summaryrefslogtreecommitdiffstats
path: root/arch/s390/boot/kaslr.c
blob: e8d74d4f62aa5ff0cd2284dc66dffca5a5e8ed56 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright IBM Corp. 2019
 */
#include <linux/pgtable.h>
#include <asm/mem_detect.h>
#include <asm/cpacf.h>
#include <asm/timex.h>
#include <asm/sclp.h>
#include <asm/kasan.h>
#include "decompressor.h"
#include "boot.h"

#define PRNG_MODE_TDES	 1
#define PRNG_MODE_SHA512 2
#define PRNG_MODE_TRNG	 3

struct prno_parm {
	u32 res;
	u32 reseed_counter;
	u64 stream_bytes;
	u8  V[112];
	u8  C[112];
};

struct prng_parm {
	u8  parm_block[32];
	u32 reseed_counter;
	u64 byte_counter;
};

static int check_prng(void)
{
	if (!cpacf_query_func(CPACF_KMC, CPACF_KMC_PRNG)) {
		sclp_early_printk("KASLR disabled: CPU has no PRNG\n");
		return 0;
	}
	if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG))
		return PRNG_MODE_TRNG;
	if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_SHA512_DRNG_GEN))
		return PRNG_MODE_SHA512;
	else
		return PRNG_MODE_TDES;
}

static int get_random(unsigned long limit, unsigned long *value)
{
	struct prng_parm prng = {
		/* initial parameter block for tdes mode, copied from libica */
		.parm_block = {
			0x0F, 0x2B, 0x8E, 0x63, 0x8C, 0x8E, 0xD2, 0x52,
			0x64, 0xB7, 0xA0, 0x7B, 0x75, 0x28, 0xB8, 0xF4,
			0x75, 0x5F, 0xD2, 0xA6, 0x8D, 0x97, 0x11, 0xFF,
			0x49, 0xD8, 0x23, 0xF3, 0x7E, 0x21, 0xEC, 0xA0
		},
	};
	unsigned long seed, random;
	struct prno_parm prno;
	__u64 entropy[4];
	int mode, i;

	mode = check_prng();
	seed = get_tod_clock_fast();
	switch (mode) {
	case PRNG_MODE_TRNG:
		cpacf_trng(NULL, 0, (u8 *) &random, sizeof(random));
		break;
	case PRNG_MODE_SHA512:
		cpacf_prno(CPACF_PRNO_SHA512_DRNG_SEED, &prno, NULL, 0,
			   (u8 *) &seed, sizeof(seed));
		cpacf_prno(CPACF_PRNO_SHA512_DRNG_GEN, &prno, (u8 *) &random,
			   sizeof(random), NULL, 0);
		break;
	case PRNG_MODE_TDES:
		/* add entropy */
		*(unsigned long *) prng.parm_block ^= seed;
		for (i = 0; i < 16; i++) {
			cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block,
				  (u8 *) entropy, (u8 *) entropy,
				  sizeof(entropy));
			memcpy(prng.parm_block, entropy, sizeof(entropy));
		}
		random = seed;
		cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block, (u8 *) &random,
			  (u8 *) &random, sizeof(random));
		break;
	default:
		return -1;
	}
	*value = random % limit;
	return 0;
}

/*
 * To randomize kernel base address we have to consider several facts:
 * 1. physical online memory might not be continuous and have holes. mem_detect
 *    info contains list of online memory ranges we should consider.
 * 2. we have several memory regions which are occupied and we should not
 *    overlap and destroy them. Currently safe_addr tells us the border below
 *    which all those occupied regions are. We are safe to use anything above
 *    safe_addr.
 * 3. the upper limit might apply as well, even if memory above that limit is
 *    online. Currently those limitations are:
 *    3.1. Limit set by "mem=" kernel command line option
 *    3.2. memory reserved at the end for kasan initialization.
 * 4. kernel base address must be aligned to THREAD_SIZE (kernel stack size).
 *    Which is required for CONFIG_CHECK_STACK. Currently THREAD_SIZE is 4 pages
 *    (16 pages when the kernel is built with kasan enabled)
 * Assumptions:
 * 1. kernel size (including .bss size) and upper memory limit are page aligned.
 * 2. mem_detect memory region start is THREAD_SIZE aligned / end is PAGE_SIZE
 *    aligned (in practice memory configurations granularity on z/VM and LPAR
 *    is 1mb).
 *
 * To guarantee uniform distribution of kernel base address among all suitable
 * addresses we generate random value just once. For that we need to build a
 * continuous range in which every value would be suitable. We can build this
 * range by simply counting all suitable addresses (let's call them positions)
 * which would be valid as kernel base address. To count positions we iterate
 * over online memory ranges. For each range which is big enough for the
 * kernel image we count all suitable addresses we can put the kernel image at
 * that is
 * (end - start - kernel_size) / THREAD_SIZE + 1
 * Two functions count_valid_kernel_positions and position_to_address help
 * to count positions in memory range given and then convert position back
 * to address.
 */
static unsigned long count_valid_kernel_positions(unsigned long kernel_size,
						  unsigned long _min,
						  unsigned long _max)
{
	unsigned long start, end, pos = 0;
	int i;

	for_each_mem_detect_block(i, &start, &end) {
		if (_min >= end)
			continue;
		if (start >= _max)
			break;
		start = max(_min, start);
		end = min(_max, end);
		if (end - start < kernel_size)
			continue;
		pos += (end - start - kernel_size) / THREAD_SIZE + 1;
	}

	return pos;
}

static unsigned long position_to_address(unsigned long pos, unsigned long kernel_size,
				 unsigned long _min, unsigned long _max)
{
	unsigned long start, end;
	int i;

	for_each_mem_detect_block(i, &start, &end) {
		if (_min >= end)
			continue;
		if (start >= _max)
			break;
		start = max(_min, start);
		end = min(_max, end);
		if (end - start < kernel_size)
			continue;
		if ((end - start - kernel_size) / THREAD_SIZE + 1 >= pos)
			return start + (pos - 1) * THREAD_SIZE;
		pos -= (end - start - kernel_size) / THREAD_SIZE + 1;
	}

	return 0;
}

unsigned long get_random_base(unsigned long safe_addr)
{
	unsigned long memory_limit = get_mem_detect_end();
	unsigned long base_pos, max_pos, kernel_size;
	unsigned long kasan_needs;
	int i;

	memory_limit = min(memory_limit, ident_map_size);

	/*
	 * Avoid putting kernel in the end of physical memory
	 * which kasan will use for shadow memory and early pgtable
	 * mapping allocations.
	 */
	memory_limit -= kasan_estimate_memory_needs(memory_limit);

	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_data.start && initrd_data.size) {
		if (safe_addr < initrd_data.start + initrd_data.size)
			safe_addr = initrd_data.start + initrd_data.size;
	}
	safe_addr = ALIGN(safe_addr, THREAD_SIZE);

	kernel_size = vmlinux.image_size + vmlinux.bss_size;
	if (safe_addr + kernel_size > memory_limit)
		return 0;

	max_pos = count_valid_kernel_positions(kernel_size, safe_addr, memory_limit);
	if (!max_pos) {
		sclp_early_printk("KASLR disabled: not enough memory\n");
		return 0;
	}

	/* we need a value in the range [1, base_pos] inclusive */
	if (get_random(max_pos, &base_pos))
		return 0;
	return position_to_address(base_pos + 1, kernel_size, safe_addr, memory_limit);
}