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
34 static 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
49 unsigned 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 }
99
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