hw/misc/bcm2835_rng.c

   1 /*
   2  * BCM2835 Random Number Generator emulation
   3  *
   4  * Copyright (C) 2017 Marcin Chojnacki <marcinch7@gmail.com>
   5  *
   6  * This work is licensed under the terms of the GNU GPL, version 2 or later.
   7  * See the COPYING file in the top-level directory.
   8  */
   9
  10 #include "qemu/osdep.h"
  11 #include "qemu/log.h"
  12 #include "qemu/guest-random.h"
  13 #include "qemu/module.h"
  14 #include "hw/misc/bcm2835_rng.h"
  15 #include "migration/vmstate.h"
  16
  17 static uint32_t get_random_bytes(void)
  18 {
  19     uint32_t res;
  20
  21     /*
  22      * On failure we don't want to return the guest a non-random
  23      * value in case they're really using it for cryptographic
  24      * purposes, so the best we can do is die here.
  25      * This shouldn't happen unless something's broken.
  26      * In theory we could implement this device's full FIFO
  27      * and interrupt semantics and then just stop filling the
  28      * FIFO. That's a lot of work, though, so we assume any
  29      * errors are systematic problems and trust that if we didn't
  30      * fail as the guest inited then we won't fail later on
  31      * mid-run.
  32      */
  33     qemu_guest_getrandom_nofail(&res, sizeof(res));
  34     return res;
  35 }
  36
  37 static uint64_t bcm2835_rng_read(void *opaque, hwaddr offset,
  38                                  unsigned size)
  39 {
  40     BCM2835RngState *s = (BCM2835RngState *)opaque;
  41     uint32_t res = 0;
  42
  43     assert(size == 4);
  44
  45     switch (offset) {
  46     case 0x0:    /* rng_ctrl */
  47         res = s->rng_ctrl;
  48         break;
  49     case 0x4:    /* rng_status */
  50         res = s->rng_status | (1 << 24);
  51         break;
  52     case 0x8:    /* rng_data */
  53         res = get_random_bytes();
  54         break;
  55
  56     default:
  57         qemu_log_mask(LOG_GUEST_ERROR,
  58                       "bcm2835_rng_read: Bad offset %x\n",
  59                       (int)offset);
  60         res = 0;
  61         break;
  62     }
  63
  64     return res;
  65 }
  66
  67 static void bcm2835_rng_write(void *opaque, hwaddr offset,
  68                               uint64_t value, unsigned size)
  69 {
  70     BCM2835RngState *s = (BCM2835RngState *)opaque;
  71
  72     assert(size == 4);
  73
  74     switch (offset) {
  75     case 0x0:    /* rng_ctrl */
  76         s->rng_ctrl = value;
  77         break;
  78     case 0x4:    /* rng_status */
  79         /* we shouldn't let the guest write to bits [31..20] */
  80         s->rng_status &= ~0xFFFFF;        /* clear 20 lower bits */
  81         s->rng_status |= value & 0xFFFFF; /* set them to new value */
  82         break;
  83
  84     default:
  85         qemu_log_mask(LOG_GUEST_ERROR,
  86                       "bcm2835_rng_write: Bad offset %x\n",
  87                       (int)offset);
  88         break;
  89     }
  90 }
  91
  92 static const MemoryRegionOps bcm2835_rng_ops = {
  93     .read = bcm2835_rng_read,
  94     .write = bcm2835_rng_write,
  95     .endianness = DEVICE_NATIVE_ENDIAN,
  96 };
  97
  98 static const VMStateDescription vmstate_bcm2835_rng = {
  99     .name = TYPE_BCM2835_RNG,
 100     .version_id = 1,
 101     .minimum_version_id = 1,
 102     .fields = (VMStateField[]) {
 103         VMSTATE_UINT32(rng_ctrl, BCM2835RngState),
 104         VMSTATE_UINT32(rng_status, BCM2835RngState),
 105         VMSTATE_END_OF_LIST()
 106     }
 107 };
 108
 109 static void bcm2835_rng_init(Object *obj)
 110 {
 111     BCM2835RngState *s = BCM2835_RNG(obj);
 112
 113     memory_region_init_io(&s->iomem, obj, &bcm2835_rng_ops, s,
 114                           TYPE_BCM2835_RNG, 0x10);
 115     sysbus_init_mmio(SYS_BUS_DEVICE(s), &s->iomem);
 116 }
 117
 118 static void bcm2835_rng_reset(DeviceState *dev)
 119 {
 120     BCM2835RngState *s = BCM2835_RNG(dev);
 121
 122     s->rng_ctrl = 0;
 123     s->rng_status = 0;
 124 }
 125
 126 static void bcm2835_rng_class_init(ObjectClass *klass, void *data)
 127 {
 128     DeviceClass *dc = DEVICE_CLASS(klass);
 129
 130     dc->reset = bcm2835_rng_reset;
 131     dc->vmsd = &vmstate_bcm2835_rng;
 132 }
 133
 134 static const TypeInfo bcm2835_rng_info = {
 135     .name          = TYPE_BCM2835_RNG,
 136     .parent        = TYPE_SYS_BUS_DEVICE,
 137     .instance_size = sizeof(BCM2835RngState),
 138     .class_init    = bcm2835_rng_class_init,
 139     .instance_init = bcm2835_rng_init,
 140 };
 141
 142 static void bcm2835_rng_register_types(void)
 143 {
 144     type_register_static(&bcm2835_rng_info);
 145 }
 146
 147 type_init(bcm2835_rng_register_types)