LXR linux/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 */
  17static 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        if (region_end < size)
  34                return 0;
  35
  36        first_slot = round_up(md->phys_addr, align);
  37        last_slot = round_down(region_end - size + 1, align);
  38
  39        if (first_slot > last_slot)
  40                return 0;
  41
  42        return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
  43}
  44
  45/*
  46 * The UEFI memory descriptors have a virtual address field that is only used
  47 * when installing the virtual mapping using SetVirtualAddressMap(). Since it
  48 * is unused here, we can reuse it to keep track of each descriptor's slot
  49 * count.
  50 */
  51#define MD_NUM_SLOTS(md)        ((md)->virt_addr)
  52
  53efi_status_t efi_random_alloc(unsigned long size,
  54                              unsigned long align,
  55                              unsigned long *addr,
  56                              unsigned long random_seed)
  57{
  58        unsigned long map_size, desc_size, total_slots = 0, target_slot;
  59        unsigned long buff_size;
  60        efi_status_t status;
  61        efi_memory_desc_t *memory_map;
  62        int map_offset;
  63        struct efi_boot_memmap map;
  64
  65        map.map =       &memory_map;
  66        map.map_size =  &map_size;
  67        map.desc_size = &desc_size;
  68        map.desc_ver =  NULL;
  69        map.key_ptr =   NULL;
  70        map.buff_size = &buff_size;
  71
  72        status = efi_get_memory_map(&map);
  73        if (status != EFI_SUCCESS)
  74                return status;
  75
  76        if (align < EFI_ALLOC_ALIGN)
  77                align = EFI_ALLOC_ALIGN;
  78
  79        size = round_up(size, EFI_ALLOC_ALIGN);
  80
  81        /* count the suitable slots in each memory map entry */
  82        for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
  83                efi_memory_desc_t *md = (void *)memory_map + map_offset;
  84                unsigned long slots;
  85
  86                slots = get_entry_num_slots(md, size, ilog2(align));
  87                MD_NUM_SLOTS(md) = slots;
  88                total_slots += slots;
  89        }
  90
  91        /* find a random number between 0 and total_slots */
  92        target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
  93
  94        /*
  95         * target_slot is now a value in the range [0, total_slots), and so
  96         * it corresponds with exactly one of the suitable slots we recorded
  97         * when iterating over the memory map the first time around.
  98         *
  99         * So iterate over the memory map again, subtracting the number of
 100         * slots of each entry at each iteration, until we have found the entry
 101         * that covers our chosen slot. Use the residual value of target_slot
 102         * to calculate the randomly chosen address, and allocate it directly
 103         * using EFI_ALLOCATE_ADDRESS.
 104         */
 105        for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
 106                efi_memory_desc_t *md = (void *)memory_map + map_offset;
 107                efi_physical_addr_t target;
 108                unsigned long pages;
 109
 110                if (target_slot >= MD_NUM_SLOTS(md)) {
 111                        target_slot -= MD_NUM_SLOTS(md);
 112                        continue;
 113                }
 114
 115                target = round_up(md->phys_addr, align) + target_slot * align;
 116                pages = size / EFI_PAGE_SIZE;
 117
 118                status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
 119                                     EFI_LOADER_DATA, pages, &target);
 120                if (status == EFI_SUCCESS)
 121                        *addr = target;
 122                break;
 123        }
 124
 125        efi_bs_call(free_pool, memory_map);
 126
 127        return status;
 128}
 129