efi/x86: Use correct size for boot_params

struct boot_params is only 4096 bytes, not 16384. Fix this by using
sizeof(struct boot_params) instead of hardcoding the incorrect value.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200430182843.2510180-2-nivedita@alum.mit.eduSigned-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/x86-stub.c

@@ -379,13 +379,14 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
 	image_base = efi_table_attr(image, image_base);
 	image_offset = (void *)startup_32 - image_base;
 
-	status = efi_allocate_pages(0x4000, (unsigned long *)&boot_params, ULONG_MAX);
+	status = efi_allocate_pages(sizeof(struct boot_params),
+				    (unsigned long *)&boot_params, ULONG_MAX);
 	if (status != EFI_SUCCESS) {
 		efi_printk("Failed to allocate lowmem for boot params\n");
 		efi_exit(handle, status);
 	}
 
-	memset(boot_params, 0x0, 0x4000);
+	memset(boot_params, 0x0, sizeof(struct boot_params));
 
 	hdr = &boot_params->hdr;
 
@@ -439,7 +440,7 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
 fail2:
 	efi_free(options_size, (unsigned long)cmdline_ptr);
 fail:
-	efi_free(0x4000, (unsigned long)boot_params);
+	efi_free(sizeof(struct boot_params), (unsigned long)boot_params);
 
 	efi_exit(handle, status);
 }