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/msr.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(&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}