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, but the 74 * kernel doesn't use CR0.TS, so this doesn't matter. 75 */ 76 77 static inline u32 xstore(u32 *addr, u32 edx_in) 78 { 79 u32 eax_out; 80 81 asm(".byte 0x0F,0xA7,0xC0 /* xstore %%edi (addr=%0) */" 82 : "=m" (*addr), "=a" (eax_out), "+d" (edx_in), "+D" (addr)); 83 84 return eax_out; 85 } 86 87 static int via_rng_data_present(struct hwrng *rng, int wait) 88 { 89 char buf[16 + PADLOCK_ALIGNMENT - STACK_ALIGN] __attribute__ 90 ((aligned(STACK_ALIGN))); 91 u32 *via_rng_datum = (u32 *)PTR_ALIGN(&buf[0], PADLOCK_ALIGNMENT); 92 u32 bytes_out; 93 int i; 94 95 /* We choose the recommended 1-byte-per-instruction RNG rate, 96 * for greater randomness at the expense of speed. Larger 97 * values 2, 4, or 8 bytes-per-instruction yield greater 98 * speed at lesser randomness. 99 * 100 * If you change this to another VIA_CHUNK_n, you must also 101 * change the ->n_bytes values in rng_vendor_ops[] tables. 102 * VIA_CHUNK_8 requires further code changes. 103 * 104 * A copy of MSR_VIA_RNG is placed in eax_out when xstore 105 * completes. 106 */ 107 108 for (i = 0; i < 20; i++) { 109 *via_rng_datum = 0; /* paranoia, not really necessary */ 110 bytes_out = xstore(via_rng_datum, VIA_RNG_CHUNK_1); 111 bytes_out &= VIA_XSTORE_CNT_MASK; 112 if (bytes_out || !wait) 113 break; 114 udelay(10); 115 } 116 rng->priv = *via_rng_datum; 117 return bytes_out ? 1 : 0; 118 } 119 120 static int via_rng_data_read(struct hwrng *rng, u32 *data) 121 { 122 u32 via_rng_datum = (u32)rng->priv; 123 124 *data = via_rng_datum; 125 126 return 1; 127 } 128 129 static int via_rng_init(struct hwrng *rng) 130 { 131 struct cpuinfo_x86 *c = &cpu_data(0); 132 u32 lo, hi, old_lo; 133 134 /* VIA Nano CPUs don't have the MSR_VIA_RNG anymore. The RNG 135 * is always enabled if CPUID rng_en is set. There is no 136 * RNG configuration like it used to be the case in this 137 * register */ 138 if (((c->x86 == 6) && (c->x86_model >= 0x0f)) || (c->x86 > 6)){ 139 if (!boot_cpu_has(X86_FEATURE_XSTORE_EN)) { 140 pr_err(PFX "can't enable hardware RNG " 141 "if XSTORE is not enabled\n"); 142 return -ENODEV; 143 } 144 return 0; 145 } 146 147 /* Control the RNG via MSR. Tread lightly and pay very close 148 * close attention to values written, as the reserved fields 149 * are documented to be "undefined and unpredictable"; but it 150 * does not say to write them as zero, so I make a guess that 151 * we restore the values we find in the register. 152 */ 153 rdmsr(MSR_VIA_RNG, lo, hi); 154 155 old_lo = lo; 156 lo &= ~(0x7f << VIA_STRFILT_CNT_SHIFT); 157 lo &= ~VIA_XSTORE_CNT_MASK; 158 lo &= ~(VIA_STRFILT_ENABLE | VIA_STRFILT_FAIL | VIA_RAWBITS_ENABLE); 159 lo |= VIA_RNG_ENABLE; 160 lo |= VIA_NOISESRC1; 161 162 /* Enable secondary noise source on CPUs where it is present. */ 163 164 /* Nehemiah stepping 8 and higher */ 165 if ((c->x86_model == 9) && (c->x86_stepping > 7)) 166 lo |= VIA_NOISESRC2; 167 168 /* Esther */ 169 if (c->x86_model >= 10) 170 lo |= VIA_NOISESRC2; 171 172 if (lo != old_lo) 173 wrmsr(MSR_VIA_RNG, lo, hi); 174 175 /* perhaps-unnecessary sanity check; remove after testing if 176 unneeded */ 177 rdmsr(MSR_VIA_RNG, lo, hi); 178 if ((lo & VIA_RNG_ENABLE) == 0) { 179 pr_err(PFX "cannot enable VIA C3 RNG, aborting\n"); 180 return -ENODEV; 181 } 182 183 return 0; 184 } 185 186 187 static struct hwrng via_rng = { 188 .name = "via", 189 .init = via_rng_init, 190 .data_present = via_rng_data_present, 191 .data_read = via_rng_data_read, 192 }; 193 194 195 static int __init mod_init(void) 196 { 197 int err; 198 199 if (!boot_cpu_has(X86_FEATURE_XSTORE)) 200 return -ENODEV; 201 202 pr_info("VIA RNG detected\n"); 203 err = hwrng_register(&via_rng); 204 if (err) { 205 pr_err(PFX "RNG registering failed (%d)\n", 206 err); 207 goto out; 208 } 209 out: 210 return err; 211 } 212 module_init(mod_init); 213 214 static void __exit mod_exit(void) 215 { 216 hwrng_unregister(&via_rng); 217 } 218 module_exit(mod_exit); 219 220 static struct x86_cpu_id __maybe_unused via_rng_cpu_id[] = { 221 X86_MATCH_FEATURE(X86_FEATURE_XSTORE, NULL), 222 {} 223 }; 224 MODULE_DEVICE_TABLE(x86cpu, via_rng_cpu_id); 225 226 MODULE_DESCRIPTION("H/W RNG driver for VIA CPU with PadLock"); 227 MODULE_LICENSE("GPL"); 228