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/io.h> 33 #include <asm/msr.h> 34 #include <asm/cpufeature.h> 35 #include <asm/i387.h> 36 37 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), "+d" (edx_in), "+D" (addr)); 85 86 irq_ts_restore(ts_state); 87 return eax_out; 88 } 89 90 static int via_rng_data_present(struct hwrng *rng, int wait) 91 { 92 char buf[16 + PADLOCK_ALIGNMENT - STACK_ALIGN] __attribute__ 93 ((aligned(STACK_ALIGN))); 94 u32 *via_rng_datum = (u32 *)PTR_ALIGN(&buf[0], PADLOCK_ALIGNMENT); 95 u32 bytes_out; 96 int i; 97 98 /* We choose the recommended 1-byte-per-instruction RNG rate, 99 * for greater randomness at the expense of speed. Larger 100 * values 2, 4, or 8 bytes-per-instruction yield greater 101 * speed at lesser randomness. 102 * 103 * If you change this to another VIA_CHUNK_n, you must also 104 * change the ->n_bytes values in rng_vendor_ops[] tables. 105 * VIA_CHUNK_8 requires further code changes. 106 * 107 * A copy of MSR_VIA_RNG is placed in eax_out when xstore 108 * completes. 109 */ 110 111 for (i = 0; i < 20; i++) { 112 *via_rng_datum = 0; /* paranoia, not really necessary */ 113 bytes_out = xstore(via_rng_datum, VIA_RNG_CHUNK_1); 114 bytes_out &= VIA_XSTORE_CNT_MASK; 115 if (bytes_out || !wait) 116 break; 117 udelay(10); 118 } 119 rng->priv = *via_rng_datum; 120 return bytes_out ? 1 : 0; 121 } 122 123 static int via_rng_data_read(struct hwrng *rng, u32 *data) 124 { 125 u32 via_rng_datum = (u32)rng->priv; 126 127 *data = via_rng_datum; 128 129 return 1; 130 } 131 132 static int via_rng_init(struct hwrng *rng) 133 { 134 struct cpuinfo_x86 *c = &cpu_data(0); 135 u32 lo, hi, old_lo; 136 137 /* VIA Nano CPUs don't have the MSR_VIA_RNG anymore. The RNG 138 * is always enabled if CPUID rng_en is set. There is no 139 * RNG configuration like it used to be the case in this 140 * register */ 141 if ((c->x86 == 6) && (c->x86_model >= 0x0f)) { 142 if (!cpu_has_xstore_enabled) { 143 printk(KERN_ERR PFX "can't enable hardware RNG " 144 "if XSTORE is not enabled\n"); 145 return -ENODEV; 146 } 147 return 0; 148 } 149 150 /* Control the RNG via MSR. Tread lightly and pay very close 151 * close attention to values written, as the reserved fields 152 * are documented to be "undefined and unpredictable"; but it 153 * does not say to write them as zero, so I make a guess that 154 * we restore the values we find in the register. 155 */ 156 rdmsr(MSR_VIA_RNG, lo, hi); 157 158 old_lo = lo; 159 lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT); 160 lo &= ~VIA_XSTORE_CNT_MASK; 161 lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE); 162 lo |= VIA_RNG_ENABLE; 163 lo |= VIA_NOISESRC1; 164 165 /* Enable secondary noise source on CPUs where it is present. */ 166 167 /* Nehemiah stepping 8 and higher */ 168 if ((c->x86_model == 9) && (c->x86_mask > 7)) 169 lo |= VIA_NOISESRC2; 170 171 /* Esther */ 172 if (c->x86_model >= 10) 173 lo |= VIA_NOISESRC2; 174 175 if (lo != old_lo) 176 wrmsr(MSR_VIA_RNG, lo, hi); 177 178 /* perhaps-unnecessary sanity check; remove after testing if 179 unneeded */ 180 rdmsr(MSR_VIA_RNG, lo, hi); 181 if ((lo & VIA_RNG_ENABLE) == 0) { 182 printk(KERN_ERR PFX "cannot enable VIA C3 RNG, aborting\n"); 183 return -ENODEV; 184 } 185 186 return 0; 187 } 188 189 190 static struct hwrng via_rng = { 191 .name = "via", 192 .init = via_rng_init, 193 .data_present = via_rng_data_present, 194 .data_read = via_rng_data_read, 195 }; 196 197 198 static int __init mod_init(void) 199 { 200 int err; 201 202 if (!cpu_has_xstore) 203 return -ENODEV; 204 printk(KERN_INFO "VIA RNG detected\n"); 205 err = hwrng_register(&via_rng); 206 if (err) { 207 printk(KERN_ERR PFX "RNG registering failed (%d)\n", 208 err); 209 goto out; 210 } 211 out: 212 return err; 213 } 214 215 static void __exit mod_exit(void) 216 { 217 hwrng_unregister(&via_rng); 218 } 219 220 module_init(mod_init); 221 module_exit(mod_exit); 222 223 MODULE_DESCRIPTION("H/W RNG driver for VIA CPU with PadLock"); 224 MODULE_LICENSE("GPL"); 225