From e4e59921f1cc11e60f0096bcb4d54dd683270821 Mon Sep 17 00:00:00 2001
From: Austin Clements <[email protected]>
Date: Mon, 24 Aug 2015 13:35:49 -0400
Subject: [PATCH 09/63] [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 <[email protected]>
Reviewed-on: https://go-review.googlesource.com/14242
Reviewed-by: Austin Clements <[email protected]>
---
 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 ce73018..af3e1cc 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 16d5476..f14dc30 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 636e524..6c9b314 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 abd7068..332b7d5 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))
-- 
2.6.1