Free unused trampoline regions on abort and attach error

Similar to the implementation in SlimDetoursTransactionCommit.

Author: m417z

Source/SlimDetours/SlimDetours.inl

@@ -266,6 +266,10 @@ detour_free_trampoline(
 
 VOID detour_free_unused_trampoline_regions(VOID);
 
+VOID
+detour_free_trampoline_region_if_unused(
+    _In_ PDETOUR_TRAMPOLINE pTrampoline);
+
 BYTE
 detour_align_from_trampoline(
     _In_ PDETOUR_TRAMPOLINE pTrampoline,

Source/SlimDetours/Trampoline.c

@@ -400,24 +400,29 @@ detour_is_region_empty(
     return TRUE;
 }
 
+static
 VOID
-detour_free_unused_trampoline_regions(VOID)
+detour_free_region(
+    _In_ PDETOUR_REGION* ppRegionBase,
+    _In_ PDETOUR_REGION pRegion)
 {
-    PVOID pMem;
-    SIZE_T sMem;
+    *ppRegionBase = pRegion->pNext;
+    PVOID pMem = pRegion;
+    SIZE_T sMem = 0;
+    NtFreeVirtualMemory(NtCurrentProcess(), &pMem, &sMem, MEM_RELEASE);
+}
 
+VOID
+detour_free_unused_trampoline_regions(VOID)
+{
     PDETOUR_REGION* ppRegionBase = &s_pRegions;
     PDETOUR_REGION pRegion = s_pRegions;
 
     while (pRegion != NULL)
     {
         if (detour_is_region_empty(pRegion))
         {
-            *ppRegionBase = pRegion->pNext;
-
-            pMem = pRegion;
-            sMem = 0;
-            NtFreeVirtualMemory(NtCurrentProcess(), &pMem, &sMem, MEM_RELEASE);
+            detour_free_region(ppRegionBase, pRegion);
             s_pRegion = NULL;
         } else
         {
@@ -427,6 +432,32 @@ detour_free_unused_trampoline_regions(VOID)
     }
 }
 
+VOID
+detour_free_trampoline_region_if_unused(
+    _In_ PDETOUR_TRAMPOLINE pTrampoline)
+{
+    PDETOUR_REGION pTargetRegion = (PDETOUR_REGION)((ULONG_PTR)pTrampoline & ~(ULONG_PTR)0xffff);
+
+    PDETOUR_REGION* ppRegionBase = &s_pRegions;
+    PDETOUR_REGION pRegion = s_pRegions;
+
+    while (pRegion != NULL)
+    {
+        if (pRegion == pTargetRegion)
+        {
+            if (detour_is_region_empty(pRegion))
+            {
+                detour_free_region(ppRegionBase, pRegion);
+                s_pRegion = NULL;
+            }
+            break;
+        }
+
+        ppRegionBase = &pRegion->pNext;
+        pRegion = *ppRegionBase;
+    }
+}
+
 BYTE
 detour_align_from_trampoline(
     _In_ PDETOUR_TRAMPOLINE pTrampoline,

Source/SlimDetours/Transaction.c

@@ -98,6 +98,7 @@ SlimDetoursTransactionAbort(VOID)
     PVOID pMem;
     SIZE_T sMem;
     DWORD dwOld;
+    BOOL freed = FALSE;
 
     if (s_nPendingThreadId != NtCurrentThreadId())
     {
@@ -115,13 +116,18 @@ SlimDetoursTransactionAbort(VOID)
         {
             detour_free_trampoline(o->pTrampoline);
             o->pTrampoline = NULL;
+            freed = TRUE;
         }
 
         PDETOUR_OPERATION n = o->pNext;
         detour_memory_free(o);
         o = n;
     }
     s_pPendingOperations = NULL;
+    if (freed)
+    {
+        detour_free_unused_trampoline_regions();
+    }
 
     // Make sure the trampoline pages are no longer writable.
     detour_runnable_trampoline_regions();
@@ -324,6 +330,7 @@ SlimDetoursAttach(
         if (pTrampoline != NULL)
         {
             detour_free_trampoline(pTrampoline);
+            detour_free_trampoline_region_if_unused(pTrampoline);
             pTrampoline = NULL;
         }
         if (o != NULL)