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 (!cpu_has_xstore_enabled) { 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 (!cpu_has_xstore) 204 return -ENODEV; 205 pr_info("VIA RNG detected\n"); 206 err = hwrng_register(&via_rng); 207 if (err) { 208 pr_err(PFX "RNG registering failed (%d)\n", 209 err); 210 goto out; 211 } 212 out: 213 return err; 214 } 215 216 static void __exit mod_exit(void) 217 { 218 hwrng_unregister(&via_rng); 219 } 220 221 module_init(mod_init); 222 module_exit(mod_exit); 223 224 static struct x86_cpu_id __maybe_unused via_rng_cpu_id[] = { 225 X86_FEATURE_MATCH(X86_FEATURE_XSTORE), 226 {} 227 }; 228 229 MODULE_DESCRIPTION("H/W RNG driver for VIA CPU with PadLock"); 230 MODULE_LICENSE("GPL"); 231 MODULE_DEVICE_TABLE(x86cpu, via_rng_cpu_id); 232