Check table version before calling UEFI 2.0+ functions

The create_event_ex function (in boot services) and query_variable_info
(in runtime services) were added to their respective tables in UEFI
2.0. In earlier versions these functions can't be called, so check the
table revision before using these function pointers.

Author: nicholasbishop

src/table/boot.rs

@@ -1,6 +1,6 @@
 //! UEFI services available during boot.
 
-use super::Header;
+use super::{Header, Revision};
 use crate::data_types::Align;
 use crate::proto::device_path::{DevicePath, FfiDevicePath};
 #[cfg(feature = "exts")]
@@ -437,6 +437,9 @@ impl BootServices {
     /// More than one event of type `EventType::TIMER` may be part of a single event group. However,
     /// there is no mechanism for determining which of the timers was signaled.
     ///
+    /// This operation is only supported starting with UEFI 2.0; earlier
+    /// versions will fail with [`Status::UNSUPPORTED`].
+    ///
     /// # Safety
     ///
     /// The caller must ensure they are passing a valid `Guid` as `event_group`, if applicable.
@@ -448,6 +451,10 @@ impl BootServices {
         notify_ctx: Option<NonNull<c_void>>,
         event_group: Option<NonNull<Guid>>,
     ) -> Result<Event> {
+        if self.header.revision < Revision::EFI_2_00 {
+            return Err(Status::UNSUPPORTED.into());
+        }
+
         let mut event = MaybeUninit::<Event>::uninit();
 
         (self.create_event_ex)(

src/table/runtime.rs

@@ -1,6 +1,6 @@
 //! UEFI services available at runtime, even after the OS boots.
 
-use super::Header;
+use super::{Header, Revision};
 #[cfg(feature = "exts")]
 use crate::data_types::FromSliceWithNulError;
 use crate::result::Error;
@@ -248,11 +248,18 @@ impl RuntimeServices {
     /// Get information about UEFI variable storage space for the type
     /// of variable specified in `attributes`.
     ///
+    /// This operation is only supported starting with UEFI 2.0; earlier
+    /// versions will fail with [`Status::UNSUPPORTED`].
+    ///
     /// See [`VariableStorageInfo`] for details of the information returned.
     pub fn query_variable_info(
         &self,
         attributes: VariableAttributes,
     ) -> Result<VariableStorageInfo> {
+        if self.header.revision < Revision::EFI_2_00 {
+            return Err(Status::UNSUPPORTED.into());
+        }
+
         let mut info = VariableStorageInfo::default();
         unsafe {
             (self.query_variable_info)(