# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1709421161 -3600
# Node ID e96c7cbee506769de204b23a97b72a70c6940b68
# Parent  5d590f2cc5894ad00980ce053817dbde7053d16d
Introduced barrier pages between the UTCB region and each of the stacks.

diff -r 5d590f2cc589 -r e96c7cbee506 libexec/lib/src/process_creating.cc
--- a/libexec/lib/src/process_creating.cc	Sat Mar 02 23:51:22 2024 +0100
+++ b/libexec/lib/src/process_creating.cc	Sun Mar 03 00:12:41 2024 +0100
@@ -59,7 +59,11 @@
   if (err)
     return err;
 
-  _rm_stack = new ExplicitSegment(Utcb_area_start - initial_stack_size, initial_stack_size, L4_FPAGE_RW);
+  /* Introduce a page as a barrier between the UTCB and the stack. */
+
+  _rm_stack = new ExplicitSegment(Utcb_area_start - L4_PAGESIZE -
+    initial_stack_size, initial_stack_size, L4_FPAGE_RW);
+
   return _rm_stack->allocate(true);
 }
 
@@ -74,7 +78,12 @@
   if (err)
     return err;
 
-  _program_stack = new ExplicitSegment(Utcb_area_start - initial_stack_size * 2, initial_stack_size, L4_FPAGE_RW);
+  /* Introduce a page as a barrier between the program stack and the region
+     mapper stack. */
+
+  _program_stack = new ExplicitSegment(Utcb_area_start - L4_PAGESIZE * 2 -
+    initial_stack_size * 2, initial_stack_size, L4_FPAGE_RW);
+
   return _program_stack->allocate(true);
 }