Add heap with guard pages to detect out of bound reads/writes.

This is a very simple heap implementation that allocates memory so that
the end of each allocation always coincides with a page end and is
followed by a guard page which is marked non-present. Out of bounds
access (both read and write) therefore cause a crash (unhandled page
fault).

Note that this allocator is neither speed nor space efficient, indeed it
wastes huge amounts of pages and address space so it is quite easy to
hit limits. It is intended as a pure debug feature.

build/config_headers/kernel_debug_config.h

@@ -101,12 +101,28 @@
 // Enables swap support.
 #define ENABLE_SWAP_SUPPORT				1
 
-// Use the slab allocator as generic memory allocator (malloc()/free()).
+// Use the selected allocator as generic memory allocator (malloc()/free()).
+#define USE_DEBUG_HEAP_FOR_MALLOC		0
+	// Heap implementation with additional debugging facilities.
+#define USE_GUARDED_HEAP_FOR_MALLOC		0
+	// Heap implementation that allocates memory so that the end of the
+	// allocation always coincides with a page end and is followed by a guard
+	// page which is marked non-present. Out of bounds access (both read and
+	// write) therefore cause a crash (unhandled page fault). Note that this
+	// allocator is neither speed nor space efficient, indeed it wastes huge
+	// amounts of pages and address space so it is quite easy to hit limits.
 #define USE_SLAB_ALLOCATOR_FOR_MALLOC	1
+	// Heap implementation based on the slab allocator (for production use).
 
 // Enables additional sanity checks in the slab allocator's memory manager.
 #define DEBUG_SLAB_MEMORY_MANAGER_PARANOID_CHECKS	0
 
+// Disables memory re-use in the guarded heap (freed memory is never reused and
+// stays invalid causing every access to crash). Note that this is a magnitude
+// more space inefficient than the guarded heap itself. Fully booting may not
+// work at all due to address space waste.
+#define DEBUG_GUARDED_HEAP_DISABLE_MEMORY_REUSE		0
+
 // When set limits the amount of available RAM (in MB).
 //#define LIMIT_AVAILABLE_MEMORY		256
 

build/config_headers/tracing_config.h

@@ -28,6 +28,8 @@
 #define BMESSAGE_TRACING						0
 #define FILE_DESCRIPTOR_TRACING					0
 #define FILE_DESCRIPTOR_TRACING_STACK_TRACE		0	/* stack trace depth */
+#define GUARDED_HEAP_TRACING					0
+#define GUARDED_HEAP_TRACING_STACK_TRACE		0	/* stack trace depth */
 #define IO_CONTEXT_TRACING						0
 #define IO_CONTEXT_TRACING_STACK_TRACE			0	/* stack trace depth */
 #define KERNEL_HEAP_TRACING						0