drivers/firmware/efi/libstub/randomalloc.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
  12 /*
  13  * Return the number of slots covered by this entry, i.e., the number of
  14  * addresses it covers that are suitably aligned and supply enough room
  15  * for the allocation.
  16  */
  17 static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
  18                                          unsigned long size,
  19                                          unsigned long align_shift,
  20                                          u64 alloc_min, u64 alloc_max)
  21 {
  22         unsigned long align = 1UL << align_shift;
  23         u64 first_slot, last_slot, region_end;
  24
  25         if (md->type != EFI_CONVENTIONAL_MEMORY)
  26                 return 0;
  27
  28         if (efi_soft_reserve_enabled() &&
  29             (md->attribute & EFI_MEMORY_SP))
  30                 return 0;
  31
  32         region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1,
  33                          alloc_max);
  34         if (region_end < size)
  35                 return 0;
  36
  37         first_slot = round_up(max(md->phys_addr, alloc_min), align);
  38         last_slot = round_down(region_end - size + 1, align);
  39
  40         if (first_slot > last_slot)
  41                 return 0;
  42
  43         return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
  44 }
  45
  46 /*
  47  * The UEFI memory descriptors have a virtual address field that is only used
  48  * when installing the virtual mapping using SetVirtualAddressMap(). Since it
  49  * is unused here, we can reuse it to keep track of each descriptor's slot
  50  * count.
  51  */
  52 #define MD_NUM_SLOTS(md)        ((md)->virt_addr)
  53
  54 efi_status_t efi_random_alloc(unsigned long size,
  55                               unsigned long align,
  56                               unsigned long *addr,
  57                               unsigned long random_seed,
  58                               int memory_type,
  59                               unsigned long alloc_min,
  60                               unsigned long alloc_max)
  61 {
  62         struct efi_boot_memmap *map __free(efi_pool) = NULL;
  63         unsigned long total_slots = 0, target_slot;
  64         unsigned long total_mirrored_slots = 0;
  65         efi_status_t status;
  66         int map_offset;
  67
  68         status = efi_get_memory_map(&map, false);
  69         if (status != EFI_SUCCESS)
  70                 return status;
  71
  72         if (align < EFI_ALLOC_ALIGN)
  73                 align = EFI_ALLOC_ALIGN;
  74
  75         size = round_up(size, EFI_ALLOC_ALIGN);
  76
  77         /* count the suitable slots in each memory map entry */
  78         for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
  79                 efi_memory_desc_t *md = (void *)map->map + map_offset;
  80                 unsigned long slots;
  81
  82                 slots = get_entry_num_slots(md, size, ilog2(align), alloc_min,
  83                                             alloc_max);
  84                 MD_NUM_SLOTS(md) = slots;
  85                 total_slots += slots;
  86                 if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
  87                         total_mirrored_slots += slots;
  88         }
  89
  90         /* consider only mirrored slots for randomization if any exist */
  91         if (total_mirrored_slots > 0)
  92                 total_slots = total_mirrored_slots;
  93
  94         /* find a random number between 0 and total_slots */
  95         target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
  96
  97         /*
  98          * target_slot is now a value in the range [0, total_slots), and so
  99          * it corresponds with exactly one of the suitable slots we recorded
 100          * when iterating over the memory map the first time around.
 101          *
 102          * So iterate over the memory map again, subtracting the number of
 103          * slots of each entry at each iteration, until we have found the entry
 104          * that covers our chosen slot. Use the residual value of target_slot
 105          * to calculate the randomly chosen address, and allocate it directly
 106          * using EFI_ALLOCATE_ADDRESS.
 107          */
 108         status = EFI_OUT_OF_RESOURCES;
 109         for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
 110                 efi_memory_desc_t *md = (void *)map->map + map_offset;
 111                 efi_physical_addr_t target;
 112                 unsigned long pages;
 113
 114                 if (total_mirrored_slots > 0 &&
 115                     !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
 116                         continue;
 117
 118                 if (target_slot >= MD_NUM_SLOTS(md)) {
 119                         target_slot -= MD_NUM_SLOTS(md);
 120                         continue;
 121                 }
 122
 123                 target = round_up(max_t(u64, md->phys_addr, alloc_min), align) + target_slot * align;
 124                 pages = size / EFI_PAGE_SIZE;
 125
 126                 status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
 127                                      memory_type, pages, &target);
 128                 if (status == EFI_SUCCESS)
 129                         *addr = target;
 130                 break;
 131         }
 132
 133         return status;
 134 }