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 <crypto/padlock.h>
  28 #include <linux/module.h>
  29 #include <linux/kernel.h>
  30 #include <linux/hw_random.h>
  31 #include <linux/delay.h>
  32 #include <asm/cpu_device_id.h>
  33 #include <asm/io.h>
  34 #include <asm/msr.h>
  35 #include <asm/cpufeature.h>
  36 #include <asm/fpu/api.h>
  37
  38
  39
  40
  41 enum {
  42         VIA_STRFILT_CNT_SHIFT   = 16,
  43         VIA_STRFILT_FAIL        = (1 << 15),
  44         VIA_STRFILT_ENABLE      = (1 << 14),
  45         VIA_RAWBITS_ENABLE      = (1 << 13),
  46         VIA_RNG_ENABLE          = (1 << 6),
  47         VIA_NOISESRC1           = (1 << 8),
  48         VIA_NOISESRC2           = (1 << 9),
  49         VIA_XSTORE_CNT_MASK     = 0x0F,
  50
  51         VIA_RNG_CHUNK_8         = 0x00, /* 64 rand bits, 64 stored bits */
  52         VIA_RNG_CHUNK_4         = 0x01, /* 32 rand bits, 32 stored bits */
  53         VIA_RNG_CHUNK_4_MASK    = 0xFFFFFFFF,
  54         VIA_RNG_CHUNK_2         = 0x02, /* 16 rand bits, 32 stored bits */
  55         VIA_RNG_CHUNK_2_MASK    = 0xFFFF,
  56         VIA_RNG_CHUNK_1         = 0x03, /* 8 rand bits, 32 stored bits */
  57         VIA_RNG_CHUNK_1_MASK    = 0xFF,
  58 };
  59
  60 /*
  61  * Investigate using the 'rep' prefix to obtain 32 bits of random data
  62  * in one insn.  The upside is potentially better performance.  The
  63  * downside is that the instruction becomes no longer atomic.  Due to
  64  * this, just like familiar issues with /dev/random itself, the worst
  65  * case of a 'rep xstore' could potentially pause a cpu for an
  66  * unreasonably long time.  In practice, this condition would likely
  67  * only occur when the hardware is failing.  (or so we hope :))
  68  *
  69  * Another possible performance boost may come from simply buffering
  70  * until we have 4 bytes, thus returning a u32 at a time,
  71  * instead of the current u8-at-a-time.
  72  *
  73  * Padlock instructions can generate a spurious DNA fault, so
  74  * we have to call them in the context of irq_ts_save/restore()
  75  */
  76
  77 static inline u32 xstore(u32 *addr, u32 edx_in)
  78 {
  79         u32 eax_out;
  80         int ts_state;
  81
  82         ts_state = irq_ts_save();
  83
  84         asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */"
  85                 : "=m" (*addr), "=a" (eax_out), "+d" (edx_in), "+D" (addr));
  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         char buf[16 + PADLOCK_ALIGNMENT - STACK_ALIGN] __attribute__
  94                 ((aligned(STACK_ALIGN)));
  95         u32 *via_rng_datum = (u32 *)PTR_ALIGN(&buf[0], PADLOCK_ALIGNMENT);
  96         u32 bytes_out;
  97         int i;
  98
  99         /* We choose the recommended 1-byte-per-instruction RNG rate,
 100          * for greater randomness at the expense of speed.  Larger
 101          * values 2, 4, or 8 bytes-per-instruction yield greater
 102          * speed at lesser randomness.
 103          *
 104          * If you change this to another VIA_CHUNK_n, you must also
 105          * change the ->n_bytes values in rng_vendor_ops[] tables.
 106          * VIA_CHUNK_8 requires further code changes.
 107          *
 108          * A copy of MSR_VIA_RNG is placed in eax_out when xstore
 109          * completes.
 110          */
 111
 112         for (i = 0; i < 20; i++) {
 113                 *via_rng_datum = 0; /* paranoia, not really necessary */
 114                 bytes_out = xstore(via_rng_datum, VIA_RNG_CHUNK_1);
 115                 bytes_out &= VIA_XSTORE_CNT_MASK;
 116                 if (bytes_out || !wait)
 117                         break;
 118                 udelay(10);
 119         }
 120         rng->priv = *via_rng_datum;
 121         return bytes_out ? 1 : 0;
 122 }
 123
 124 static int via_rng_data_read(struct hwrng *rng, u32 *data)
 125 {
 126         u32 via_rng_datum = (u32)rng->priv;
 127
 128         *data = via_rng_datum;
 129
 130         return 1;
 131 }
 132
 133 static int via_rng_init(struct hwrng *rng)
 134 {
 135         struct cpuinfo_x86 *c = &cpu_data(0);
 136         u32 lo, hi, old_lo;
 137
 138         /* VIA Nano CPUs don't have the MSR_VIA_RNG anymore.  The RNG
 139          * is always enabled if CPUID rng_en is set.  There is no
 140          * RNG configuration like it used to be the case in this
 141          * register */
 142         if ((c->x86 == 6) && (c->x86_model >= 0x0f)) {
 143                 if (!boot_cpu_has(X86_FEATURE_XSTORE_EN)) {
 144                         pr_err(PFX "can't enable hardware RNG "
 145                                 "if XSTORE is not enabled\n");
 146                         return -ENODEV;
 147                 }
 148                 return 0;
 149         }
 150
 151         /* Control the RNG via MSR.  Tread lightly and pay very close
 152          * close attention to values written, as the reserved fields
 153          * are documented to be "undefined and unpredictable"; but it
 154          * does not say to write them as zero, so I make a guess that
 155          * we restore the values we find in the register.
 156          */
 157         rdmsr(MSR_VIA_RNG, lo, hi);
 158
 159         old_lo = lo;
 160         lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT);
 161         lo &= ~VIA_XSTORE_CNT_MASK;
 162         lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE);
 163         lo |= VIA_RNG_ENABLE;
 164         lo |= VIA_NOISESRC1;
 165
 166         /* Enable secondary noise source on CPUs where it is present. */
 167
 168         /* Nehemiah stepping 8 and higher */
 169         if ((c->x86_model == 9) && (c->x86_mask > 7))
 170                 lo |= VIA_NOISESRC2;
 171
 172         /* Esther */
 173         if (c->x86_model >= 10)
 174                 lo |= VIA_NOISESRC2;
 175
 176         if (lo != old_lo)
 177                 wrmsr(MSR_VIA_RNG, lo, hi);
 178
 179         /* perhaps-unnecessary sanity check; remove after testing if
 180            unneeded */
 181         rdmsr(MSR_VIA_RNG, lo, hi);
 182         if ((lo & VIA_RNG_ENABLE) == 0) {
 183                 pr_err(PFX "cannot enable VIA C3 RNG, aborting\n");
 184                 return -ENODEV;
 185         }
 186
 187         return 0;
 188 }
 189
 190
 191 static struct hwrng via_rng = {
 192         .name           = "via",
 193         .init           = via_rng_init,
 194         .data_present   = via_rng_data_present,
 195         .data_read      = via_rng_data_read,
 196 };
 197
 198
 199 static int __init mod_init(void)
 200 {
 201         int err;
 202
 203         if (!boot_cpu_has(X86_FEATURE_XSTORE))
 204                 return -ENODEV;
 205
 206         pr_info("VIA RNG detected\n");
 207         err = hwrng_register(&via_rng);
 208         if (err) {
 209                 pr_err(PFX "RNG registering failed (%d)\n",
 210                        err);
 211                 goto out;
 212         }
 213 out:
 214         return err;
 215 }
 216
 217 static void __exit mod_exit(void)
 218 {
 219         hwrng_unregister(&via_rng);
 220 }
 221
 222 module_init(mod_init);
 223 module_exit(mod_exit);
 224
 225 static struct x86_cpu_id __maybe_unused via_rng_cpu_id[] = {
 226         X86_FEATURE_MATCH(X86_FEATURE_XSTORE),
 227         {}
 228 };
 229
 230 MODULE_DESCRIPTION("H/W RNG driver for VIA CPU with PadLock");
 231 MODULE_LICENSE("GPL");
 232 MODULE_DEVICE_TABLE(x86cpu, via_rng_cpu_id);