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Subject[tip: efi/urgent] efi/libstub/x86: Avoid EFI map buffer alloc in allocate_e820()
The following commit has been merged into the efi/urgent branch of tip:

Commit-ID: fd62619598069c974739476d1851a00d665041d7
Gitweb: https://git.kernel.org/tip/fd62619598069c974739476d1851a00d665041d7
Author: Lenny Szubowicz <lszubowi@redhat.com>
AuthorDate: Thu, 07 May 2020 14:33:32 -04:00
Committer: Ard Biesheuvel <ardb@kernel.org>
CommitterDate: Thu, 14 May 2020 11:11:18 +02:00

efi/libstub/x86: Avoid EFI map buffer alloc in allocate_e820()

In allocate_e820(), call the EFI get_memory_map() service directly
instead of indirectly via efi_get_memory_map(). This avoids allocation
of a buffer and return of the full EFI memory map, which is not needed
here and would otherwise need to be freed.

Routine allocate_e820() only needs to know how many EFI memory
descriptors there are in the map to allocate an adequately sized
e820ext buffer, if it's needed. Note that since efi_get_memory_map()
returns a memory map buffer sized with extra headroom, allocate_e820()
now needs to explicitly factor that into the e820ext size calculation.

Signed-off-by: Lenny Szubowicz <lszubowi@redhat.com>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
drivers/firmware/efi/libstub/efistub.h | 13 +++++++++++++-
drivers/firmware/efi/libstub/mem.c | 2 +--
drivers/firmware/efi/libstub/x86-stub.c | 24 +++++++++---------------
3 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index 67d2694..6294399 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -92,6 +92,19 @@ extern __pure efi_system_table_t *efi_system_table(void);
#define EFI_LOCATE_BY_REGISTER_NOTIFY 1
#define EFI_LOCATE_BY_PROTOCOL 2

+/*
+ * An efi_boot_memmap is used by efi_get_memory_map() to return the
+ * EFI memory map in a dynamically allocated buffer.
+ *
+ * The buffer allocated for the EFI memory map includes extra room for
+ * a minimum of EFI_MMAP_NR_SLACK_SLOTS additional EFI memory descriptors.
+ * This facilitates the reuse of the EFI memory map buffer when a second
+ * call to ExitBootServices() is needed because of intervening changes to
+ * the EFI memory map. Other related structures, e.g. x86 e820ext, need
+ * to factor in this headroom requirement as well.
+ */
+#define EFI_MMAP_NR_SLACK_SLOTS 8
+
struct efi_boot_memmap {
efi_memory_desc_t **map;
unsigned long *map_size;
diff --git a/drivers/firmware/efi/libstub/mem.c b/drivers/firmware/efi/libstub/mem.c
index 869a79c..09f4fa0 100644
--- a/drivers/firmware/efi/libstub/mem.c
+++ b/drivers/firmware/efi/libstub/mem.c
@@ -5,8 +5,6 @@

#include "efistub.h"

-#define EFI_MMAP_NR_SLACK_SLOTS 8
-
static inline bool mmap_has_headroom(unsigned long buff_size,
unsigned long map_size,
unsigned long desc_size)
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 05ccb22..f0339b5 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -606,24 +606,18 @@ static efi_status_t allocate_e820(struct boot_params *params,
struct setup_data **e820ext,
u32 *e820ext_size)
{
- unsigned long map_size, desc_size, buff_size;
- struct efi_boot_memmap boot_map;
- efi_memory_desc_t *map;
+ unsigned long map_size, desc_size, map_key;
efi_status_t status;
- __u32 nr_desc;
+ __u32 nr_desc, desc_version;

- boot_map.map = &map;
- boot_map.map_size = &map_size;
- boot_map.desc_size = &desc_size;
- boot_map.desc_ver = NULL;
- boot_map.key_ptr = NULL;
- boot_map.buff_size = &buff_size;
+ /* Only need the size of the mem map and size of each mem descriptor */
+ map_size = 0;
+ status = efi_bs_call(get_memory_map, &map_size, NULL, &map_key,
+ &desc_size, &desc_version);
+ if (status != EFI_BUFFER_TOO_SMALL)
+ return (status != EFI_SUCCESS) ? status : EFI_UNSUPPORTED;

- status = efi_get_memory_map(&boot_map);
- if (status != EFI_SUCCESS)
- return status;
-
- nr_desc = buff_size / desc_size;
+ nr_desc = map_size / desc_size + EFI_MMAP_NR_SLACK_SLOTS;

if (nr_desc > ARRAY_SIZE(params->e820_table)) {
u32 nr_e820ext = nr_desc - ARRAY_SIZE(params->e820_table);
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