efi_loader: fix append write behavior to non-existent variable

Current "variables" efi_selftest result is inconsistent
between the U-Boot file storage and the tee-based StandaloneMM
RPMB secure storage.

U-Boot file storage implementation does not accept SetVariale
call to non-existent variable with EFI_VARIABLE_APPEND_WRITE,
it return EFI_NOT_FOUND.
However it is accepted and new variable is created in EDK II
StandaloneMM implementation if valid data and size are specified.
If data size is 0, EFI_SUCCESS is returned.

Since UEFI specification does not clearly describe the behavior
of the append write to non-existent variable, let's update
the U-Boot file storage implementation to get aligned with
the EDK II reference implementation.

Signed-off-by: Masahisa Kojima <kojima.masahisa@socionext.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/lib/efi_selftest/efi_selftest_variables.c b/lib/efi_selftest/efi_selftest_variables.c
index c7a3fdb..39ad03a0 100644
--- a/lib/efi_selftest/efi_selftest_variables.c
+++ b/lib/efi_selftest/efi_selftest_variables.c
@@ -131,13 +131,57 @@
 			    (unsigned int)len);
 	if (memcmp(data, v, len))
 		efi_st_todo("GetVariable returned wrong value\n");
-	/* Append variable 2 */
+
+	/* Append variable 2, write to non-existent variable with datasize=0 */
 	ret = runtime->set_variable(u"efi_none", &guid_vendor1,
 				    EFI_VARIABLE_BOOTSERVICE_ACCESS |
 				    EFI_VARIABLE_APPEND_WRITE,
+				    0, v);
+	if (ret != EFI_SUCCESS) {
+		efi_st_error(
+			"SetVariable(APPEND_WRITE) with size 0 to non-existent variable returns wrong code\n");
+		return EFI_ST_FAILURE;
+	}
+	len = EFI_ST_MAX_DATA_SIZE;
+	ret = runtime->get_variable(u"efi_none", &guid_vendor1,
+				    &attr, &len, data);
+	if (ret != EFI_NOT_FOUND) {
+		efi_st_error("Variable must not be created\n");
+		return EFI_ST_FAILURE;
+	}
+	/* Append variable 2, write to non-existent variable with valid data size*/
+	ret = runtime->set_variable(u"efi_none", &guid_vendor1,
+				    EFI_VARIABLE_BOOTSERVICE_ACCESS |
+				    EFI_VARIABLE_APPEND_WRITE,
 				    15, v);
+	if (ret != EFI_SUCCESS) {
+		efi_st_error("SetVariable(APPEND_WRITE) with valid size and data to non-existent variable must be succcessful\n");
+		return EFI_ST_FAILURE;
+	}
+	len = EFI_ST_MAX_DATA_SIZE;
+	ret = runtime->get_variable(u"efi_none", &guid_vendor1,
+				    &attr, &len, data);
+	if (ret != EFI_SUCCESS) {
+		efi_st_error("GetVariable failed\n");
+		return EFI_ST_FAILURE;
+	}
+	if (len != 15)
+		efi_st_todo("GetVariable returned wrong length %u\n",
+			    (unsigned int)len);
+	if (memcmp(data, v, len))
+		efi_st_todo("GetVariable returned wrong value\n");
+	/* Delete variable efi_none */
+	ret = runtime->set_variable(u"efi_none", &guid_vendor1,
+				    0, 0, NULL);
+	if (ret != EFI_SUCCESS) {
+		efi_st_error("SetVariable failed\n");
+		return EFI_ST_FAILURE;
+	}
+	len = EFI_ST_MAX_DATA_SIZE;
+	ret = runtime->get_variable(u"efi_none", &guid_vendor1,
+				    &attr, &len, data);
 	if (ret != EFI_NOT_FOUND) {
-		efi_st_error("SetVariable(APPEND_WRITE) with size 0 to non-existent variable returns wrong code\n");
+		efi_st_error("Variable was not deleted\n");
 		return EFI_ST_FAILURE;
 	}
 	/* Enumerate variables */