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					 u64 alloc_min, u64 alloc_max)
 21{
 22	unsigned long align = 1UL << align_shift;
 23	u64 first_slot, last_slot, region_end;
 24
 25	if (md->type != EFI_CONVENTIONAL_MEMORY)
 26		return 0;
 27
 28	if (md->attribute & EFI_MEMORY_HOT_PLUGGABLE)
 29		return 0;
 30
 31	if (efi_soft_reserve_enabled() &&
 32	    (md->attribute & EFI_MEMORY_SP))
 33		return 0;
 34
 35	region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1,
 36			 alloc_max);
 37	if (region_end < size)
 38		return 0;
 39
 40	first_slot = round_up(max(md->phys_addr, alloc_min), align);
 41	last_slot = round_down(region_end - size + 1, align);
 42
 43	if (first_slot > last_slot)
 44		return 0;
 45
 46	return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
 47}
 48
 49/*
 50 * The UEFI memory descriptors have a virtual address field that is only used
 51 * when installing the virtual mapping using SetVirtualAddressMap(). Since it
 52 * is unused here, we can reuse it to keep track of each descriptor's slot
 53 * count.
 54 */
 55#define MD_NUM_SLOTS(md)	((md)->virt_addr)
 56
 57efi_status_t efi_random_alloc(unsigned long size,
 58			      unsigned long align,
 59			      unsigned long *addr,
 60			      unsigned long random_seed,
 61			      int memory_type,
 62			      unsigned long alloc_min,
 63			      unsigned long alloc_max)
 64{
 65	struct efi_boot_memmap *map __free(efi_pool) = NULL;
 66	unsigned long total_slots = 0, target_slot;
 67	unsigned long total_mirrored_slots = 0;
 68	efi_status_t status;
 69	int map_offset;
 70
 71	status = efi_get_memory_map(&map, false);
 72	if (status != EFI_SUCCESS)
 73		return status;
 74
 75	if (align < EFI_ALLOC_ALIGN)
 76		align = EFI_ALLOC_ALIGN;
 77
 78	/* Avoid address 0x0, as it can be mistaken for NULL */
 79	if (alloc_min == 0)
 80		alloc_min = align;
 81
 82	size = round_up(size, EFI_ALLOC_ALIGN);
 83
 84	/* count the suitable slots in each memory map entry */
 85	for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
 86		efi_memory_desc_t *md = (void *)map->map + map_offset;
 87		unsigned long slots;
 88
 89		slots = get_entry_num_slots(md, size, ilog2(align), alloc_min,
 90					    alloc_max);
 91		MD_NUM_SLOTS(md) = slots;
 92		total_slots += slots;
 93		if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
 94			total_mirrored_slots += slots;
 95	}
 96
 97	/* consider only mirrored slots for randomization if any exist */
 98	if (total_mirrored_slots > 0)
 99		total_slots = total_mirrored_slots;
100
101	/* find a random number between 0 and total_slots */
102	target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
103
104	/*
105	 * target_slot is now a value in the range [0, total_slots), and so
106	 * it corresponds with exactly one of the suitable slots we recorded
107	 * when iterating over the memory map the first time around.
108	 *
109	 * So iterate over the memory map again, subtracting the number of
110	 * slots of each entry at each iteration, until we have found the entry
111	 * that covers our chosen slot. Use the residual value of target_slot
112	 * to calculate the randomly chosen address, and allocate it directly
113	 * using EFI_ALLOCATE_ADDRESS.
114	 */
115	status = EFI_OUT_OF_RESOURCES;
116	for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
117		efi_memory_desc_t *md = (void *)map->map + map_offset;
118		efi_physical_addr_t target;
119		unsigned long pages;
120
121		if (total_mirrored_slots > 0 &&
122		    !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
123			continue;
124
125		if (target_slot >= MD_NUM_SLOTS(md)) {
126			target_slot -= MD_NUM_SLOTS(md);
127			continue;
128		}
129
130		target = round_up(max_t(u64, md->phys_addr, alloc_min), align) + target_slot * align;
131		pages = size / EFI_PAGE_SIZE;
132
133		status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
134				     memory_type, pages, &target);
135		if (status == EFI_SUCCESS)
136			*addr = target;
137		break;
138	}
139
140	return status;
141}