@@ -46,4 +46,8 @@ void efi_get_virtmap(efi_memory_desc_t *memory_map, unsigned long map_size,
efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table,
unsigned long size, u8 *out);
+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);
+
#endif
@@ -33,3 +33,103 @@ efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
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;
+}