efi: stub: implement efi_get_random_bytes() based on EFI_RNG_PROTOCOL

This exposes the firmware's implementation of EFI_RNG_PROTOCOL via a new
function efi_get_random_bytes().

Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

drivers/firmware/efi/libstub/Makefile

@@ -36,7 +36,7 @@ lib-$(CONFIG_EFI_ARMSTUB)	+= arm-stub.o fdt.o string.o \
 				   $(patsubst %.c,lib-%.o,$(arm-deps))
 
 lib-$(CONFIG_ARM)		+= arm32-stub.o
-lib-$(CONFIG_ARM64)		+= arm64-stub.o
+lib-$(CONFIG_ARM64)		+= arm64-stub.o random.o
 CFLAGS_arm64-stub.o 		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 
 #

drivers/firmware/efi/libstub/efistub.h

@@ -43,4 +43,7 @@ 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);
 
+efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table,
+				  unsigned long size, u8 *out);
+
 #endif

drivers/firmware/efi/libstub/random.c

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/efi.h>
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+struct efi_rng_protocol {
+	efi_status_t (*get_info)(struct efi_rng_protocol *,
+				 unsigned long *, efi_guid_t *);
+	efi_status_t (*get_rng)(struct efi_rng_protocol *,
+				efi_guid_t *, unsigned long, u8 *out);
+};
+
+efi_status_t efi_get_random_bytes(efi_system_table_t *sys_table_arg,
+				  unsigned long size, u8 *out)
+{
+	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
+	efi_status_t status;
+	struct efi_rng_protocol *rng;
+
+	status = efi_call_early(locate_protocol, &rng_proto, NULL,
+				(void **)&rng);
+	if (status != EFI_SUCCESS)
+		return status;
+
+	return rng->get_rng(rng, NULL, size, out);
+}

include/linux/efi.h

@@ -299,7 +299,7 @@ typedef struct {
 	void *open_protocol_information;
 	void *protocols_per_handle;
 	void *locate_handle_buffer;
-	void *locate_protocol;
+	efi_status_t (*locate_protocol)(efi_guid_t *, void *, void **);
 	void *install_multiple_protocol_interfaces;
 	void *uninstall_multiple_protocol_interfaces;
 	void *calculate_crc32;
@@ -599,6 +599,10 @@ void efi_native_runtime_setup(void);
 #define EFI_PROPERTIES_TABLE_GUID \
     EFI_GUID(  0x880aaca3, 0x4adc, 0x4a04, 0x90, 0x79, 0xb7, 0x47, 0x34, 0x08, 0x25, 0xe5 )
 
+#define EFI_RNG_PROTOCOL_GUID \
+	EFI_GUID(0x3152bca5, 0xeade, 0x433d, \
+		 0x86, 0x2e, 0xc0, 0x1c, 0xdc, 0x29, 0x1f, 0x44)
+
 typedef struct {
 	efi_guid_t guid;
 	u64 table;