efi_loader: Implement EFI variable handling via OP-TEE
authorIlias Apalodimas <ilias.apalodimas@linaro.org>
Sun, 17 May 2020 19:25:44 +0000 (22:25 +0300)
committerHeinrich Schuchardt <xypron.glpk@gmx.de>
Sun, 17 May 2020 19:59:53 +0000 (21:59 +0200)
In OP-TEE we can run EDK2's StandAloneMM on a secure partition.
StandAloneMM is responsible for the UEFI variable support. In
combination with OP-TEE and it's U-Boot supplicant, variables are
authenticated/validated in secure world and stored on an RPMB partition.

So let's add a new config option in U-Boot implementing the necessary
calls to OP-TEE for the variable management.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Pipat Methavanitpong <pipat1010@gmail.com>
Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
lib/efi_loader/Kconfig
lib/efi_loader/Makefile
lib/efi_loader/efi_variable_tee.c [new file with mode: 0644]

index 1cfa24ffcf727eed1e7aa9bb9794f916423541cf..aad37b715505e3713378d8e8d77cd4f8c009c9e0 100644 (file)
@@ -164,4 +164,13 @@ config EFI_SECURE_BOOT
          it is signed with a trusted key. To do that, you need to install,
          at least, PK, KEK and db.
 
+config EFI_MM_COMM_TEE
+       bool "UEFI variables storage service via OP-TEE"
+       depends on OPTEE
+       default n
+       help
+         If OP-TEE is present and running StandAloneMM, dispatch all UEFI variable
+         related operations to that. The application will verify, authenticate and
+         store the variables on an RPMB.
+
 endif
index 84d61df55b93d89039e561ee4ec6734babf624db..57c7e66ea0e2331e33afdd72d5128a9b7106c2ad 100644 (file)
@@ -35,7 +35,11 @@ obj-y += efi_root_node.o
 obj-y += efi_runtime.o
 obj-y += efi_setup.o
 obj-$(CONFIG_EFI_UNICODE_COLLATION_PROTOCOL2) += efi_unicode_collation.o
+ifeq ($(CONFIG_EFI_MM_COMM_TEE),y)
+obj-y += efi_variable_tee.o
+else
 obj-y += efi_variable.o
+endif
 obj-y += efi_watchdog.o
 obj-$(CONFIG_LCD) += efi_gop.o
 obj-$(CONFIG_DM_VIDEO) += efi_gop.o
diff --git a/lib/efi_loader/efi_variable_tee.c b/lib/efi_loader/efi_variable_tee.c
new file mode 100644 (file)
index 0000000..cacc76e
--- /dev/null
@@ -0,0 +1,662 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ *  EFI variable service via OP-TEE
+ *
+ *  Copyright (C) 2019 Linaro Ltd. <sughosh.ganu@linaro.org>
+ *  Copyright (C) 2019 Linaro Ltd. <ilias.apalodimas@linaro.org>
+ */
+
+#include <common.h>
+#include <efi.h>
+#include <efi_api.h>
+#include <efi_loader.h>
+#include <tee.h>
+#include <malloc.h>
+#include <mm_communication.h>
+
+static efi_uintn_t max_buffer_size;    /* comm + var + func + data */
+static efi_uintn_t max_payload_size;   /* func + data */
+
+struct mm_connection {
+       struct udevice *tee;
+       u32 session;
+};
+
+/**
+ * get_connection() - Retrieve OP-TEE session for a specific UUID.
+ *
+ * @conn:   session buffer to fill
+ * Return:  status code
+ */
+static int get_connection(struct mm_connection *conn)
+{
+       static const struct tee_optee_ta_uuid uuid = PTA_STMM_UUID;
+       struct udevice *tee = NULL;
+       struct tee_open_session_arg arg;
+       int rc;
+
+       tee = tee_find_device(tee, NULL, NULL, NULL);
+       if (!tee)
+               return -ENODEV;
+
+       memset(&arg, 0, sizeof(arg));
+       tee_optee_ta_uuid_to_octets(arg.uuid, &uuid);
+       rc = tee_open_session(tee, &arg, 0, NULL);
+       if (!rc) {
+               conn->tee = tee;
+               conn->session = arg.session;
+       }
+
+       return rc;
+}
+
+/**
+ * optee_mm_communicate() - Pass a buffer to StandaloneMM running in OP-TEE
+ *
+ * @comm_buf:          locally allocted communcation buffer
+ * @dsize:             buffer size
+ * Return:             status code
+ */
+static efi_status_t optee_mm_communicate(void *comm_buf, ulong dsize)
+{
+       ulong buf_size;
+       efi_status_t ret;
+       struct efi_mm_communicate_header *mm_hdr;
+       struct mm_connection conn = { NULL, 0 };
+       struct tee_invoke_arg arg;
+       struct tee_param param[2];
+       struct tee_shm *shm = NULL;
+       int rc;
+
+       if (!comm_buf)
+               return EFI_INVALID_PARAMETER;
+
+       mm_hdr = (struct efi_mm_communicate_header *)comm_buf;
+       buf_size = mm_hdr->message_len + sizeof(efi_guid_t) + sizeof(size_t);
+
+       if (dsize != buf_size)
+               return EFI_INVALID_PARAMETER;
+
+       rc = get_connection(&conn);
+       if (rc) {
+               log_err("Unable to open OP-TEE session (err=%d)\n", rc);
+               return EFI_UNSUPPORTED;
+       }
+
+       if (tee_shm_register(conn.tee, comm_buf, buf_size, 0, &shm)) {
+               log_err("Unable to register shared memory\n");
+               return EFI_UNSUPPORTED;
+       }
+
+       memset(&arg, 0, sizeof(arg));
+       arg.func = PTA_STMM_CMDID_COMMUNICATE;
+       arg.session = conn.session;
+
+       memset(param, 0, sizeof(param));
+       param[0].attr = TEE_PARAM_ATTR_TYPE_MEMREF_INOUT;
+       param[0].u.memref.size = buf_size;
+       param[0].u.memref.shm = shm;
+       param[1].attr = TEE_PARAM_ATTR_TYPE_VALUE_OUTPUT;
+
+       rc = tee_invoke_func(conn.tee, &arg, 2, param);
+       if (rc)
+               return EFI_INVALID_PARAMETER;
+       tee_shm_free(shm);
+       tee_close_session(conn.tee, conn.session);
+
+       switch (param[1].u.value.a) {
+       case ARM_SMC_MM_RET_SUCCESS:
+               ret = EFI_SUCCESS;
+               break;
+
+       case ARM_SMC_MM_RET_INVALID_PARAMS:
+               ret = EFI_INVALID_PARAMETER;
+               break;
+
+       case ARM_SMC_MM_RET_DENIED:
+               ret = EFI_ACCESS_DENIED;
+               break;
+
+       case ARM_SMC_MM_RET_NO_MEMORY:
+               ret = EFI_OUT_OF_RESOURCES;
+               break;
+
+       default:
+               ret = EFI_ACCESS_DENIED;
+       }
+
+       return ret;
+}
+
+/**
+ * mm_communicate() - Adjust the cmonnucation buffer to StandAlonneMM and send
+ * it to OP-TEE
+ *
+ * @comm_buf:          locally allocted communcation buffer
+ * @dsize:             buffer size
+ * Return:             status code
+ */
+static efi_status_t mm_communicate(u8 *comm_buf, efi_uintn_t dsize)
+{
+       efi_status_t ret;
+       struct efi_mm_communicate_header *mm_hdr;
+       struct smm_variable_communicate_header *var_hdr;
+
+       dsize += MM_COMMUNICATE_HEADER_SIZE + MM_VARIABLE_COMMUNICATE_SIZE;
+       mm_hdr = (struct efi_mm_communicate_header *)comm_buf;
+       var_hdr = (struct smm_variable_communicate_header *)mm_hdr->data;
+
+       ret = optee_mm_communicate(comm_buf, dsize);
+       if (ret != EFI_SUCCESS) {
+               log_err("%s failed!\n", __func__);
+               return ret;
+       }
+
+       return var_hdr->ret_status;
+}
+
+/**
+ * setup_mm_hdr() -    Allocate a buffer for StandAloneMM and initialize the
+ *                     header data.
+ *
+ * @dptr:              pointer address of the corresponding StandAloneMM
+ *                     function
+ * @payload_size:      buffer size
+ * @func:              standAloneMM function number
+ * @ret:               EFI return code
+ * Return:             buffer or NULL
+ */
+static u8 *setup_mm_hdr(void **dptr, efi_uintn_t payload_size,
+                       efi_uintn_t func, efi_status_t *ret)
+{
+       const efi_guid_t mm_var_guid = EFI_MM_VARIABLE_GUID;
+       struct efi_mm_communicate_header *mm_hdr;
+       struct smm_variable_communicate_header *var_hdr;
+       u8 *comm_buf;
+
+       /* In the init function we initialize max_buffer_size with
+        * get_max_payload(). So skip the test if max_buffer_size is initialized
+        * StandAloneMM will perform similar checks and drop the buffer if it's
+        * too long
+        */
+       if (max_buffer_size && max_buffer_size <
+                       (MM_COMMUNICATE_HEADER_SIZE +
+                        MM_VARIABLE_COMMUNICATE_SIZE +
+                        payload_size)) {
+               *ret = EFI_INVALID_PARAMETER;
+               return NULL;
+       }
+
+       comm_buf = calloc(1, MM_COMMUNICATE_HEADER_SIZE +
+                         MM_VARIABLE_COMMUNICATE_SIZE +
+                         payload_size);
+       if (!comm_buf) {
+               *ret = EFI_OUT_OF_RESOURCES;
+               return NULL;
+       }
+
+       mm_hdr = (struct efi_mm_communicate_header *)comm_buf;
+       guidcpy(&mm_hdr->header_guid, &mm_var_guid);
+       mm_hdr->message_len = MM_VARIABLE_COMMUNICATE_SIZE + payload_size;
+
+       var_hdr = (struct smm_variable_communicate_header *)mm_hdr->data;
+       var_hdr->function = func;
+       if (dptr)
+               *dptr = var_hdr->data;
+       *ret = EFI_SUCCESS;
+
+       return comm_buf;
+}
+
+/**
+ * get_max_payload() - Get variable payload size from StandAloneMM.
+ *
+ * @size:    size of the variable in storage
+ * Return:   status code
+ */
+efi_status_t EFIAPI get_max_payload(efi_uintn_t *size)
+{
+       struct smm_variable_payload_size *var_payload = NULL;
+       efi_uintn_t payload_size;
+       u8 *comm_buf = NULL;
+       efi_status_t ret;
+
+       if (!size) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+
+       payload_size = sizeof(*var_payload);
+       comm_buf = setup_mm_hdr((void **)&var_payload, payload_size,
+                               SMM_VARIABLE_FUNCTION_GET_PAYLOAD_SIZE, &ret);
+       if (!comm_buf)
+               goto out;
+
+       ret = mm_communicate(comm_buf, payload_size);
+       if (ret != EFI_SUCCESS)
+               goto out;
+
+       *size = var_payload->size;
+
+out:
+       free(comm_buf);
+       return ret;
+}
+
+/**
+ * efi_get_variable() - retrieve value of a UEFI variable
+ *
+ * This function implements the GetVariable runtime service.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * @name:              name of the variable
+ * @guid:              vendor GUID
+ * @attr:              attributes of the variable
+ * @data_size:         size of the buffer to which the variable value is copied
+ * @data:              buffer to which the variable value is copied
+ * Return:             status code
+ */
+efi_status_t EFIAPI efi_get_variable(u16 *name, const efi_guid_t *guid,
+                                    u32 *attr, efi_uintn_t *data_size,
+                                    void *data)
+{
+       struct smm_variable_access *var_acc;
+       efi_uintn_t payload_size;
+       efi_uintn_t name_size;
+       efi_uintn_t tmp_dsize;
+       u8 *comm_buf = NULL;
+       efi_status_t ret;
+
+       EFI_ENTRY("\"%ls\" %pUl %p %p %p", name, guid, attr, data_size, data);
+
+       if (!name || !guid || !data_size) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+
+       /* Check payload size */
+       name_size = u16_strsize(name);
+       if (name_size > max_payload_size - MM_VARIABLE_ACCESS_HEADER_SIZE) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+
+       /* Trim output buffer size */
+       tmp_dsize = *data_size;
+       if (name_size + tmp_dsize >
+                       max_payload_size - MM_VARIABLE_ACCESS_HEADER_SIZE) {
+               tmp_dsize = max_payload_size -
+                               MM_VARIABLE_ACCESS_HEADER_SIZE -
+                               name_size;
+       }
+
+       /* Get communication buffer and initialize header */
+       payload_size = MM_VARIABLE_ACCESS_HEADER_SIZE + name_size + tmp_dsize;
+       comm_buf = setup_mm_hdr((void **)&var_acc, payload_size,
+                               SMM_VARIABLE_FUNCTION_GET_VARIABLE, &ret);
+       if (!comm_buf)
+               goto out;
+
+       /* Fill in contents */
+       guidcpy(&var_acc->guid, guid);
+       var_acc->data_size = tmp_dsize;
+       var_acc->name_size = name_size;
+       var_acc->attr = attr ? *attr : 0;
+       memcpy(var_acc->name, name, name_size);
+
+       /* Communicate */
+       ret = mm_communicate(comm_buf, payload_size);
+       if (ret == EFI_SUCCESS || ret == EFI_BUFFER_TOO_SMALL) {
+               /* Update with reported data size for trimmed case */
+               *data_size = var_acc->data_size;
+       }
+       if (ret != EFI_SUCCESS)
+               goto out;
+
+       if (attr)
+               *attr = var_acc->attr;
+       if (data)
+               memcpy(data, (u8 *)var_acc->name + var_acc->name_size,
+                      var_acc->data_size);
+       else
+               ret = EFI_INVALID_PARAMETER;
+
+out:
+       free(comm_buf);
+       return EFI_EXIT(ret);
+}
+
+/**
+ * efi_get_next_variable_name() - enumerate the current variable names
+ *
+ * @variable_name_size:        size of variable_name buffer in bytes
+ * @variable_name:     name of uefi variable's name in u16
+ * @guid:              vendor's guid
+ *
+ * This function implements the GetNextVariableName service.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * Return: status code
+ */
+efi_status_t EFIAPI efi_get_next_variable_name(efi_uintn_t *variable_name_size,
+                                              u16 *variable_name,
+                                              efi_guid_t *guid)
+{
+       struct smm_variable_getnext *var_getnext;
+       efi_uintn_t payload_size;
+       efi_uintn_t out_name_size;
+       efi_uintn_t in_name_size;
+       efi_uintn_t tmp_dsize;
+       efi_uintn_t name_size;
+       u8 *comm_buf = NULL;
+       efi_status_t ret;
+
+       EFI_ENTRY("%p \"%ls\" %pUl", variable_name_size, variable_name, guid);
+
+       if (!variable_name_size || !variable_name || !guid) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+
+       out_name_size = *variable_name_size;
+       in_name_size = u16_strsize(variable_name);
+
+       if (out_name_size < in_name_size) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+
+       name_size = u16_strsize(variable_name);
+       if (name_size > max_payload_size - MM_VARIABLE_GET_NEXT_HEADER_SIZE) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+
+       /* Trim output buffer size */
+       tmp_dsize = *variable_name_size;
+       if (name_size + tmp_dsize >
+                       max_payload_size - MM_VARIABLE_GET_NEXT_HEADER_SIZE) {
+               tmp_dsize = max_payload_size -
+                               MM_VARIABLE_GET_NEXT_HEADER_SIZE -
+                               name_size;
+       }
+
+       payload_size = MM_VARIABLE_GET_NEXT_HEADER_SIZE + out_name_size;
+       comm_buf = setup_mm_hdr((void **)&var_getnext, payload_size,
+                               SMM_VARIABLE_FUNCTION_GET_NEXT_VARIABLE_NAME,
+                               &ret);
+       if (!comm_buf)
+               goto out;
+
+       /* Fill in contents */
+       guidcpy(&var_getnext->guid, guid);
+       var_getnext->name_size = out_name_size;
+       memcpy(var_getnext->name, variable_name, in_name_size);
+       memset((u8 *)var_getnext->name + in_name_size, 0x0,
+              out_name_size - in_name_size);
+
+       /* Communicate */
+       ret = mm_communicate(comm_buf, payload_size);
+       if (ret == EFI_SUCCESS || ret == EFI_BUFFER_TOO_SMALL) {
+               /* Update with reported data size for trimmed case */
+               *variable_name_size = var_getnext->name_size;
+       }
+       if (ret != EFI_SUCCESS)
+               goto out;
+
+       guidcpy(guid, &var_getnext->guid);
+       memcpy(variable_name, (u8 *)var_getnext->name,
+              var_getnext->name_size);
+
+out:
+       free(comm_buf);
+       return EFI_EXIT(ret);
+}
+
+/**
+ * efi_set_variable() - set value of a UEFI variable
+ *
+ * This function implements the SetVariable runtime service.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * @name:              name of the variable
+ * @guid:              vendor GUID
+ * @attr:              attributes of the variable
+ * @data_size:         size of the buffer with the variable value
+ * @data:              buffer with the variable value
+ * Return:             status code
+ */
+efi_status_t EFIAPI efi_set_variable(u16 *name, const efi_guid_t *guid,
+                                    u32 attr, efi_uintn_t data_size,
+                                    const void *data)
+{
+       struct smm_variable_access *var_acc;
+       efi_uintn_t payload_size;
+       efi_uintn_t name_size;
+       u8 *comm_buf = NULL;
+       efi_status_t ret;
+
+       EFI_ENTRY("\"%ls\" %pUl %x %zu %p", name, guid, attr, data_size, data);
+
+       if (!name || name[0] == 0 || !guid) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+       if (data_size > 0 && !data) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+
+       /* Check payload size */
+       name_size = u16_strsize(name);
+       payload_size = MM_VARIABLE_ACCESS_HEADER_SIZE + name_size + data_size;
+       if (payload_size > max_payload_size) {
+               ret = EFI_INVALID_PARAMETER;
+               goto out;
+       }
+
+       /* Get communication buffer and initialize header */
+       comm_buf = setup_mm_hdr((void **)&var_acc, payload_size,
+                               SMM_VARIABLE_FUNCTION_SET_VARIABLE, &ret);
+       if (!comm_buf)
+               goto out;
+
+       /* Fill in contents */
+       guidcpy(&var_acc->guid, guid);
+       var_acc->data_size = data_size;
+       var_acc->name_size = name_size;
+       var_acc->attr = attr;
+       memcpy(var_acc->name, name, name_size);
+       memcpy((u8 *)var_acc->name + name_size, data, data_size);
+
+       /* Communicate */
+       ret = mm_communicate(comm_buf, payload_size);
+
+out:
+       free(comm_buf);
+       return EFI_EXIT(ret);
+}
+
+/**
+ * efi_query_variable_info() - get information about EFI variables
+ *
+ * This function implements the QueryVariableInfo() runtime service.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * @attributes:                                bitmask to select variables to be
+ *                                     queried
+ * @maximum_variable_storage_size:     maximum size of storage area for the
+ *                                     selected variable types
+ * @remaining_variable_storage_size:   remaining size of storage are for the
+ *                                     selected variable types
+ * @maximum_variable_size:             maximum size of a variable of the
+ *                                     selected type
+ * Returns:                            status code
+ */
+efi_status_t EFIAPI __efi_runtime
+efi_query_variable_info(u32 attributes, u64 *max_variable_storage_size,
+                       u64 *remain_variable_storage_size,
+                       u64 *max_variable_size)
+{
+       struct smm_variable_query_info *mm_query_info;
+       efi_uintn_t payload_size;
+       efi_status_t ret;
+       u8 *comm_buf;
+
+       EFI_ENTRY("%x %p %p %p", attributes, max_variable_storage_size,
+                 remain_variable_storage_size, max_variable_size);
+
+       payload_size = sizeof(*mm_query_info);
+       comm_buf = setup_mm_hdr((void **)&mm_query_info, payload_size,
+                               SMM_VARIABLE_FUNCTION_QUERY_VARIABLE_INFO,
+                               &ret);
+       if (!comm_buf)
+               goto out;
+
+       mm_query_info->attr = attributes;
+       ret = mm_communicate(comm_buf, payload_size);
+       if (ret != EFI_SUCCESS)
+               goto out;
+       *max_variable_storage_size = mm_query_info->max_variable_storage;
+       *remain_variable_storage_size =
+                       mm_query_info->remaining_variable_storage;
+       *max_variable_size = mm_query_info->max_variable_size;
+
+out:
+       free(comm_buf);
+       return EFI_EXIT(ret);
+}
+
+/**
+ * efi_get_variable_runtime() - runtime implementation of GetVariable()
+ *
+ * @variable_name:     name of the variable
+ * @guid:              vendor GUID
+ * @attributes:                attributes of the variable
+ * @data_size:         size of the buffer to which the variable value is copied
+ * @data:              buffer to which the variable value is copied
+ * Return:             status code
+ */
+static efi_status_t __efi_runtime EFIAPI
+efi_get_variable_runtime(u16 *variable_name, const efi_guid_t *guid,
+                        u32 *attributes, efi_uintn_t *data_size, void *data)
+{
+       return EFI_UNSUPPORTED;
+}
+
+/**
+ * efi_get_next_variable_name_runtime() - runtime implementation of
+ *                                       GetNextVariable()
+ *
+ * @variable_name_size:        size of variable_name buffer in byte
+ * @variable_name:     name of uefi variable's name in u16
+ * @guid:              vendor's guid
+ * Return:              status code
+ */
+static efi_status_t __efi_runtime EFIAPI
+efi_get_next_variable_name_runtime(efi_uintn_t *variable_name_size,
+                                  u16 *variable_name, efi_guid_t *guid)
+{
+       return EFI_UNSUPPORTED;
+}
+
+/**
+ * efi_query_variable_info() - get information about EFI variables
+ *
+ * This function implements the QueryVariableInfo() runtime service.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * @attributes:                                bitmask to select variables to be
+ *                                     queried
+ * @maximum_variable_storage_size:     maximum size of storage area for the
+ *                                     selected variable types
+ * @remaining_variable_storage_size:   remaining size of storage are for the
+ *                                     selected variable types
+ * @maximum_variable_size:             maximum size of a variable of the
+ *                                     selected type
+ * Return:                             status code
+ */
+efi_status_t EFIAPI __efi_runtime
+efi_query_variable_info_runtime(u32 attributes, u64 *max_variable_storage_size,
+                               u64 *remain_variable_storage_size,
+                               u64 *max_variable_size)
+{
+       return EFI_UNSUPPORTED;
+}
+
+/**
+ * efi_set_variable_runtime() - runtime implementation of SetVariable()
+ *
+ * @variable_name:     name of the variable
+ * @guid:              vendor GUID
+ * @attributes:                attributes of the variable
+ * @data_size:         size of the buffer with the variable value
+ * @data:              buffer with the variable value
+ * Return:             status code
+ */
+static efi_status_t __efi_runtime EFIAPI
+efi_set_variable_runtime(u16 *variable_name, const efi_guid_t *guid,
+                        u32 attributes, efi_uintn_t data_size,
+                        const void *data)
+{
+       return EFI_UNSUPPORTED;
+}
+
+/**
+ * efi_variables_boot_exit_notify() - notify ExitBootServices() is called
+ */
+void efi_variables_boot_exit_notify(void)
+{
+       u8 *comm_buf;
+       efi_status_t ret;
+
+       comm_buf = setup_mm_hdr(NULL, 0,
+                               SMM_VARIABLE_FUNCTION_EXIT_BOOT_SERVICE, &ret);
+       if (comm_buf)
+               ret = mm_communicate(comm_buf, 0);
+       else
+               ret = EFI_NOT_FOUND;
+
+       if (ret != EFI_SUCCESS)
+               log_err("Unable to notify StMM for ExitBootServices\n");
+       free(comm_buf);
+
+       /* Update runtime service table */
+       efi_runtime_services.query_variable_info =
+                       efi_query_variable_info_runtime;
+       efi_runtime_services.get_variable = efi_get_variable_runtime;
+       efi_runtime_services.get_next_variable_name =
+                       efi_get_next_variable_name_runtime;
+       efi_runtime_services.set_variable = efi_set_variable_runtime;
+       efi_update_table_header_crc32(&efi_runtime_services.hdr);
+}
+
+/**
+ * efi_init_variables() - initialize variable services
+ *
+ * Return:     status code
+ */
+efi_status_t efi_init_variables(void)
+{
+       efi_status_t ret;
+
+       ret = get_max_payload(&max_payload_size);
+       if (ret != EFI_SUCCESS)
+               return ret;
+
+       max_buffer_size = MM_COMMUNICATE_HEADER_SIZE +
+                         MM_VARIABLE_COMMUNICATE_SIZE +
+                         max_payload_size;
+
+       return EFI_SUCCESS;
+}