[PATCH] efi: get_memory_map: add sufficient slack for memory descriptors

[Ard Biesheuvel]

As it turns out, when allocating room for the UEFI memory map using
UEFI's AllocatePool (), it may result in two new memory map entries
being created, for instance, when using Tianocore's preallocated region
feature. For example, the following region

0x00005ead5000-0x00005ebfffff [Conventional Memory|   |  |  |  |   |WB|WT|WC|UC]

may be split like this

0x00005ead5000-0x00005eae2fff [Conventional Memory|   |  |  |  |   |WB|WT|WC|UC]
0x00005eae3000-0x00005eae4fff [Loader Data        |   |  |  |  |   |WB|WT|WC|UC]
0x00005eae5000-0x00005ebfffff [Conventional Memory|   |  |  |  |   |WB|WT|WC|UC]

if the preallocated Loader Data region was chosen to be right in the
middle of the original free space.

After patch d1a8d66b9177 ("efi/libstub: Call get_memory_map() to
obtain map and desc sizes"), this is not being dealt with correctly
anymore, as the existing logic to allocate room for a single additional
entry has become insufficient.

So instead, add room for two additional entries instead.

Fixes: d1a8d66b9177 ("efi/libstub: Call get_memory_map() to obtain map and desc sizes")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 drivers/firmware/efi/libstub/efi-stub-helper.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index af5d63c7cc53..ca0b07ed3b14 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -84,10 +84,10 @@ efi_status_t efi_get_memory_map(efi_system_table_t *sys_table_arg,
 		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.
+	 * Add room for two additional efi_memory_desc_t entries because we're
+	 * doing an allocation which may be in a new descriptor region.
 	 */
-	*map_size += *desc_size;
+	*map_size += *desc_size * 2;
 	status = efi_call_early(allocate_pool, EFI_LOADER_DATA,
 				*map_size, (void **)&m);
 	if (status != EFI_SUCCESS)
-- 
1.8.3.2