rand_set_seed_array(thread_rand, (const guint32 *)&seed,
+                              sizeof(seed) / sizeof(guint32));
+    }
+}
diff --git a/vl.c b/vl.c
index c1d5484e12..0438b72f95 100644
--- a/vl.c
+++ b/vl.c
@@ -128,6 +128,7 @@ int main(int argc, char **argv)
 #include "qapi/qapi-commands-ui.h"
 #include "qapi/qmp/qerror.h"
 #include "sysemu/iothread.h"
+#include "qemu/random.h"
 
 #define MAX_VIRTIO_CONSOLES 1
 
@@ -3330,6 +3331,9 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_DFILTER:
                 qemu_set_dfilter_ranges(optarg, &error_fatal);
                 break;
+            case QEMU_OPTION_seed:
+                qemu_seedrandom_main(optarg, &error_fatal);
+                break;
             case QEMU_OPTION_s:
                 add_device_config(DEV_GDB, "tcp::" DEFAULT_GDBSTUB_PORT);
                 break;
diff --git a/qemu-options.hx b/qemu-options.hx
index 08749a3391..ed70de67d8 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3601,6 +3601,16 @@ the 0x200 sized block starting at 0xffffffc000080000 and 
another 0x1000 sized
 block starting at 0xffffffc00005f000.
 ETEXI
 
+DEF("seed", HAS_ARG, QEMU_OPTION_seed, \
+    "-seed number       seed the pseudo-random number generator\n",
+    QEMU_ARCH_ALL)
+STEXI
address@hidden -seed @var{number}
address@hidden -seed
+Force qemu to use a deterministic pseudo-random number generator,
+seeded with @var{number}.
+ETEXI
+
 DEF("L", HAS_ARG, QEMU_OPTION_L, \
     "-L path         set the directory for the BIOS, VGA BIOS and keymaps\n",
     QEMU_ARCH_ALL)
diff --git a/util/Makefile.objs b/util/Makefile.objs
index 835fcd69e2..bc7405c535 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -53,5 +53,6 @@ util-obj-y += iova-tree.o
 util-obj-$(CONFIG_INOTIFY1) += filemonitor-inotify.o
 util-obj-$(CONFIG_LINUX) += vfio-helpers.o
 util-obj-$(CONFIG_OPENGL) += drm.o
+util-obj-y += random.o
 
 stub-obj-y += filemonitor-stub.o
-- 
2.17.1