kata-os-camkes: wrap request ipc buffer capability handling

Add Camkes::set_request_cap to attach an seL4 capability to an outbound
ipc message. The return value is an RAII wrapper that cleans up state
and must be held until after the CAmkES rpc call completes

Change-Id: I0672c59e0b5e43e39c9ea3fb16809270a33f51ef
GitOrigin-RevId: 56be13a2c05fcc1b4a1aa5c8e0eab47bcd0f2345

apps/system/components/kata-os-common/src/camkes/src/lib.rs

@@ -12,6 +12,7 @@ use sel4_sys;
 use sel4_sys::seL4_CNode_Delete;
 use sel4_sys::seL4_CPtr;
 use sel4_sys::seL4_GetCapReceivePath;
+use sel4_sys::seL4_SetCap;
 use sel4_sys::seL4_SetCapReceivePath;
 use sel4_sys::seL4_Word;
 use sel4_sys::seL4_WordBits;
@@ -28,6 +29,14 @@ extern "C" {
     static SELF_CNODE_LAST_SLOT: seL4_CPtr;
 }
 
+// RAII wrapper for handling request cap cleanup.
+pub struct RequestCapCleanup {}
+impl Drop for RequestCapCleanup {
+    fn drop(&mut self) {
+        unsafe { seL4_SetCap(0, 0); }
+    }
+}
+
 pub struct Camkes {
     name: &'static str, // Component name
     recv_path: seL4_CPath, // IPCBuffer receive path
@@ -115,6 +124,14 @@ impl Camkes {
                 self.get_current_recv_path(), self.recv_path);
     }
 
+    // Attaches a capability to a CAmkES RPC request msg. seL4 will copy
+    // the capabiltiy.
+    #[must_use]
+    pub fn set_request_cap(cptr: seL4_CPtr) -> RequestCapCleanup {
+        unsafe { seL4_SetCap(0, cptr); }
+        RequestCapCleanup{}
+    }
+
     // Wrappers for sel4_sys::debug_assert macros.
     pub fn debug_assert_slot_empty(tag: &str, path: &seL4_CPath) {
         sel4_sys::debug_assert_slot_empty!(path.1,