cmd/link: for asan align coverage counter section to 8 bytes

Fixes #66966

Change-Id: I92777a7d7d8afaa82ffcd605aa3e607289b645f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/622477
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/cgo/internal/testsanitizers/asan_test.go

@@ -7,6 +7,7 @@
 package sanitizers_test
 
 import (
+	"bytes"
 	"fmt"
 	"internal/platform"
 	"internal/testenv"
@@ -15,34 +16,9 @@ import (
 )
 
 func TestASAN(t *testing.T) {
-	testenv.MustHaveGoBuild(t)
-	testenv.MustHaveCGO(t)
-	goos, err := goEnv("GOOS")
-	if err != nil {
-		t.Fatal(err)
-	}
-	goarch, err := goEnv("GOARCH")
-	if err != nil {
-		t.Fatal(err)
-	}
-	// The asan tests require support for the -asan option.
-	if !platform.ASanSupported(goos, goarch) {
-		t.Skipf("skipping on %s/%s; -asan option is not supported.", goos, goarch)
-	}
-	// The current implementation is only compatible with the ASan library from version
-	// v7 to v9 (See the description in src/runtime/asan/asan.go). Therefore, using the
-	// -asan option must use a compatible version of ASan library, which requires that
-	// the gcc version is not less than 7 and the clang version is not less than 9,
-	// otherwise a segmentation fault will occur.
-	if !compilerRequiredAsanVersion(goos, goarch) {
-		t.Skipf("skipping on %s/%s: too old version of compiler", goos, goarch)
-	}
+	config := mustHaveASAN(t)
 
 	t.Parallel()
-	requireOvercommit(t)
-	config := configure("address")
-	config.skipIfCSanitizerBroken(t)
-
 	mustRun(t, config.goCmd("build", "std"))
 
 	cases := []struct {
@@ -106,29 +82,10 @@ func TestASAN(t *testing.T) {
 }
 
 func TestASANLinkerX(t *testing.T) {
-	testenv.MustHaveGoBuild(t)
-	testenv.MustHaveCGO(t)
 	// Test ASAN with linker's -X flag (see issue 56175).
-	goos, err := goEnv("GOOS")
-	if err != nil {
-		t.Fatal(err)
-	}
-	goarch, err := goEnv("GOARCH")
-	if err != nil {
-		t.Fatal(err)
-	}
-	// The asan tests require support for the -asan option.
-	if !platform.ASanSupported(goos, goarch) {
-		t.Skipf("skipping on %s/%s; -asan option is not supported.", goos, goarch)
-	}
-	if !compilerRequiredAsanVersion(goos, goarch) {
-		t.Skipf("skipping on %s/%s: too old version of compiler", goos, goarch)
-	}
+	config := mustHaveASAN(t)
 
 	t.Parallel()
-	requireOvercommit(t)
-	config := configure("address")
-	config.skipIfCSanitizerBroken(t)
 
 	dir := newTempDir(t)
 	defer dir.RemoveAll(t)
@@ -147,3 +104,56 @@ func TestASANLinkerX(t *testing.T) {
 	// run the binary
 	mustRun(t, hangProneCmd(outPath))
 }
+
+// Issue 66966.
+func TestASANFuzz(t *testing.T) {
+	config := mustHaveASAN(t)
+
+	t.Parallel()
+
+	dir := newTempDir(t)
+	defer dir.RemoveAll(t)
+
+	cmd := config.goCmd("test", "-fuzz=Fuzz", srcPath("asan_fuzz_test.go"))
+	t.Logf("%v", cmd)
+	out, err := cmd.CombinedOutput()
+	t.Logf("%s", out)
+	if err == nil {
+		t.Error("expected fuzzing failure")
+	}
+	if bytes.Contains(out, []byte("AddressSanitizer")) {
+		t.Error(`output contains "AddressSanitizer", but should not`)
+	}
+}
+
+func mustHaveASAN(t *testing.T) *config {
+	testenv.MustHaveGoBuild(t)
+	testenv.MustHaveCGO(t)
+	goos, err := goEnv("GOOS")
+	if err != nil {
+		t.Fatal(err)
+	}
+	goarch, err := goEnv("GOARCH")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !platform.ASanSupported(goos, goarch) {
+		t.Skipf("skipping on %s/%s; -asan option is not supported.", goos, goarch)
+	}
+
+	// The current implementation is only compatible with the ASan library from version
+	// v7 to v9 (See the description in src/runtime/asan/asan.go). Therefore, using the
+	// -asan option must use a compatible version of ASan library, which requires that
+	// the gcc version is not less than 7 and the clang version is not less than 9,
+	// otherwise a segmentation fault will occur.
+	if !compilerRequiredAsanVersion(goos, goarch) {
+		t.Skipf("skipping on %s/%s: too old version of compiler", goos, goarch)
+	}
+
+	requireOvercommit(t)
+
+	config := configure("address")
+	config.skipIfCSanitizerBroken(t)
+
+	return config
+}

src/cmd/cgo/internal/testsanitizers/testdata/asan_fuzz_test.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"slices"
+	"testing"
+)
+
+func Reverse(s string) string {
+	runes := []rune(s)
+	slices.Reverse(runes)
+	return string(runes)
+}
+
+// This fuzz test should quickly fail, because Reverse doesn't
+// work for strings that are not valid UTF-8.
+// What we are testing for is whether we see a failure from ASAN;
+// we should see a fuzzing failure, not an ASAN failure.
+
+func FuzzReverse(f *testing.F) {
+	f.Add("Go")
+	f.Add("Gopher")
+	f.Add("Hello, 世界")
+	f.Fuzz(func(t *testing.T, s string) {
+		r1 := Reverse(s)
+		r2 := Reverse(r1)
+		if s != r2 {
+			t.Errorf("got %q want %q", r2, s)
+		}
+	})
+}

src/cmd/link/internal/ld/data.go

@@ -2981,6 +2981,12 @@ func (ctxt *Link) address() []*sym.Segment {
 	ctxt.xdefine("runtime.end", sym.SBSS, int64(Segdata.Vaddr+Segdata.Length))
 
 	if fuzzCounters != nil {
+		if *flagAsan {
+			// ASAN requires that the symbol marking the end
+			// of the section be aligned on an 8 byte boundary.
+			// See issue #66966.
+			fuzzCounters.Length = uint64(Rnd(int64(fuzzCounters.Length), 8))
+		}
 		ctxt.xdefine("runtime.__start___sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr))
 		ctxt.xdefine("runtime.__stop___sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr+fuzzCounters.Length))
 		ctxt.xdefine("internal/fuzz._counters", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr))