Commit d1a8d66b authored Jan 08, 2015 by Ard Biesheuvel Committed by Matt Fleming Jan 20, 2015

efi/libstub: Call get_memory_map() to obtain map and desc sizes



This fixes two minor issues in the implementation of get_memory_map():
- Currently, it assumes that sizeof(efi_memory_desc_t) == desc_size,
  which is usually true, but not mandated by the spec. (This was added
  intentionally to allow future additions to the definition of
  efi_memory_desc_t). The way the loop is implemented currently, the
  added slack space may be insufficient if desc_size is larger, which in
  some corner cases could result in the loop never terminating.
- It allocates 32 efi_memory_desc_t entries first (again, using the size
  of the struct instead of desc_size), and frees and reallocates if it
  turns out to be insufficient. Few implementations of UEFI have such small
  memory maps, which results in a unnecessary allocate/free pair on each
  invocation.

Fix this by calling the get_memory_map() boot service first with a '0'
input value for map size to retrieve the map size and desc size from the
firmware and only then perform the allocation, using desc_size rather
than sizeof(efi_memory_desc_t).

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

parent 86d68a58

drivers/firmware/efi/libstub/efi-stub-helper.c

+10 −6

Original line number	Diff line number	Diff line
		@@ -66,25 +66,29 @@ efi_status_t efi_get_memory_map(efi_system_table_t *sys_table_arg,
		unsigned long key;
		u32 desc_version;

		map_size = sizeof(m) * 32;
		again:
		*map_size = 0;
		*desc_size = 0;
		key = 0;
		status = efi_call_early(get_memory_map, map_size, NULL,
		&key, desc_size, &desc_version);
		if (status != EFI_BUFFER_TOO_SMALL)
		return EFI_LOAD_ERROR;

		/*
		* Add an additional efi_memory_desc_t because we're doing an
		* allocation which may be in a new descriptor region.
		*/
		map_size += sizeof(m);
		map_size += desc_size;
		status = efi_call_early(allocate_pool, EFI_LOADER_DATA,
		map_size, (void *)&m);
		if (status != EFI_SUCCESS)
		goto fail;

		*desc_size = 0;
		key = 0;
		status = efi_call_early(get_memory_map, map_size, m,
		&key, desc_size, &desc_version);
		if (status == EFI_BUFFER_TOO_SMALL) {
		efi_call_early(free_pool, m);
		goto again;
		return EFI_LOAD_ERROR;
		}

		if (status != EFI_SUCCESS)