[PATCH 05/12] efi: libstub: avoid efi_get_memory_map() for allocating the virt map

[Ard Biesheuvel <ardb@kernel.org>]

The virt map is a set of efi_memory_desc_t descriptors that are passed
to SetVirtualAddressMap() to inform the firmware about the desired
virtual mapping of the regions marked as EFI_MEMORY_RUNTIME. The only
reason we currently call the efi_get_memory_map() helper is that it
gives us an allocation that is guaranteed to be of sufficient size.
However, efi_get_memory_map() has grown some additional complexity over
the years, and today, we're actually better off calling the EFI boot
service directly with a zero size, which tells us how much memory should
be enough for the virt map.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/libstub/efi-stub.c | 31 ++++++++++++++++++++
 drivers/firmware/efi/libstub/efistub.h  |  2 ++
 drivers/firmware/efi/libstub/fdt.c      | 27 +++++------------
 3 files changed, 41 insertions(+), 19 deletions(-)

diff --git a/drivers/firmware/efi/libstub/efi-stub.c b/drivers/firmware/efi/libstub/efi-stub.c
index 97eaa487fdfd..6d9ce2c89576 100644
--- a/drivers/firmware/efi/libstub/efi-stub.c
+++ b/drivers/firmware/efi/libstub/efi-stub.c
@@ -319,6 +319,35 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
 	return status;
 }
 
+/*
+ * efi_allocate_virtmap() - create a pool allocation for the virtmap
+ *
+ * Create an allocation that is of sufficient size to hold all the memory
+ * descriptors that will be passed to SetVirtualAddressMap() to inform the
+ * firmware about the virtual mapping that will be used under the OS to call
+ * into the firmware.
+ */
+efi_status_t efi_alloc_virtmap(efi_memory_desc_t **virtmap,
+			       unsigned long *desc_size, u32 *desc_ver)
+{
+	unsigned long size, mmap_key;
+	efi_status_t status;
+
+	/*
+	 * Use the size of the current memory map as an upper bound for the
+	 * size of the buffer we need to pass to SetVirtualAddressMap() to
+	 * cover all EFI_MEMORY_RUNTIME regions.
+	 */
+	size = 0;
+	status = efi_bs_call(get_memory_map, &size, NULL, &mmap_key, desc_size,
+			     desc_ver);
+	if (status != EFI_BUFFER_TOO_SMALL)
+		return EFI_LOAD_ERROR;
+
+	return efi_bs_call(allocate_pool, EFI_LOADER_DATA, size,
+			   (void **)virtmap);
+}
+
 /*
  * efi_get_virtmap() - create a virtual mapping for the EFI memory map
  *
@@ -334,6 +363,8 @@ void efi_get_virtmap(efi_memory_desc_t *memory_map, unsigned long map_size,
 	efi_memory_desc_t *in, *out = runtime_map;
 	int l;
 
+	*count = 0;
+
 	for (l = 0; l < map_size; l += desc_size) {
 		u64 paddr, size;
 
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index 02fb5f7c8eff..20705712deff 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -885,6 +885,8 @@ efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
 
 void *get_fdt(unsigned long *fdt_size);
 
+efi_status_t efi_alloc_virtmap(efi_memory_desc_t **virtmap,
+			       unsigned long *desc_size, u32 *desc_ver);
 void efi_get_virtmap(efi_memory_desc_t *memory_map, unsigned long map_size,
 		     unsigned long desc_size, efi_memory_desc_t *runtime_map,
 		     int *count);
diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
index 804f542be3f2..ab59889c38f1 100644
--- a/drivers/firmware/efi/libstub/fdt.c
+++ b/drivers/firmware/efi/libstub/fdt.c
@@ -199,7 +199,7 @@ static efi_status_t update_fdt_memmap(void *fdt, struct efi_boot_memmap *map)
 
 struct exit_boot_struct {
 	efi_memory_desc_t	*runtime_map;
-	int			*runtime_entry_count;
+	int			runtime_entry_count;
 	void			*new_fdt_addr;
 };
 
@@ -213,7 +213,7 @@ static efi_status_t exit_boot_func(struct efi_boot_memmap *map,
 	 * entries so that we can pass it straight to SetVirtualAddressMap()
 	 */
 	efi_get_virtmap(*map->map, *map->map_size, *map->desc_size,
-			p->runtime_map, p->runtime_entry_count);
+			p->runtime_map, &p->runtime_entry_count);
 
 	return update_fdt_memmap(p->new_fdt_addr, map);
 }
@@ -246,26 +246,18 @@ efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
 	unsigned long map_size, desc_size, buff_size;
 	u32 desc_ver;
 	unsigned long mmap_key;
-	efi_memory_desc_t *memory_map, *runtime_map;
+	efi_memory_desc_t *memory_map;
 	efi_status_t status;
-	int runtime_entry_count;
 	struct efi_boot_memmap map;
 	struct exit_boot_struct priv;
 
-	map.map		= &runtime_map;
 	map.map_size	= &map_size;
 	map.desc_size	= &desc_size;
 	map.desc_ver	= &desc_ver;
 	map.key_ptr	= &mmap_key;
 	map.buff_size	= &buff_size;
 
-	/*
-	 * Get a copy of the current memory map that we will use to prepare
-	 * the input for SetVirtualAddressMap(). We don't have to worry about
-	 * subsequent allocations adding entries, since they could not affect
-	 * the number of EFI_MEMORY_RUNTIME regions.
-	 */
-	status = efi_get_memory_map(&map);
+	status = efi_alloc_virtmap(&priv.runtime_map, &desc_size, &desc_ver);
 	if (status != EFI_SUCCESS) {
 		efi_err("Unable to retrieve UEFI memory map.\n");
 		return status;
@@ -289,10 +281,7 @@ efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
 		goto fail_free_new_fdt;
 	}
 
-	runtime_entry_count		= 0;
-	priv.runtime_map		= runtime_map;
-	priv.runtime_entry_count	= &runtime_entry_count;
-	priv.new_fdt_addr		= (void *)*new_fdt_addr;
+	priv.new_fdt_addr = (void *)*new_fdt_addr;
 
 	status = efi_exit_boot_services(handle, &map, &priv, exit_boot_func);
 
@@ -304,8 +293,8 @@ efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
 
 		/* Install the new virtual address map */
 		svam = efi_system_table->runtime->set_virtual_address_map;
-		status = svam(runtime_entry_count * desc_size, desc_size,
-			      desc_ver, runtime_map);
+		status = svam(priv.runtime_entry_count * desc_size, desc_size,
+			      desc_ver, priv.runtime_map);
 
 		/*
 		 * We are beyond the point of no return here, so if the call to
@@ -337,7 +326,7 @@ efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
 	efi_free(MAX_FDT_SIZE, *new_fdt_addr);
 
 fail:
-	efi_system_table->boottime->free_pool(runtime_map);
+	efi_bs_call(free_pool, priv.runtime_map);
 
 	return EFI_LOAD_ERROR;
 }
-- 
2.35.1