1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Entropy functions used on early boot for KASLR base and memory
4 * randomization. The base randomization is done in the compressed
5 * kernel and memory randomization is done early when the regular
6 * kernel starts. This file is included in the compressed kernel and
7 * normally linked in the regular.
8 */
9#include <asm/asm.h>
10#include <asm/kaslr.h>
11#include <asm/tsc.h>
12#include <asm/archrandom.h>
13#include <asm/e820/api.h>
14#include <asm/shared/io.h>
15
16/*
17 * When built for the regular kernel, several functions need to be stubbed out
18 * or changed to their regular kernel equivalent.
19 */
20#ifndef KASLR_COMPRESSED_BOOT
21#include <asm/cpufeature.h>
22#include <asm/setup.h>
23
24#define debug_putstr(v) early_printk("%s", v)
25#define has_cpuflag(f) boot_cpu_has(f)
26#define get_boot_seed() kaslr_offset()
27#endif
28
29#define I8254_PORT_CONTROL 0x43
30#define I8254_PORT_COUNTER0 0x40
31#define I8254_CMD_READBACK 0xC0
32#define I8254_SELECT_COUNTER0 0x02
33#define I8254_STATUS_NOTREADY 0x40
34static inline u16 i8254(void)
35{
36 u16 status, timer;
37
38 do {
39 outb(I8254_CMD_READBACK | I8254_SELECT_COUNTER0,
40 I8254_PORT_CONTROL);
41 status = inb(I8254_PORT_COUNTER0);
42 timer = inb(I8254_PORT_COUNTER0);
43 timer |= inb(I8254_PORT_COUNTER0) << 8;
44 } while (status & I8254_STATUS_NOTREADY);
45
46 return timer;
47}
48
49unsigned long kaslr_get_random_long(const char *purpose)
50{
51#ifdef CONFIG_X86_64
52 const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
53#else
54 const unsigned long mix_const = 0x3f39e593UL;
55#endif
56 unsigned long raw, random = get_boot_seed();
57 bool use_i8254 = true;
58
59 if (purpose) {
60 debug_putstr(purpose);
61 debug_putstr(" KASLR using");
62 }
63
64 if (has_cpuflag(X86_FEATURE_RDRAND)) {
65 if (purpose)
66 debug_putstr(" RDRAND");
67 if (rdrand_long(v: &raw)) {
68 random ^= raw;
69 use_i8254 = false;
70 }
71 }
72
73 if (has_cpuflag(X86_FEATURE_TSC)) {
74 if (purpose)
75 debug_putstr(" RDTSC");
76 raw = rdtsc();
77
78 random ^= raw;
79 use_i8254 = false;
80 }
81
82 if (use_i8254) {
83 if (purpose)
84 debug_putstr(" i8254");
85 random ^= i8254();
86 }
87
88 /* Circular multiply for better bit diffusion */
89 asm(_ASM_MUL "%3"
90 : "=a" (random), "=d" (raw)
91 : "a" (random), "rm" (mix_const));
92 random += raw;
93
94 if (purpose)
95 debug_putstr("...\n");
96
97 return random;
98}
99