[PATCH v1 51/54] efi: loader: CONFIG_EFI_RT_VOLATILE_STORE

[Ahmad Fatoum]

If we store EFI variables on ESP during boottime, we need cooperation
from the OS to write that file to implement SetVariable.

Populate the necessary options to allow efivar(1) to read a dump
of the variables after writing them and then persist them to ESP.

Note that this violates the EFI spec and it's not power-fail safe, but
it's an ok fallback for now.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 efi/loader/Kconfig        | 18 ++++++++++++++
 efi/loader/efi_var_file.c | 51 +++++++++++++++++++++++++++++++++++++++
 efi/loader/runtime.c      |  4 +++
 efi/loader/variable.h     |  2 ++
 4 files changed, 75 insertions(+)

diff --git a/efi/loader/Kconfig b/efi/loader/Kconfig
index 4a5e4c375fd4..5692e54ebe01 100644
--- a/efi/loader/Kconfig
+++ b/efi/loader/Kconfig
@@ -68,6 +68,24 @@ config EFI_VARIABLE_NO_STORE
 
 endchoice
 
+config EFI_RT_VOLATILE_STORE
+	bool "Allow variable runtime services in volatile storage (e.g RAM)"
+	depends on EFI_VARIABLE_FILE_STORE
+	select EFI_RUNTIME_SET_VARIABLE
+	default y
+	help
+	  When EFI variables are stored on file we don't allow SetVariableRT,
+	  since the OS doesn't know how to write that file. At the same time
+	  we copy runtime variables in DRAM and support GetVariableRT
+
+	  Enable this option to allow SetVariableRT on the RAM backend of
+	  the EFI variable storage. The OS will be responsible for syncing
+	  the RAM contents to the file, otherwise any changes made during
+	  runtime won't persist reboots.
+	  Authenticated variables are not supported. Note that this will
+	  violate the EFI spec since writing auth variables will return
+	  EFI_INVALID_PARAMETER
+
 endmenu
 
 source "efi/loader/protocols/Kconfig"
diff --git a/efi/loader/efi_var_file.c b/efi/loader/efi_var_file.c
index 08a5c172cced..652354693ae7 100644
--- a/efi/loader/efi_var_file.c
+++ b/efi/loader/efi_var_file.c
@@ -184,6 +184,57 @@ efi_status_t efi_var_from_file(int dirfd, const char *filename)
 	free(buf);
 	return ret;
 }
+
+// SPDX-SnippetBegin
+// SPDX-Snippet-Comment: Origin-URL: https://github.com/u-boot/u-boot/blob/e9c34fab18a9a0022b36729afd8e262e062764e2/lib/efi_loader/efi_runtime.c
+
+efi_status_t efi_init_runtime_variable_supported(void)
+{
+	u8 s = 0;
+	int ret;
+
+	if (!IS_ENABLED(CONFIG_EFI_RT_VOLATILE_STORE))
+		return EFI_SUCCESS;
+
+	ret = efi_set_variable_int(u"RTStorageVolatile",
+				   &efi_file_store_vars_guid,
+				   EFI_VARIABLE_BOOTSERVICE_ACCESS |
+				   EFI_VARIABLE_RUNTIME_ACCESS |
+				   EFI_VARIABLE_READ_ONLY,
+				   strlen(efi_var_file_name) + 1,
+				   efi_var_file_name, false);
+	if (ret != EFI_SUCCESS) {
+		pr_err("Failed to set RTStorageVolatile\n");
+		return ret;
+	}
+	/*
+	 * This variable needs to be visible so users can read it,
+	 * but the real contents are going to be filled during
+	 * GetVariable
+	 */
+	ret = efi_set_variable_int(u"VarToFile",
+				   &efi_file_store_vars_guid,
+				   EFI_VARIABLE_BOOTSERVICE_ACCESS |
+				   EFI_VARIABLE_RUNTIME_ACCESS |
+				   EFI_VARIABLE_READ_ONLY,
+				   sizeof(s),
+				   &s, false);
+	if (ret != EFI_SUCCESS) {
+		pr_err("Failed to set VarToFile\n");
+		efi_set_variable_int(u"RTStorageVolatile",
+				     &efi_file_store_vars_guid,
+				     EFI_VARIABLE_BOOTSERVICE_ACCESS |
+				     EFI_VARIABLE_RUNTIME_ACCESS |
+				     EFI_VARIABLE_READ_ONLY,
+				     0, NULL, false);
+		return ret;
+	}
+
+	return EFI_SUCCESS;
+}
+
+// SPDX-SnippetEnd
+
 static int efi_init_var_params(void)
 {
 	if (efi_is_payload())
diff --git a/efi/loader/runtime.c b/efi/loader/runtime.c
index b46c85eeaa7b..4b3cb6df1350 100644
--- a/efi/loader/runtime.c
+++ b/efi/loader/runtime.c
@@ -71,6 +71,10 @@ efi_status_t efi_init_runtime_supported(void)
 		CHECK_RT_FLAG(QUERY_CAPSULE_CAPABILITIES) |
 		CHECK_RT_FLAG(QUERY_VARIABLE_INFO);
 
+	ret = efi_init_runtime_variable_supported();
+	if (ret != EFI_SUCCESS)
+		return ret;
+
 	return efi_install_configuration_table(&efi_rt_properties_table_guid, rt_table);
 }
 
diff --git a/efi/loader/variable.h b/efi/loader/variable.h
index 3710be84a2d1..775bd11dc450 100644
--- a/efi/loader/variable.h
+++ b/efi/loader/variable.h
@@ -2,6 +2,8 @@
 #include <efi/types.h>
 #include <efi/error.h>
 
+efi_status_t efi_init_runtime_variable_supported(void);
+
 efi_status_t EFIAPI efi_get_variable_boot(u16 *variable_name,
 					  const efi_guid_t *vendor, u32 *attributes,
 					  efi_uintn_t *data_size, void *data);
-- 
2.47.3