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
41enum {
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
77static 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
87static 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(addr: via_rng_datum, edx_in: VIA_RNG_CHUNK_1);
111 bytes_out &= VIA_XSTORE_CNT_MASK;
112 if (bytes_out || !wait)
113 break;
114 udelay(usec: 10);
115 }
116 rng->priv = *via_rng_datum;
117 return bytes_out ? 1 : 0;
118}
119
120static 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
129static 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 * 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, low: lo, high: 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
187static 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
195static int __init via_rng_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(rng: &via_rng);
204 if (err) {
205 pr_err(PFX "RNG registering failed (%d)\n",
206 err);
207 goto out;
208 }
209out:
210 return err;
211}
212module_init(via_rng_mod_init);
213
214static void __exit via_rng_mod_exit(void)
215{
216 hwrng_unregister(rng: &via_rng);
217}
218module_exit(via_rng_mod_exit);
219
220static struct x86_cpu_id __maybe_unused via_rng_cpu_id[] = {
221 X86_MATCH_FEATURE(X86_FEATURE_XSTORE, NULL),
222 {}
223};
224MODULE_DEVICE_TABLE(x86cpu, via_rng_cpu_id);
225
226MODULE_DESCRIPTION("H/W RNG driver for VIA CPU with PadLock");
227MODULE_LICENSE("GPL");
228