drivers/char/hw_random/via-rng.c

   1 /*
   2  * RNG driver for VIA RNGs
   3  *
   4  * Copyright 2005 (c) MontaVista Software, Inc.
   5  *
   6  * with the majority of the code coming from:
   7  *
   8  * Hardware driver for the Intel/AMD/VIA Random Number Generators (RNG)
   9  * (c) Copyright 2003 Red Hat Inc <jgarzik@redhat.com>
  10  *
  11  * derived from
  12  *
  13  * Hardware driver for the AMD 768 Random Number Generator (RNG)
  14  * (c) Copyright 2001 Red Hat Inc
  15  *
  16  * derived from
  17  *
  18  * Hardware driver for Intel i810 Random Number Generator (RNG)
  19  * Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
  20  * Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>
  21  *
  22  * This file is licensed under  the terms of the GNU General Public
  23  * License version 2. This program is licensed "as is" without any
  24  * warranty of any kind, whether express or implied.
  25  */
  26
  27 #include <linux/module.h>
  28 #include <linux/kernel.h>
  29 #include <linux/hw_random.h>
  30 #include <linux/delay.h>
  31 #include <asm/io.h>
  32 #include <asm/msr.h>
  33 #include <asm/cpufeature.h>
  34 #include <asm/i387.h>
  35
  36
  37 #define PFX     KBUILD_MODNAME ": "
  38
  39
  40 enum {
  41         VIA_STRFILT_CNT_SHIFT   = 16,
  42         VIA_STRFILT_FAIL        = (1 << 15),
  43         VIA_STRFILT_ENABLE      = (1 << 14),
  44         VIA_RAWBITS_ENABLE      = (1 << 13),
  45         VIA_RNG_ENABLE          = (1 << 6),
  46         VIA_NOISESRC1           = (1 << 8),
  47         VIA_NOISESRC2           = (1 << 9),
  48         VIA_XSTORE_CNT_MASK     = 0x0F,
  49
  50         VIA_RNG_CHUNK_8         = 0x00, /* 64 rand bits, 64 stored bits */
  51         VIA_RNG_CHUNK_4         = 0x01, /* 32 rand bits, 32 stored bits */
  52         VIA_RNG_CHUNK_4_MASK    = 0xFFFFFFFF,
  53         VIA_RNG_CHUNK_2         = 0x02, /* 16 rand bits, 32 stored bits */
  54         VIA_RNG_CHUNK_2_MASK    = 0xFFFF,
  55         VIA_RNG_CHUNK_1         = 0x03, /* 8 rand bits, 32 stored bits */
  56         VIA_RNG_CHUNK_1_MASK    = 0xFF,
  57 };
  58
  59 /*
  60  * Investigate using the 'rep' prefix to obtain 32 bits of random data
  61  * in one insn.  The upside is potentially better performance.  The
  62  * downside is that the instruction becomes no longer atomic.  Due to
  63  * this, just like familiar issues with /dev/random itself, the worst
  64  * case of a 'rep xstore' could potentially pause a cpu for an
  65  * unreasonably long time.  In practice, this condition would likely
  66  * only occur when the hardware is failing.  (or so we hope :))
  67  *
  68  * Another possible performance boost may come from simply buffering
  69  * until we have 4 bytes, thus returning a u32 at a time,
  70  * instead of the current u8-at-a-time.
  71  *
  72  * Padlock instructions can generate a spurious DNA fault, so
  73  * we have to call them in the context of irq_ts_save/restore()
  74  */
  75
  76 static inline u32 xstore(u32 *addr, u32 edx_in)
  77 {
  78         u32 eax_out;
  79         int ts_state;
  80
  81         ts_state = irq_ts_save();
  82
  83         asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */"
  84                 :"=m"(*addr), "=a"(eax_out)
  85                 :"D"(addr), "d"(edx_in));
  86
  87         irq_ts_restore(ts_state);
  88         return eax_out;
  89 }
  90
  91 static int via_rng_data_present(struct hwrng *rng, int wait)
  92 {
  93         u32 bytes_out;
  94         u32 *via_rng_datum = (u32 *)(&rng->priv);
  95         int i;
  96
  97         /* We choose the recommended 1-byte-per-instruction RNG rate,
  98          * for greater randomness at the expense of speed.  Larger
  99          * values 2, 4, or 8 bytes-per-instruction yield greater
 100          * speed at lesser randomness.
 101          *
 102          * If you change this to another VIA_CHUNK_n, you must also
 103          * change the ->n_bytes values in rng_vendor_ops[] tables.
 104          * VIA_CHUNK_8 requires further code changes.
 105          *
 106          * A copy of MSR_VIA_RNG is placed in eax_out when xstore
 107          * completes.
 108          */
 109
 110         for (i = 0; i < 20; i++) {
 111                 *via_rng_datum = 0; /* paranoia, not really necessary */
 112                 bytes_out = xstore(via_rng_datum, VIA_RNG_CHUNK_1);
 113                 bytes_out &= VIA_XSTORE_CNT_MASK;
 114                 if (bytes_out || !wait)
 115                         break;
 116                 udelay(10);
 117         }
 118         return bytes_out ? 1 : 0;
 119 }
 120
 121 static int via_rng_data_read(struct hwrng *rng, u32 *data)
 122 {
 123         u32 via_rng_datum = (u32)rng->priv;
 124
 125         *data = via_rng_datum;
 126
 127         return 1;
 128 }
 129
 130 static int via_rng_init(struct hwrng *rng)
 131 {
 132         struct cpuinfo_x86 *c = &cpu_data(0);
 133         u32 lo, hi, old_lo;
 134
 135         /* Control the RNG via MSR.  Tread lightly and pay very close
 136          * close attention to values written, as the reserved fields
 137          * are documented to be "undefined and unpredictable"; but it
 138          * does not say to write them as zero, so I make a guess that
 139          * we restore the values we find in the register.
 140          */
 141         rdmsr(MSR_VIA_RNG, lo, hi);
 142
 143         old_lo = lo;
 144         lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT);
 145         lo &= ~VIA_XSTORE_CNT_MASK;
 146         lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE);
 147         lo |= VIA_RNG_ENABLE;
 148         lo |= VIA_NOISESRC1;
 149
 150         /* Enable secondary noise source on CPUs where it is present. */
 151
 152         /* Nehemiah stepping 8 and higher */
 153         if ((c->x86_model == 9) && (c->x86_mask > 7))
 154                 lo |= VIA_NOISESRC2;
 155
 156         /* Esther */
 157         if (c->x86_model >= 10)
 158                 lo |= VIA_NOISESRC2;
 159
 160         if (lo != old_lo)
 161                 wrmsr(MSR_VIA_RNG, lo, hi);
 162
 163         /* perhaps-unnecessary sanity check; remove after testing if
 164            unneeded */
 165         rdmsr(MSR_VIA_RNG, lo, hi);
 166         if ((lo & VIA_RNG_ENABLE) == 0) {
 167                 printk(KERN_ERR PFX "cannot enable VIA C3 RNG, aborting\n");
 168                 return -ENODEV;
 169         }
 170
 171         return 0;
 172 }
 173
 174
 175 static struct hwrng via_rng = {
 176         .name           = "via",
 177         .init           = via_rng_init,
 178         .data_present   = via_rng_data_present,
 179         .data_read      = via_rng_data_read,
 180 };
 181
 182
 183 static int __init mod_init(void)
 184 {
 185         int err;
 186
 187         if (!cpu_has_xstore)
 188                 return -ENODEV;
 189         printk(KERN_INFO "VIA RNG detected\n");
 190         err = hwrng_register(&via_rng);
 191         if (err) {
 192                 printk(KERN_ERR PFX "RNG registering failed (%d)\n",
 193                        err);
 194                 goto out;
 195         }
 196 out:
 197         return err;
 198 }
 199
 200 static void __exit mod_exit(void)
 201 {
 202         hwrng_unregister(&via_rng);
 203 }
 204
 205 module_init(mod_init);
 206 module_exit(mod_exit);
 207
 208 MODULE_DESCRIPTION("H/W RNG driver for VIA chipsets");
 209 MODULE_LICENSE("GPL");