xref: /openbmc/linux/arch/x86/lib/kaslr.c (revision adb5680b)
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
i8254(void)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 
kaslr_get_random_long(const char * purpose)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