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a6cfe03c34
If the system exposes memory regions with the EFI_MORE_RELIABLE attribute, it is implied that it is intended to be used for allocations that are relatively important, such as the kernel's static image. Since efi_random_alloc() is mostly (only) used for allocating space for the kernel image, let's update it to take this into account, and disregard all memory without the EFI_MORE_RELIABLE attribute if there is sufficient memory available that does have this attribute. Note that this change only affects booting with randomization enabled. In other cases, the EFI stub runs the kernel image in place unless its placement is unsuitable for some reason (i.e., misaligned, or its BSS overlaps with another allocation), and it is left to the bootloader to ensure that the kernel was loaded into EFI_MORE_RELIABLE memory if this is desired. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
139 lines
3.9 KiB
C
139 lines
3.9 KiB
C
// 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 total_mirrored_slots = 0;
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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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if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
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total_mirrored_slots += slots;
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}
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/* consider only mirrored slots for randomization if any exist */
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if (total_mirrored_slots > 0)
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total_slots = total_mirrored_slots;
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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 (total_mirrored_slots > 0 &&
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!(md->attribute & EFI_MEMORY_MORE_RELIABLE))
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continue;
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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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