root/drivers/firmware/efi/libstub/random.c

DEFINITIONS

1. efi_get_random_bytes
2. get_entry_num_slots
3. efi_random_alloc
4. efi_random_get_seed

   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 
  12 struct 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 
  19 efi_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  */
  39 static 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 
  68 efi_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 
 144 efi_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 
 185 err_freepool:
 186         efi_call_early(free_pool, seed);
 187         return status;
 188 }