drivers/firmware/efi/libstub/random.c

   1 /*
   2  * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  */
   9
  10 #include <linux/efi.h>
  11 #include <asm/efi.h>
  12
  13 #include "efistub.h"
  14
  15 struct efi_rng_protocol {
  16         efi_status_t (*get_info)(struct efi_rng_protocol *,
  17                                  unsigned long *, efi_guid_t *);
  18         efi_status_t (*get_rng)(struct efi_rng_protocol *,
  19                                 efi_guid_t *, unsigned long, u8 *out);
  20 };
  21
  22 efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
  23                                   unsigned long size, u8 *out)
  24 {
  25         efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
  26         efi_status_t status;
  27         struct efi_rng_protocol *rng;
  28
  29         status = efi_call_early(locate_protocol, &rng_proto, NULL,
  30                                 (void **)&rng);
  31         if (status != EFI_SUCCESS)
  32                 return status;
  33
  34         return rng->get_rng(rng, NULL, size, out);
  35 }
  36
  37 /*
  38  * Return the number of slots covered by this entry, i.e., the number of
  39  * addresses it covers that are suitably aligned and supply enough room
  40  * for the allocation.
  41  */
  42 static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
  43                                          unsigned long size,
  44                                          unsigned long align)
  45 {
  46         u64 start, end;
  47
  48         if (md->type != EFI_CONVENTIONAL_MEMORY)
  49                 return 0;
  50
  51         start = round_up(md->phys_addr, align);
  52         end = round_down(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - size,
  53                          align);
  54
  55         if (start > end)
  56                 return 0;
  57
  58         return (end - start + 1) / align;
  59 }
  60
  61 /*
  62  * The UEFI memory descriptors have a virtual address field that is only used
  63  * when installing the virtual mapping using SetVirtualAddressMap(). Since it
  64  * is unused here, we can reuse it to keep track of each descriptor's slot
  65  * count.
  66  */
  67 #define MD_NUM_SLOTS(md)        ((md)->virt_addr)
  68
  69 efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
  70                               unsigned long size,
  71                               unsigned long align,
  72                               unsigned long *addr,
  73                               unsigned long random_seed)
  74 {
  75         unsigned long map_size, desc_size, total_slots = 0, target_slot;
  76         unsigned long buff_size;
  77         efi_status_t status;
  78         efi_memory_desc_t *memory_map;
  79         int map_offset;
  80         struct efi_boot_memmap map;
  81
  82         map.map =       &memory_map;
  83         map.map_size =  &map_size;
  84         map.desc_size = &desc_size;
  85         map.desc_ver =  NULL;
  86         map.key_ptr =   NULL;
  87         map.buff_size = &buff_size;
  88
  89         status = efi_get_memory_map(sys_table_arg, &map);
  90         if (status != EFI_SUCCESS)
  91                 return status;
  92
  93         if (align < EFI_ALLOC_ALIGN)
  94                 align = EFI_ALLOC_ALIGN;
  95
  96         /* count the suitable slots in each memory map entry */
  97         for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
  98                 efi_memory_desc_t *md = (void *)memory_map + map_offset;
  99                 unsigned long slots;
 100
 101                 slots = get_entry_num_slots(md, size, align);
 102                 MD_NUM_SLOTS(md) = slots;
 103                 total_slots += slots;
 104         }
 105
 106         /* find a random number between 0 and total_slots */
 107         target_slot = (total_slots * (u16)random_seed) >> 16;
 108
 109         /*
 110          * target_slot is now a value in the range [0, total_slots), and so
 111          * it corresponds with exactly one of the suitable slots we recorded
 112          * when iterating over the memory map the first time around.
 113          *
 114          * So iterate over the memory map again, subtracting the number of
 115          * slots of each entry at each iteration, until we have found the entry
 116          * that covers our chosen slot. Use the residual value of target_slot
 117          * to calculate the randomly chosen address, and allocate it directly
 118          * using EFI_ALLOCATE_ADDRESS.
 119          */
 120         for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
 121                 efi_memory_desc_t *md = (void *)memory_map + map_offset;
 122                 efi_physical_addr_t target;
 123                 unsigned long pages;
 124
 125                 if (target_slot >= MD_NUM_SLOTS(md)) {
 126                         target_slot -= MD_NUM_SLOTS(md);
 127                         continue;
 128                 }
 129
 130                 target = round_up(md->phys_addr, align) + target_slot * align;
 131                 pages = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
 132
 133                 status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
 134                                         EFI_LOADER_DATA, pages, &target);
 135                 if (status == EFI_SUCCESS)
 136                         *addr = target;
 137                 break;
 138         }
 139
 140         efi_call_early(free_pool, memory_map);
 141
 142         return status;
 143 }