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