runtime: validate lfnode addresses

Change-Id: Ic8c506289caaf6218494e5150d10002e0232feaa
Reviewed-on: https://go-review.googlesource.com/85876
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

src/runtime/lfstack.go

@@ -55,3 +55,13 @@ func (head *lfstack) pop() unsafe.Pointer {
 func (head *lfstack) empty() bool {
 	return atomic.Load64((*uint64)(head)) == 0
 }
+
+// lfnodeValidate panics if node is not a valid address for use with
+// lfstack.push. This only needs to be called when node is allocated.
+func lfnodeValidate(node *lfnode) {
+	if lfstackUnpack(lfstackPack(node, ^uintptr(0))) != node {
+		printlock()
+		println("runtime: bad lfnode address", hex(uintptr(unsafe.Pointer(node))))
+		throw("bad lfnode address")
+	}
+}

src/runtime/mgcwork.go

@@ -400,6 +400,7 @@ func getempty() *workbuf {
 		for i := uintptr(0); i+_WorkbufSize <= workbufAlloc; i += _WorkbufSize {
 			newb := (*workbuf)(unsafe.Pointer(s.base() + i))
 			newb.nobj = 0
+			lfnodeValidate(&newb.node)
 			if i == 0 {
 				b = newb
 			} else {