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 {
  21         unsigned long align = 1UL << align_shift;
  22         u64 first_slot, last_slot, region_end;
  23
  24         if (md->type != EFI_CONVENTIONAL_MEMORY)
  25                 return 0;
  26
  27         if (efi_soft_reserve_enabled() &&
  28             (md->attribute & EFI_MEMORY_SP))
  29                 return 0;
  30
  31         region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1,
  32                          (u64)ULONG_MAX);
  33
  34         first_slot = round_up(md->phys_addr, align);
  35         last_slot = round_down(region_end - size + 1, align);
  36
  37         if (first_slot > last_slot)
  38                 return 0;
  39
  40         return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
  41 }
  42
  43 /*
  44  * The UEFI memory descriptors have a virtual address field that is only used
  45  * when installing the virtual mapping using SetVirtualAddressMap(). Since it
  46  * is unused here, we can reuse it to keep track of each descriptor's slot
  47  * count.
  48  */
  49 #define MD_NUM_SLOTS(md)        ((md)->virt_addr)
  50
  51 efi_status_t efi_random_alloc(unsigned long size,
  52                               unsigned long align,
  53                               unsigned long *addr,
  54                               unsigned long random_seed)
  55 {
  56         unsigned long map_size, desc_size, total_slots = 0, target_slot;
  57         unsigned long buff_size;
  58         efi_status_t status;
  59         efi_memory_desc_t *memory_map;
  60         int map_offset;
  61         struct efi_boot_memmap map;
  62
  63         map.map =       &memory_map;
  64         map.map_size =  &map_size;
  65         map.desc_size = &desc_size;
  66         map.desc_ver =  NULL;
  67         map.key_ptr =   NULL;
  68         map.buff_size = &buff_size;
  69
  70         status = efi_get_memory_map(&map);
  71         if (status != EFI_SUCCESS)
  72                 return status;
  73
  74         if (align < EFI_ALLOC_ALIGN)
  75                 align = EFI_ALLOC_ALIGN;
  76
  77         size = round_up(size, EFI_ALLOC_ALIGN);
  78
  79         /* count the suitable slots in each memory map entry */
  80         for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
  81                 efi_memory_desc_t *md = (void *)memory_map + map_offset;
  82                 unsigned long slots;
  83
  84                 slots = get_entry_num_slots(md, size, ilog2(align));
  85                 MD_NUM_SLOTS(md) = slots;
  86                 total_slots += slots;
  87         }
  88
  89         /* find a random number between 0 and total_slots */
  90         target_slot = (total_slots * (u16)random_seed) >> 16;
  91
  92         /*
  93          * target_slot is now a value in the range [0, total_slots), and so
  94          * it corresponds with exactly one of the suitable slots we recorded
  95          * when iterating over the memory map the first time around.
  96          *
  97          * So iterate over the memory map again, subtracting the number of
  98          * slots of each entry at each iteration, until we have found the entry
  99          * that covers our chosen slot. Use the residual value of target_slot
 100          * to calculate the randomly chosen address, and allocate it directly
 101          * using EFI_ALLOCATE_ADDRESS.
 102          */
 103         for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
 104                 efi_memory_desc_t *md = (void *)memory_map + map_offset;
 105                 efi_physical_addr_t target;
 106                 unsigned long pages;
 107
 108                 if (target_slot >= MD_NUM_SLOTS(md)) {
 109                         target_slot -= MD_NUM_SLOTS(md);
 110                         continue;
 111                 }
 112
 113                 target = round_up(md->phys_addr, align) + target_slot * align;
 114                 pages = size / EFI_PAGE_SIZE;
 115
 116                 status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
 117                                      EFI_LOADER_DATA, pages, &target);
 118                 if (status == EFI_SUCCESS)
 119                         *addr = target;
 120                 break;
 121         }
 122
 123         efi_bs_call(free_pool, memory_map);
 124
 125         return status;
 126 }