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}