diff --git a/sys/sys/asan.h b/sys/sys/asan.h
--- a/sys/sys/asan.h
+++ b/sys/sys/asan.h
@@ -65,4 +65,6 @@
 #define kasan_mark(p, s, l, c)
 #endif /* !KASAN */
 
+#define	kasan_poison_pointer(x)	kasan_mark(&x, 0, sizeof(x), KASAN_GENERIC_REDZONE)
+
 #endif /* !_SYS_ASAN_H_ */
diff --git a/sys/sys/buf.h b/sys/sys/buf.h
--- a/sys/sys/buf.h
+++ b/sys/sys/buf.h
@@ -522,8 +522,7 @@
 extern int	dirtybufferflushes;
 extern int	altbufferflushes;
 extern int	nswbuf;			/* Number of swap I/O buffer headers. */
-extern caddr_t __read_mostly unmapped_buf; /* Data address for unmapped
-					      buffers. */
+extern caddr_t	unmapped_buf;		/* Data address for unmapped buffers. */
 
 static inline int
 buf_mapped(struct buf *bp)
diff --git a/sys/sys/kassert.h b/sys/sys/kassert.h
--- a/sys/sys/kassert.h
+++ b/sys/sys/kassert.h
@@ -38,6 +38,39 @@
 extern bool panicked;
 #define	KERNEL_PANICKED()	__predict_false(panicked)
 
+/*
+ * Trap accesses going through a pointer. Moreover if kasan is available trap
+ * reading the pointer itself.
+ *
+ * Sample usage: you have a struct with numerous fields and by API contract
+ * only some of them get populated, even if the implementation temporary writes
+ * to them. You can DEBUG_POISON_POINTER so the consumer which should no be
+ * looking at the field gets caught.
+ *
+ * DEBUG_POISON_POINTER(obj->ptr);
+ * ....
+ * if (obj->ptr != NULL) // traps with kasan, does not trap otherwise
+ * ....
+ * obj->ptr->field // traps with and without kasan
+ */
+#ifdef	INVARIANTS
+
+#include <sys/asan.h>
+
+#ifndef	DEBUG_POISON_POINTER_VALUE
+extern caddr_t unmapped_buf;
+#define	DEBUG_POISON_POINTER_VALUE unmapped_buf
+#endif
+
+#define DEBUG_POISON_POINTER(x) ({				\
+	x = (void *)(DEBUG_POISON_POINTER_VALUE);		\
+	kasan_poison_pointer(x);				\
+})
+
+#else
+#define DEBUG_POISON_POINTER(x)
+#endif
+
 #ifdef	INVARIANTS		/* The option is always available */
 #define	VNASSERT(exp, vp, msg) do {					\
 	if (__predict_false(!(exp))) {					\