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

[Daniel P . Berrangé]

On Wed, Mar 13, 2019 at 09:55:20PM -0700, Richard Henderson wrote:
> 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 +++++++++++++++++++++++++++++++++++

I'm still not a fan of putting this stuff into such a generic
header as qemu/random.h, or calling it qemu_getrandom(). I'd
prefer something that make it clear that this is only for the
CPU emulation / userspace emulator usage.

Can we call it cpu-random.h perhaps, and qemu_cpu_getrandom()

>  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

Can we put a comment here saying it is only for use by TCG emulation
and userspace emulator helpers, and point people to crypto/random.h
for the preferred general purpose API.

Even though this is backed by the qcrypto_random by default, it could
be surprising if the -seed arg affected other callers.

> + *
> + * 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 */


I'm concerned that having this in a file qemu/ramdom.h will
still give a misleading impression that this is intended for
general purpose usage.

IIUC this is really designed for use by the e deterministic 


> 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,

It isn't clear that we should be needing these seeds in anything
other than the TCG codepath.

> 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",

Perhaps   -cpu-rand-seed  so indicate its only for the CPU emulation
parts ?

> +    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

Regards,
Daniel
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