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/*
* Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
*/
#include <linux/efi.h>
#include <asm/efi.h>
#include "efistub.h"
struct efi_rng_protocol {
efi_status_t (*get_info)(struct efi_rng_protocol *,
unsigned long *, efi_guid_t *);
efi_status_t (*get_rng)(struct efi_rng_protocol *,
efi_guid_t *, unsigned long, u8 *out);
};
efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
unsigned long size, u8 *out)
{
efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
efi_status_t status;
struct efi_rng_protocol *rng;
status = efi_call_early(locate_protocol, &rng_proto, NULL,
(void **)&rng);
if (status != EFI_SUCCESS)
return status;
return rng->get_rng(rng, NULL, size, out);
}
/*
* 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)
{
u64 start, end;
if (md->type != EFI_CONVENTIONAL_MEMORY)
return 0;
start = round_up(md->phys_addr, align);
end = round_down(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - size,
align);
if (start > end)
return 0;
return (end - start + 1) / align;
}
/*
* 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(efi_system_table_t *sys_table_arg,
unsigned long size,
unsigned long align,
unsigned long *addr,
unsigned long random_seed)
{
unsigned long map_size, desc_size, total_slots = 0, target_slot;
efi_status_t status;
efi_memory_desc_t *memory_map;
int map_offset;
status = efi_get_memory_map(sys_table_arg, &memory_map, &map_size,
&desc_size, NULL, NULL);
if (status != EFI_SUCCESS)
return status;
if (align < EFI_ALLOC_ALIGN)
align = EFI_ALLOC_ALIGN;
/* count the suitable slots in each memory map entry */
for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
efi_memory_desc_t *md = (void *)memory_map + map_offset;
unsigned long slots;
slots = get_entry_num_slots(md, size, align);
MD_NUM_SLOTS(md) = slots;
total_slots += slots;
}
/* find a random number between 0 and total_slots */
target_slot = (total_slots * (u16)random_seed) >> 16;
/*
* 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_size; map_offset += desc_size) {
efi_memory_desc_t *md = (void *)memory_map + map_offset;
efi_physical_addr_t target;
unsigned long pages;
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 = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE;
status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
EFI_LOADER_DATA, pages, &target);
if (status == EFI_SUCCESS)
*addr = target;
break;
}
efi_call_early(free_pool, memory_map);
return status;
}
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