linux/arch/s390/boot/kaslr.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Copyright IBM Corp. 2019
   4 */
   5#include <linux/pgtable.h>
   6#include <asm/mem_detect.h>
   7#include <asm/cpacf.h>
   8#include <asm/timex.h>
   9#include <asm/sclp.h>
  10#include <asm/kasan.h>
  11#include "compressed/decompressor.h"
  12#include "boot.h"
  13
  14#define PRNG_MODE_TDES   1
  15#define PRNG_MODE_SHA512 2
  16#define PRNG_MODE_TRNG   3
  17
  18struct prno_parm {
  19        u32 res;
  20        u32 reseed_counter;
  21        u64 stream_bytes;
  22        u8  V[112];
  23        u8  C[112];
  24};
  25
  26struct prng_parm {
  27        u8  parm_block[32];
  28        u32 reseed_counter;
  29        u64 byte_counter;
  30};
  31
  32static int check_prng(void)
  33{
  34        if (!cpacf_query_func(CPACF_KMC, CPACF_KMC_PRNG)) {
  35                sclp_early_printk("KASLR disabled: CPU has no PRNG\n");
  36                return 0;
  37        }
  38        if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG))
  39                return PRNG_MODE_TRNG;
  40        if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_SHA512_DRNG_GEN))
  41                return PRNG_MODE_SHA512;
  42        else
  43                return PRNG_MODE_TDES;
  44}
  45
  46static int get_random(unsigned long limit, unsigned long *value)
  47{
  48        struct prng_parm prng = {
  49                /* initial parameter block for tdes mode, copied from libica */
  50                .parm_block = {
  51                        0x0F, 0x2B, 0x8E, 0x63, 0x8C, 0x8E, 0xD2, 0x52,
  52                        0x64, 0xB7, 0xA0, 0x7B, 0x75, 0x28, 0xB8, 0xF4,
  53                        0x75, 0x5F, 0xD2, 0xA6, 0x8D, 0x97, 0x11, 0xFF,
  54                        0x49, 0xD8, 0x23, 0xF3, 0x7E, 0x21, 0xEC, 0xA0
  55                },
  56        };
  57        unsigned long seed, random;
  58        struct prno_parm prno;
  59        __u64 entropy[4];
  60        int mode, i;
  61
  62        mode = check_prng();
  63        seed = get_tod_clock_fast();
  64        switch (mode) {
  65        case PRNG_MODE_TRNG:
  66                cpacf_trng(NULL, 0, (u8 *) &random, sizeof(random));
  67                break;
  68        case PRNG_MODE_SHA512:
  69                cpacf_prno(CPACF_PRNO_SHA512_DRNG_SEED, &prno, NULL, 0,
  70                           (u8 *) &seed, sizeof(seed));
  71                cpacf_prno(CPACF_PRNO_SHA512_DRNG_GEN, &prno, (u8 *) &random,
  72                           sizeof(random), NULL, 0);
  73                break;
  74        case PRNG_MODE_TDES:
  75                /* add entropy */
  76                *(unsigned long *) prng.parm_block ^= seed;
  77                for (i = 0; i < 16; i++) {
  78                        cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block,
  79                                  (u8 *) entropy, (u8 *) entropy,
  80                                  sizeof(entropy));
  81                        memcpy(prng.parm_block, entropy, sizeof(entropy));
  82                }
  83                random = seed;
  84                cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block, (u8 *) &random,
  85                          (u8 *) &random, sizeof(random));
  86                break;
  87        default:
  88                return -1;
  89        }
  90        *value = random % limit;
  91        return 0;
  92}
  93
  94/*
  95 * To randomize kernel base address we have to consider several facts:
  96 * 1. physical online memory might not be continuous and have holes. mem_detect
  97 *    info contains list of online memory ranges we should consider.
  98 * 2. we have several memory regions which are occupied and we should not
  99 *    overlap and destroy them. Currently safe_addr tells us the border below
 100 *    which all those occupied regions are. We are safe to use anything above
 101 *    safe_addr.
 102 * 3. the upper limit might apply as well, even if memory above that limit is
 103 *    online. Currently those limitations are:
 104 *    3.1. Limit set by "mem=" kernel command line option
 105 *    3.2. memory reserved at the end for kasan initialization.
 106 * 4. kernel base address must be aligned to THREAD_SIZE (kernel stack size).
 107 *    Which is required for CONFIG_CHECK_STACK. Currently THREAD_SIZE is 4 pages
 108 *    (16 pages when the kernel is built with kasan enabled)
 109 * Assumptions:
 110 * 1. kernel size (including .bss size) and upper memory limit are page aligned.
 111 * 2. mem_detect memory region start is THREAD_SIZE aligned / end is PAGE_SIZE
 112 *    aligned (in practice memory configurations granularity on z/VM and LPAR
 113 *    is 1mb).
 114 *
 115 * To guarantee uniform distribution of kernel base address among all suitable
 116 * addresses we generate random value just once. For that we need to build a
 117 * continuous range in which every value would be suitable. We can build this
 118 * range by simply counting all suitable addresses (let's call them positions)
 119 * which would be valid as kernel base address. To count positions we iterate
 120 * over online memory ranges. For each range which is big enough for the
 121 * kernel image we count all suitable addresses we can put the kernel image at
 122 * that is
 123 * (end - start - kernel_size) / THREAD_SIZE + 1
 124 * Two functions count_valid_kernel_positions and position_to_address help
 125 * to count positions in memory range given and then convert position back
 126 * to address.
 127 */
 128static unsigned long count_valid_kernel_positions(unsigned long kernel_size,
 129                                                  unsigned long _min,
 130                                                  unsigned long _max)
 131{
 132        unsigned long start, end, pos = 0;
 133        int i;
 134
 135        for_each_mem_detect_block(i, &start, &end) {
 136                if (_min >= end)
 137                        continue;
 138                if (start >= _max)
 139                        break;
 140                start = max(_min, start);
 141                end = min(_max, end);
 142                if (end - start < kernel_size)
 143                        continue;
 144                pos += (end - start - kernel_size) / THREAD_SIZE + 1;
 145        }
 146
 147        return pos;
 148}
 149
 150static unsigned long position_to_address(unsigned long pos, unsigned long kernel_size,
 151                                 unsigned long _min, unsigned long _max)
 152{
 153        unsigned long start, end;
 154        int i;
 155
 156        for_each_mem_detect_block(i, &start, &end) {
 157                if (_min >= end)
 158                        continue;
 159                if (start >= _max)
 160                        break;
 161                start = max(_min, start);
 162                end = min(_max, end);
 163                if (end - start < kernel_size)
 164                        continue;
 165                if ((end - start - kernel_size) / THREAD_SIZE + 1 >= pos)
 166                        return start + (pos - 1) * THREAD_SIZE;
 167                pos -= (end - start - kernel_size) / THREAD_SIZE + 1;
 168        }
 169
 170        return 0;
 171}
 172
 173unsigned long get_random_base(unsigned long safe_addr)
 174{
 175        unsigned long memory_limit = get_mem_detect_end();
 176        unsigned long base_pos, max_pos, kernel_size;
 177        unsigned long kasan_needs;
 178        int i;
 179
 180        memory_limit = min(memory_limit, ident_map_size);
 181
 182        /*
 183         * Avoid putting kernel in the end of physical memory
 184         * which kasan will use for shadow memory and early pgtable
 185         * mapping allocations.
 186         */
 187        memory_limit -= kasan_estimate_memory_needs(memory_limit);
 188
 189        if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && INITRD_START && INITRD_SIZE) {
 190                if (safe_addr < INITRD_START + INITRD_SIZE)
 191                        safe_addr = INITRD_START + INITRD_SIZE;
 192        }
 193        safe_addr = ALIGN(safe_addr, THREAD_SIZE);
 194
 195        kernel_size = vmlinux.image_size + vmlinux.bss_size;
 196        if (safe_addr + kernel_size > memory_limit)
 197                return 0;
 198
 199        max_pos = count_valid_kernel_positions(kernel_size, safe_addr, memory_limit);
 200        if (!max_pos) {
 201                sclp_early_printk("KASLR disabled: not enough memory\n");
 202                return 0;
 203        }
 204
 205        /* we need a value in the range [1, base_pos] inclusive */
 206        if (get_random(max_pos, &base_pos))
 207                return 0;
 208        return position_to_address(base_pos + 1, kernel_size, safe_addr, memory_limit);
 209}
 210