[PATCH] efi: stub: call get_memory_map() to obtain map and desc sizes

Ard Biesheuvel
2015-01-08T17:51:47Z

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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
---
drivers/firmware/efi/libstub/efi-stub-helper.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index e766df60fbfb..caf91eab0bfc 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -75,25 +75,29 @@ 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)
--
1.8.3.2