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efi/libstub: Move efi_random_alloc() into separate source file
efi_random_alloc() is only used on arm64, but as it shares a source file with efi_random_get_seed(), the latter will pull in the former on other architectures as well. Let's take advantage of the fact that libstub is a static library, and so the linker will only incorporate objects that are needed to satisfy dependencies in other objects. This means we can move the random alloc code to a separate source file that gets built unconditionally, but only used when needed. Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
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Ard Biesheuvel
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Feb 23, 2020
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,124 @@ | ||
| // SPDX-License-Identifier: GPL-2.0 | ||
| /* | ||
| * Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org> | ||
| */ | ||
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| #include <linux/efi.h> | ||
| #include <linux/log2.h> | ||
| #include <asm/efi.h> | ||
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| #include "efistub.h" | ||
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| /* | ||
| * 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; | ||
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| if (md->type != EFI_CONVENTIONAL_MEMORY) | ||
| return 0; | ||
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| if (efi_soft_reserve_enabled() && | ||
| (md->attribute & EFI_MEMORY_SP)) | ||
| return 0; | ||
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| region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1, | ||
| (u64)ULONG_MAX); | ||
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| first_slot = round_up(md->phys_addr, align); | ||
| last_slot = round_down(region_end - size + 1, align); | ||
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| if (first_slot > last_slot) | ||
| return 0; | ||
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| return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1; | ||
| } | ||
|
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| /* | ||
| * 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) | ||
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| efi_status_t efi_random_alloc(unsigned long size, | ||
| unsigned long align, | ||
| unsigned long *addr, | ||
| unsigned long random_seed) | ||
| { | ||
| unsigned long map_size, desc_size, total_slots = 0, target_slot; | ||
| unsigned long buff_size; | ||
| efi_status_t status; | ||
| efi_memory_desc_t *memory_map; | ||
| int map_offset; | ||
| struct efi_boot_memmap map; | ||
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| map.map = &memory_map; | ||
| map.map_size = &map_size; | ||
| map.desc_size = &desc_size; | ||
| map.desc_ver = NULL; | ||
| map.key_ptr = NULL; | ||
| map.buff_size = &buff_size; | ||
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| status = efi_get_memory_map(&map); | ||
| if (status != EFI_SUCCESS) | ||
| return status; | ||
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| if (align < EFI_ALLOC_ALIGN) | ||
| align = EFI_ALLOC_ALIGN; | ||
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| /* 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; | ||
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| slots = get_entry_num_slots(md, size, ilog2(align)); | ||
| MD_NUM_SLOTS(md) = slots; | ||
| total_slots += slots; | ||
| } | ||
|
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| /* find a random number between 0 and total_slots */ | ||
| target_slot = (total_slots * (u16)random_seed) >> 16; | ||
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| /* | ||
| * 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; | ||
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| if (target_slot >= MD_NUM_SLOTS(md)) { | ||
| target_slot -= MD_NUM_SLOTS(md); | ||
| continue; | ||
| } | ||
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| target = round_up(md->phys_addr, align) + target_slot * align; | ||
| pages = round_up(size, EFI_PAGE_SIZE) / EFI_PAGE_SIZE; | ||
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| status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS, | ||
| EFI_LOADER_DATA, pages, &target); | ||
| if (status == EFI_SUCCESS) | ||
| *addr = target; | ||
| break; | ||
| } | ||
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| efi_bs_call(free_pool, memory_map); | ||
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| return status; | ||
| } |