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 40enum { 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 76static 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 91static 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 121static 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 130static int via_rng_init(struct hwrng *rng) 131{ 132 struct cpuinfo_x86 *c = &cpu_data(0); 133 u32 lo, hi, old_lo; 134 135 /* VIA Nano CPUs don't have the MSR_VIA_RNG anymore. The RNG 136 * is always enabled if CPUID rng_en is set. There is no 137 * RNG configuration like it used to be the case in this 138 * register */ 139 if ((c->x86 == 6) && (c->x86_model >= 0x0f)) { 140 if (!cpu_has_xstore_enabled) { 141 printk(KERN_ERR PFX "can't enable hardware RNG " 142 "if XSTORE is not enabled\n"); 143 return -ENODEV; 144 } 145 return 0; 146 } 147 148 /* Control the RNG via MSR. Tread lightly and pay very close 149 * close attention to values written, as the reserved fields 150 * are documented to be "undefined and unpredictable"; but it 151 * does not say to write them as zero, so I make a guess that 152 * we restore the values we find in the register. 153 */ 154 rdmsr(MSR_VIA_RNG, lo, hi); 155 156 old_lo = lo; 157 lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT); 158 lo &= ~VIA_XSTORE_CNT_MASK; 159 lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE); 160 lo |= VIA_RNG_ENABLE; 161 lo |= VIA_NOISESRC1; 162 163 /* Enable secondary noise source on CPUs where it is present. */ 164 165 /* Nehemiah stepping 8 and higher */ 166 if ((c->x86_model == 9) && (c->x86_mask > 7)) 167 lo |= VIA_NOISESRC2; 168 169 /* Esther */ 170 if (c->x86_model >= 10) 171 lo |= VIA_NOISESRC2; 172 173 if (lo != old_lo) 174 wrmsr(MSR_VIA_RNG, lo, hi); 175 176 /* perhaps-unnecessary sanity check; remove after testing if 177 unneeded */ 178 rdmsr(MSR_VIA_RNG, lo, hi); 179 if ((lo & VIA_RNG_ENABLE) == 0) { 180 printk(KERN_ERR PFX "cannot enable VIA C3 RNG, aborting\n"); 181 return -ENODEV; 182 } 183 184 return 0; 185} 186 187 188static struct hwrng via_rng = { 189 .name = "via", 190 .init = via_rng_init, 191 .data_present = via_rng_data_present, 192 .data_read = via_rng_data_read, 193}; 194 195 196static int __init mod_init(void) 197{ 198 int err; 199 200 if (!cpu_has_xstore) 201 return -ENODEV; 202 printk(KERN_INFO "VIA RNG detected\n"); 203 err = hwrng_register(&via_rng); 204 if (err) { 205 printk(KERN_ERR PFX "RNG registering failed (%d)\n", 206 err); 207 goto out; 208 } 209out: 210 return err; 211} 212 213static void __exit mod_exit(void) 214{ 215 hwrng_unregister(&via_rng); 216} 217 218module_init(mod_init); 219module_exit(mod_exit); 220 221MODULE_DESCRIPTION("H/W RNG driver for VIA CPU with PadLock"); 222MODULE_LICENSE("GPL"); 223