LXR linux/drivers/firmware/efi/libstub/random.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
   4 */
   5
   6#include <linux/efi.h>
   7#include <linux/log2.h>
   8#include <asm/efi.h>
   9
  10#include "efistub.h"
  11
  12struct efi_rng_protocol {
  13        efi_status_t (*get_info)(struct efi_rng_protocol *,
  14                                 unsigned long *, efi_guid_t *);
  15        efi_status_t (*get_rng)(struct efi_rng_protocol *,
  16                                efi_guid_t *, unsigned long, u8 *out);
  17};
  18
  19efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
  20                                  unsigned long size, u8 *out)
  21{
  22        efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
  23        efi_status_t status;
  24        struct efi_rng_protocol *rng;
  25
  26        status = efi_call_early(locate_protocol, &rng_proto, NULL,
  27                                (void **)&rng);
  28        if (status != EFI_SUCCESS)
  29                return status;
  30
  31        return rng->get_rng(rng, NULL, size, out);
  32}
  33
  34/*
  35 * Return the number of slots covered by this entry, i.e., the number of
  36 * addresses it covers that are suitably aligned and supply enough room
  37 * for the allocation.
  38 */
  39static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
  40                                         unsigned long size,
  41                                         unsigned long align_shift)
  42{
  43        unsigned long align = 1UL << align_shift;
  44        u64 first_slot, last_slot, region_end;
  45
  46        if (md->type != EFI_CONVENTIONAL_MEMORY)
  47                return 0;
  48
  49        region_end = min((u64)ULONG_MAX, md->phys_addr + md->num_pages*EFI_PAGE_SIZE - 1);
  50
  51        first_slot = round_up(md->phys_addr, align);
  52        last_slot = round_down(region_end - size + 1, align);
  53
  54        if (first_slot > last_slot)
  55                return 0;
  56
  57        return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
  58}
  59
  60/*
  61 * The UEFI memory descriptors have a virtual address field that is only used
  62 * when installing the virtual mapping using SetVirtualAddressMap(). Since it
  63 * is unused here, we can reuse it to keep track of each descriptor's slot
  64 * count.
  65 */
  66#define MD_NUM_SLOTS(md)        ((md)->virt_addr)
  67
  68efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
  69                              unsigned long size,
  70                              unsigned long align,
  71                              unsigned long *addr,
  72                              unsigned long random_seed)
  73{
  74        unsigned long map_size, desc_size, total_slots = 0, target_slot;
  75        unsigned long buff_size;
  76        efi_status_t status;
  77        efi_memory_desc_t *memory_map;
  78        int map_offset;
  79        struct efi_boot_memmap map;
  80
  81        map.map =       &memory_map;
  82        map.map_size =  &map_size;
  83        map.desc_size = &desc_size;
  84        map.desc_ver =  NULL;
  85        map.key_ptr =   NULL;
  86        map.buff_size = &buff_size;
  87
  88        status = efi_get_memory_map(sys_table_arg, &map);
  89        if (status != EFI_SUCCESS)
  90                return status;
  91
  92        if (align < EFI_ALLOC_ALIGN)
  93                align = EFI_ALLOC_ALIGN;
  94
  95        /* count the suitable slots in each memory map entry */
  96        for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
  97                efi_memory_desc_t *md = (void *)memory_map + map_offset;
  98                unsigned long slots;
  99
 100                slots = get_entry_num_slots(md, size, ilog2(align));
 101                MD_NUM_SLOTS(md) = slots;
 102                total_slots += slots;
 103        }
 104
 105        /* find a random number between 0 and total_slots */
 106        target_slot = (total_slots * (u16)random_seed) >> 16;
 107
 108        /*
 109         * target_slot is now a value in the range [0, total_slots), and so
 110         * it corresponds with exactly one of the suitable slots we recorded
 111         * when iterating over the memory map the first time around.
 112         *
 113         * So iterate over the memory map again, subtracting the number of
 114         * slots of each entry at each iteration, until we have found the entry
 115         * that covers our chosen slot. Use the residual value of target_slot
 116         * to calculate the randomly chosen address, and allocate it directly
 117         * using EFI_ALLOCATE_ADDRESS.
 118         */
 119        for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
 120                efi_memory_desc_t *md = (void *)memory_map + map_offset;
 121                efi_physical_addr_t target;
 122                unsigned long pages;
 123
 124                if (target_slot >= MD_NUM_SLOTS(md)) {
 125                        target_slot -= MD_NUM_SLOTS(md);
 126                        continue;
 127                }
 128
 129                target = round_up(md->phys_addr, align) + target_slot * align;
 130                pages = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
 131
 132                status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
 133                                        EFI_LOADER_DATA, pages, &target);
 134                if (status == EFI_SUCCESS)
 135                        *addr = target;
 136                break;
 137        }
 138
 139        efi_call_early(free_pool, memory_map);
 140
 141        return status;
 142}
 143
 144efi_status_t efi_random_get_seed(efi_system_table_t *sys_table_arg)
 145{
 146        efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
 147        efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
 148        efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
 149        struct efi_rng_protocol *rng;
 150        struct linux_efi_random_seed *seed;
 151        efi_status_t status;
 152
 153        status = efi_call_early(locate_protocol, &rng_proto, NULL,
 154                                (void **)&rng);
 155        if (status != EFI_SUCCESS)
 156                return status;
 157
 158        status = efi_call_early(allocate_pool, EFI_RUNTIME_SERVICES_DATA,
 159                                sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
 160                                (void **)&seed);
 161        if (status != EFI_SUCCESS)
 162                return status;
 163
 164        status = rng->get_rng(rng, &rng_algo_raw, EFI_RANDOM_SEED_SIZE,
 165                              seed->bits);
 166        if (status == EFI_UNSUPPORTED)
 167                /*
 168                 * Use whatever algorithm we have available if the raw algorithm
 169                 * is not implemented.
 170                 */
 171                status = rng->get_rng(rng, NULL, EFI_RANDOM_SEED_SIZE,
 172                                      seed->bits);
 173
 174        if (status != EFI_SUCCESS)
 175                goto err_freepool;
 176
 177        seed->size = EFI_RANDOM_SEED_SIZE;
 178        status = efi_call_early(install_configuration_table, &rng_table_guid,
 179                                seed);
 180        if (status != EFI_SUCCESS)
 181                goto err_freepool;
 182
 183        return EFI_SUCCESS;
 184
 185err_freepool:
 186        efi_call_early(free_pool, seed);
 187        return status;
 188}
 189