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-rw-r--r--drivers/firmware/efi/libstub/randomalloc.c130
1 files changed, 130 insertions, 0 deletions
diff --git a/drivers/firmware/efi/libstub/randomalloc.c b/drivers/firmware/efi/libstub/randomalloc.c
new file mode 100644
index 000000000..9fb586989
--- /dev/null
+++ b/drivers/firmware/efi/libstub/randomalloc.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org>
+ */
+
+#include <linux/efi.h>
+#include <linux/log2.h>
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+/*
+ * 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;
+
+ if (md->type != EFI_CONVENTIONAL_MEMORY)
+ return 0;
+
+ if (efi_soft_reserve_enabled() &&
+ (md->attribute & EFI_MEMORY_SP))
+ return 0;
+
+ region_end = min(md->phys_addr + md->num_pages * EFI_PAGE_SIZE - 1,
+ (u64)ULONG_MAX);
+ if (region_end < size)
+ return 0;
+
+ first_slot = round_up(md->phys_addr, align);
+ last_slot = round_down(region_end - size + 1, align);
+
+ if (first_slot > last_slot)
+ return 0;
+
+ return ((unsigned long)(last_slot - first_slot) >> align_shift) + 1;
+}
+
+/*
+ * 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(unsigned long size,
+ unsigned long align,
+ unsigned long *addr,
+ unsigned long random_seed)
+{
+ unsigned long total_slots = 0, target_slot;
+ unsigned long total_mirrored_slots = 0;
+ struct efi_boot_memmap *map;
+ efi_status_t status;
+ int map_offset;
+
+ status = efi_get_memory_map(&map, false);
+ if (status != EFI_SUCCESS)
+ return status;
+
+ if (align < EFI_ALLOC_ALIGN)
+ align = EFI_ALLOC_ALIGN;
+
+ size = round_up(size, EFI_ALLOC_ALIGN);
+
+ /* count the suitable slots in each memory map entry */
+ for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
+ efi_memory_desc_t *md = (void *)map->map + map_offset;
+ unsigned long slots;
+
+ slots = get_entry_num_slots(md, size, ilog2(align));
+ MD_NUM_SLOTS(md) = slots;
+ total_slots += slots;
+ if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
+ total_mirrored_slots += slots;
+ }
+
+ /* consider only mirrored slots for randomization if any exist */
+ if (total_mirrored_slots > 0)
+ total_slots = total_mirrored_slots;
+
+ /* find a random number between 0 and total_slots */
+ target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
+
+ /*
+ * 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->map_size; map_offset += map->desc_size) {
+ efi_memory_desc_t *md = (void *)map->map + map_offset;
+ efi_physical_addr_t target;
+ unsigned long pages;
+
+ if (total_mirrored_slots > 0 &&
+ !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
+ continue;
+
+ 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 = size / EFI_PAGE_SIZE;
+
+ status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
+ EFI_LOADER_DATA, pages, &target);
+ if (status == EFI_SUCCESS)
+ *addr = target;
+ break;
+ }
+
+ efi_bs_call(free_pool, map);
+
+ return status;
+}