Rework memguard(9) to reserve significantly more KVA to detect

use-after-free over a longer time.  Also release the backing pages of
a guarded allocation at free(9) time to reduce the overhead of using
memguard(9).  Allow setting and varying the malloc type at run-time.
Add knobs to allow:

 - randomly guarding memory
 - adding un-backed KVA guard pages to detect underflow and overflow
 - a lower limit on the size of allocations that are guarded

Reviewed by:    alc
Reviewed by:    brueffer, Ulrich Spörlein <uqs spoerlein net> (man page)
Silence from:   -arch
Approved by:    zml (mentor)
MFC after:      1 month

1 files changed, 16 insertions, 5 deletions

diff --git a/sys/vm/memguard.h b/sys/vm/memguard.h
index cabcc0a..55ffec9 100644
--- a/sys/vm/memguard.h
+++ b/sys/vm/memguard.h
@@ -26,9 +26,20 @@
  * $FreeBSD$
  */
 
-extern u_int vm_memguard_divisor;
+#include "opt_vm.h"
 
-void	memguard_init(vm_map_t parent_map, unsigned long size);
-void 	*memguard_alloc(unsigned long size, int flags);
-void	memguard_free(void *addr);
-int	memguard_cmp(struct malloc_type *mtp);
+#ifdef DEBUG_MEMGUARD
+unsigned long	memguard_fudge(unsigned long, unsigned long);
+void	memguard_init(struct vm_map *);
+void 	*memguard_alloc(unsigned long, int);
+void	memguard_free(void *);
+int	memguard_cmp(struct malloc_type *, unsigned long);
+int	is_memguard_addr(void *);
+#else
+#define	memguard_fudge(size, xxx)	(size)
+#define	memguard_init(map)		do { } while (0)
+#define	memguard_alloc(size, flags)	NULL
+#define	memguard_free(addr)		do { } while (0)
+#define	memguard_cmp(mtp, size)		0
+#define	is_memguard_addr(addr)		0
+#endif