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
  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
  51efi_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 * (u64)(random_seed & U32_MAX)) >> 32;
  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}
 127