SELFOUR-220: only delete reply cap when waiting on sync endpoint

haskell/src/SEL4/API/Syscall.lhs

@@ -178,13 +178,14 @@ The "Wait" system call blocks waiting to receive a message through a specified e
 > handleWait :: Kernel ()
 > handleWait = do
 >     thread <- getCurThread
->     deleteCallerCap thread
 >     epCPtr <- asUser thread $ liftM CPtr $ getRegister capRegister
 >     (capFaultOnFailure epCPtr True $ do
 >         epCap <- lookupCap thread epCPtr
 >         case epCap of
 >             EndpointCap { capEPCanReceive = True } ->
->                 withoutFailure $ receiveIPC thread epCap
+>                 withoutFailure $ do 
+>                     deleteCallerCap thread
+>                     receiveIPC thread epCap
 >             AsyncEndpointCap { capAEPCanReceive = True } ->
 >                 withoutFailure $ receiveAsyncIPC thread epCap
 >             _ -> throw $ MissingCapability { missingCapBitsLeft = 0 })

src/api/syscall.c

@@ -308,8 +308,6 @@ handleWait(void)
     word_t epCPtr;
     lookupCap_ret_t lu_ret;
 
-    deleteCallerCap(ksCurThread);
-
     epCPtr = getRegister(ksCurThread, capRegister);
 
     lu_ret = lookupCap(ksCurThread, epCPtr);
@@ -322,6 +320,7 @@ handleWait(void)
 
     switch (cap_get_capType(lu_ret.cap)) {
     case cap_endpoint_cap:
+
         if (unlikely(!cap_endpoint_cap_get_capCanReceive(lu_ret.cap))) {
             current_lookup_fault = lookup_fault_missing_capability_new(0);
             current_fault = fault_cap_fault_new(epCPtr, true);
@@ -329,6 +328,7 @@ handleWait(void)
             break;
         }
 
+        deleteCallerCap(ksCurThread);
         receiveIPC(ksCurThread, lu_ret.cap);
         break;