// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org>
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*/
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#include <linux/efi.h>
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#include <linux/log2.h>
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#include <asm/efi.h>
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#include "efistub.h"
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/*
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* Return the number of slots covered by this entry, i.e., the number of
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* addresses it covers that are suitably aligned and supply enough room
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* for the allocation.
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*/
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static unsigned long get_entry_num_slots(efi_memory_desc_t *md,
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unsigned long size,
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unsigned long align_shift)
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{
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unsigned long align = 1UL << align_shift;
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u64 first_slot, last_slot, region_end;
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if (md->type != EFI_CONVENTIONAL_MEMORY)
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return 0;
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if (efi_soft_reserve_enabled() &&
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(md->attribute & EFI_MEMORY_SP))
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return 0;
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region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1,
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(u64)ULONG_MAX);
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if (region_end < size)
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return 0;
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first_slot = round_up(md->phys_addr, align);
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last_slot = round_down(region_end - size + 1, align);
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if (first_slot > last_slot)
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return 0;
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return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
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}
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/*
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* The UEFI memory descriptors have a virtual address field that is only used
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* when installing the virtual mapping using SetVirtualAddressMap(). Since it
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* is unused here, we can reuse it to keep track of each descriptor's slot
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* count.
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*/
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#define MD_NUM_SLOTS(md) ((md)->virt_addr)
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efi_status_t efi_random_alloc(unsigned long size,
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unsigned long align,
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unsigned long *addr,
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unsigned long random_seed)
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{
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unsigned long map_size, desc_size, total_slots = 0, target_slot;
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unsigned long buff_size;
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efi_status_t status;
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efi_memory_desc_t *memory_map;
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int map_offset;
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struct efi_boot_memmap map;
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map.map = &memory_map;
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map.map_size = &map_size;
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map.desc_size = &desc_size;
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map.desc_ver = NULL;
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map.key_ptr = NULL;
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map.buff_size = &buff_size;
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status = efi_get_memory_map(&map);
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if (status != EFI_SUCCESS)
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return status;
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if (align < EFI_ALLOC_ALIGN)
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align = EFI_ALLOC_ALIGN;
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size = round_up(size, EFI_ALLOC_ALIGN);
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/* count the suitable slots in each memory map entry */
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for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
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efi_memory_desc_t *md = (void *)memory_map + map_offset;
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unsigned long slots;
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slots = get_entry_num_slots(md, size, ilog2(align));
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MD_NUM_SLOTS(md) = slots;
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total_slots += slots;
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}
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/* find a random number between 0 and total_slots */
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target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
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/*
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* target_slot is now a value in the range [0, total_slots), and so
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* it corresponds with exactly one of the suitable slots we recorded
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* when iterating over the memory map the first time around.
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*
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* So iterate over the memory map again, subtracting the number of
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* slots of each entry at each iteration, until we have found the entry
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* that covers our chosen slot. Use the residual value of target_slot
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* to calculate the randomly chosen address, and allocate it directly
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* using EFI_ALLOCATE_ADDRESS.
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*/
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for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
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efi_memory_desc_t *md = (void *)memory_map + map_offset;
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efi_physical_addr_t target;
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unsigned long pages;
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if (target_slot >= MD_NUM_SLOTS(md)) {
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target_slot -= MD_NUM_SLOTS(md);
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continue;
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}
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target = round_up(md->phys_addr, align) + target_slot * align;
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pages = size / EFI_PAGE_SIZE;
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status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
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EFI_LOADER_DATA, pages, &target);
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if (status == EFI_SUCCESS)
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*addr = target;
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break;
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}
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efi_bs_call(free_pool, memory_map);
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return status;
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}
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