Cygwin: threads: use mmap area to fulfill requests for big stacks

Otherwise big stacks have a higher probability to collide with
randomized PEBs and TEBs after fork.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

1 files changed, 6 insertions, 4 deletions

diff --git a/winsup/cygwin/miscfuncs.cc b/winsup/cygwin/miscfuncs.cc
index 1ed9684f1..e1eb5e8e2 100644
--- a/winsup/cygwin/miscfuncs.cc
+++ b/winsup/cygwin/miscfuncs.cc
@@ -515,11 +515,13 @@ public:
     BOOL overflow = FALSE;
     PVOID real_stackaddr = NULL;
 
-    /* If an application requests a monster stack, we fulfill this request
-       from outside of our pool, top down. */
+    /* If an application requests a monster stack, fulfill request
+       from mmap area. */
     if (real_size > THREAD_STACK_MAX)
-      return VirtualAlloc (NULL, real_size, MEM_RESERVE | MEM_TOP_DOWN,
-			   PAGE_READWRITE);
+      {
+	PVOID addr = mmap_alloc.alloc (NULL, real_size, false);
+	return VirtualAlloc (addr, real_size, MEM_RESERVE, PAGE_READWRITE);
+      }
     /* Simple round-robin.  Keep looping until VirtualAlloc succeeded, or
        until we overflowed and hit the current address. */
     for (UINT_PTR addr = current - real_size;