From e4e59921f1cc11e60f0096bcb4d54dd683270821 Mon Sep 17 00:00:00 2001
From: Austin Clements <austin@google.com>
Date: Mon, 24 Aug 2015 13:35:49 -0400
Subject: [PATCH] [release-branch.go1.5] cmd/compile: fix uninitialized memory
 in compare of interface value

A comparison of the form l == r where l is an interface and r is
concrete performs a type assertion on l to convert it to r's type.
However, the compiler fails to zero the temporary where the result of
the type assertion is written, so if the type is a pointer type and a
stack scan occurs while in the type assertion, it may see an invalid
pointer on the stack.

Fix this by zeroing the temporary. This is equivalent to the fix for
type switches from c4092ac.

Fixes #12253.

Change-Id: Iaf205d456b856c056b317b4e888ce892f0c555b9
Reviewed-on: https://go-review.googlesource.com/13872
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-on: https://go-review.googlesource.com/14242
Reviewed-by: Austin Clements <austin@google.com>
---
 src/cmd/compile/internal/gc/walk.go |  5 +++++
 src/runtime/export_test.go          |  1 +
 src/runtime/gc_test.go              | 17 +++++++++++++++++
 src/runtime/iface.go                |  5 +++++
 4 files changed, 28 insertions(+)

diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index ce73018b8b..af3e1ccbe4 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -3219,6 +3219,11 @@ func walkcompare(np **Node, init **NodeList) {
 
 	if l != nil {
 		x := temp(r.Type)
+		if haspointers(r.Type) {
+			a := Nod(OAS, x, nil)
+			typecheck(&a, Etop)
+			*init = list(*init, a)
+		}
 		ok := temp(Types[TBOOL])
 
 		// l.(type(r))
diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go
index 16d54765b7..f14dc30a7f 100644
--- a/src/runtime/export_test.go
+++ b/src/runtime/export_test.go
@@ -154,3 +154,4 @@ func BenchSetType(n int, x interface{}) {
 const PtrSize = ptrSize
 
 var TestingAssertE2I2GC = &testingAssertE2I2GC
+var TestingAssertE2T2GC = &testingAssertE2T2GC
diff --git a/src/runtime/gc_test.go b/src/runtime/gc_test.go
index 636e5248c8..6c9b314c65 100644
--- a/src/runtime/gc_test.go
+++ b/src/runtime/gc_test.go
@@ -469,3 +469,20 @@ func testAssertVar(x interface{}) error {
 	}
 	return nil
 }
+
+func TestAssertE2T2Liveness(t *testing.T) {
+	*runtime.TestingAssertE2T2GC = true
+	defer func() {
+		*runtime.TestingAssertE2T2GC = false
+	}()
+
+	poisonStack()
+	testIfaceEqual(io.EOF)
+}
+
+func testIfaceEqual(x interface{}) {
+	if x == "abc" {
+		// Prevent inlining
+		panic("")
+	}
+}
diff --git a/src/runtime/iface.go b/src/runtime/iface.go
index abd7068ed1..332b7d50ab 100644
--- a/src/runtime/iface.go
+++ b/src/runtime/iface.go
@@ -229,8 +229,13 @@ func assertE2T(t *_type, e interface{}, r unsafe.Pointer) {
 	}
 }
 
+var testingAssertE2T2GC bool
+
 // The compiler ensures that r is non-nil.
 func assertE2T2(t *_type, e interface{}, r unsafe.Pointer) bool {
+	if testingAssertE2T2GC {
+		GC()
+	}
 	ep := (*eface)(unsafe.Pointer(&e))
 	if ep._type != t {
 		memclr(r, uintptr(t.size))
-- 
2.48.1