misc/cgo/testsanitizers: add libfuzzer tests

Apparently we don't have tests for libfuzzer mode. Add some tests.

Updates #57449.

Change-Id: I813da3e71c6d6f15db31914b248db220b0b7041e
Reviewed-on: https://go-review.googlesource.com/c/go/+/459555
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>

misc/cgo/testsanitizers/cc_test.go

@@ -353,6 +353,9 @@ func configure(sanitizer string) *config {
 		// Set the debug mode to print the C stack trace.
 		c.cFlags = append(c.cFlags, "-g")
 
+	case "fuzzer":
+		c.goFlags = append(c.goFlags, "-tags=libfuzzer", "-gcflags=-d=libfuzzer")
+
 	default:
 		panic(fmt.Sprintf("unrecognized sanitizer: %q", sanitizer))
 	}
@@ -405,6 +408,13 @@ int main() {
 }
 `)
 
+var cLibFuzzerInput = []byte(`
+#include <stddef.h>
+int LLVMFuzzerTestOneInput(char *data, size_t size) {
+	return 0;
+}
+`)
+
 func (c *config) checkCSanitizer() (skip bool, err error) {
 	dir, err := os.MkdirTemp("", c.sanitizer)
 	if err != nil {
@@ -413,7 +423,12 @@ func (c *config) checkCSanitizer() (skip bool, err error) {
 	defer os.RemoveAll(dir)
 
 	src := filepath.Join(dir, "return0.c")
-	if err := os.WriteFile(src, cMain, 0600); err != nil {
+	cInput := cMain
+	if c.sanitizer == "fuzzer" {
+		// libFuzzer generates the main function itself, and uses a different input.
+		cInput = cLibFuzzerInput
+	}
+	if err := os.WriteFile(src, cInput, 0600); err != nil {
 		return false, fmt.Errorf("failed to write C source file: %v", err)
 	}
 
@@ -434,6 +449,11 @@ func (c *config) checkCSanitizer() (skip bool, err error) {
 		return true, fmt.Errorf("%#q failed: %v\n%s", strings.Join(cmd.Args, " "), err, out)
 	}
 
+	if c.sanitizer == "fuzzer" {
+		// For fuzzer, don't try running the test binary. It never finishes.
+		return false, nil
+	}
+
 	if out, err := exec.Command(dst).CombinedOutput(); err != nil {
 		if os.IsNotExist(err) {
 			return true, fmt.Errorf("%#q failed to produce executable: %v", strings.Join(cmd.Args, " "), err)
@@ -505,6 +525,10 @@ func (d *tempDir) RemoveAll(t *testing.T) {
 	}
 }
 
+func (d *tempDir) Base() string {
+	return d.base
+}
+
 func (d *tempDir) Join(name string) string {
 	return filepath.Join(d.base, name)
 }
@@ -535,7 +559,7 @@ func hangProneCmd(name string, arg ...string) *exec.Cmd {
 }
 
 // mSanSupported is a copy of the function cmd/internal/sys.MSanSupported,
-// because the internal pacakage can't be used here.
+// because the internal package can't be used here.
 func mSanSupported(goos, goarch string) bool {
 	switch goos {
 	case "linux":
@@ -548,7 +572,7 @@ func mSanSupported(goos, goarch string) bool {
 }
 
 // aSanSupported is a copy of the function cmd/internal/sys.ASanSupported,
-// because the internal pacakage can't be used here.
+// because the internal package can't be used here.
 func aSanSupported(goos, goarch string) bool {
 	switch goos {
 	case "linux":

misc/cgo/testsanitizers/libfuzzer_test.go

@@ -0,0 +1,90 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sanitizers_test
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestLibFuzzer(t *testing.T) {
+	goos, err := goEnv("GOOS")
+	if err != nil {
+		t.Fatal(err)
+	}
+	goarch, err := goEnv("GOARCH")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !libFuzzerSupported(goos, goarch) {
+		t.Skipf("skipping on %s/%s; libfuzzer option is not supported.", goos, goarch)
+	}
+	config := configure("fuzzer")
+	config.skipIfCSanitizerBroken(t)
+
+	cases := []struct {
+		goSrc         string
+		cSrc          string
+		expectedError string
+	}{
+		{goSrc: "libfuzzer1.go", expectedError: "panic: found it"},
+		{goSrc: "libfuzzer2.go", cSrc: "libfuzzer2.c", expectedError: "panic: found it"},
+	}
+	for _, tc := range cases {
+		tc := tc
+		name := strings.TrimSuffix(tc.goSrc, ".go")
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			dir := newTempDir(t)
+			defer dir.RemoveAll(t)
+
+			// build Go code in libfuzzer mode to a c-archive
+			outPath := dir.Join(name)
+			archivePath := dir.Join(name + ".a")
+			mustRun(t, config.goCmd("build", "-buildmode=c-archive", "-o", archivePath, srcPath(tc.goSrc)))
+
+			// build C code (if any) and link with Go code
+			cmd, err := cc(config.cFlags...)
+			if err != nil {
+				t.Fatalf("error running cc: %v", err)
+			}
+			cmd.Args = append(cmd.Args, config.ldFlags...)
+			cmd.Args = append(cmd.Args, "-o", outPath, "-I", dir.Base())
+			if tc.cSrc != "" {
+				cmd.Args = append(cmd.Args, srcPath(tc.cSrc))
+			}
+			cmd.Args = append(cmd.Args, archivePath)
+			mustRun(t, cmd)
+
+			cmd = hangProneCmd(outPath)
+			outb, err := cmd.CombinedOutput()
+			out := string(outb)
+			if err == nil {
+				t.Fatalf("fuzzing succeeded unexpectedly; output:\n%s", out)
+			}
+			if !strings.Contains(out, tc.expectedError) {
+				t.Errorf("exited without expected error %q; got\n%s", tc.expectedError, out)
+			}
+		})
+	}
+}
+
+// libFuzzerSupported is a copy of the function internal/platform.FuzzInstrumented,
+// because the internal package can't be used here.
+func libFuzzerSupported(goos, goarch string) bool {
+	switch goarch {
+	case "amd64", "arm64":
+		// TODO(#14565): support more architectures.
+		switch goos {
+		case "darwin", "freebsd", "linux", "windows":
+			return true
+		default:
+			return false
+		}
+	default:
+		return false
+	}
+}

misc/cgo/testsanitizers/testdata/libfuzzer1.go

@@ -0,0 +1,16 @@
+package main
+
+import "C"
+
+import "unsafe"
+
+//export LLVMFuzzerTestOneInput
+func LLVMFuzzerTestOneInput(p unsafe.Pointer, sz C.int) C.int {
+	b := C.GoBytes(p, sz)
+	if len(b) >= 6 && b[0] == 'F' && b[1] == 'u' && b[2] == 'z' && b[3] == 'z' && b[4] == 'M' && b[5] == 'e' {
+		panic("found it")
+	}
+	return 0
+}
+
+func main() {}

misc/cgo/testsanitizers/testdata/libfuzzer2.c

@@ -0,0 +1,11 @@
+#include <stddef.h>
+
+#include "libfuzzer2.h"
+
+int LLVMFuzzerTestOneInput(char *data, size_t size) {
+ 	if (size > 0 && data[0] == 'H')
+		if (size > 1 && data[1] == 'I')
+			if (size > 2 && data[2] == '!')
+				FuzzMe(data, size);
+	return 0;
+}

misc/cgo/testsanitizers/testdata/libfuzzer2.go

@@ -0,0 +1,16 @@
+package main
+
+import "C"
+
+import "unsafe"
+
+//export FuzzMe
+func FuzzMe(p unsafe.Pointer, sz C.int) {
+	b := C.GoBytes(p, sz)
+	b = b[3:]
+	if len(b) >= 4 && b[0] == 'f' && b[1] == 'u' && b[2] == 'z' && b[3] == 'z' {
+		panic("found it")
+	}
+}
+
+func main() {}