crypto/internal/fips140: add Supported

Move the logic duplicated in multiple places to a central function.

Change-Id: I6a6a4656469c91dd62b0be716ec8367358f4a3e1
Reviewed-on: https://go-review.googlesource.com/c/go/+/639336
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
Reviewed-by: Roland Shoemaker <roland@golang.org>

src/cmd/dist/test.go

@@ -1797,6 +1797,8 @@ func isEnvSet(evar string) bool {
 }
 
 func (t *tester) fipsSupported() bool {
+	// Keep this in sync with [crypto/internal/fips140.Supported].
+
 	// Use GOFIPS140 or GOEXPERIMENT=boringcrypto, but not both.
 	if strings.Contains(goexperiment, "boringcrypto") {
 		return false

src/crypto/internal/fips140/asan.go

@@ -4,6 +4,6 @@
 
 //go:build asan
 
-package check
+package fips140
 
 const asanEnabled = true

src/crypto/internal/fips140/boring.go

@@ -0,0 +1,10 @@
+// Copyright 2024 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.
+
+// Keep in sync with notboring.go and crypto/internal/boring/boring.go.
+//go:build boringcrypto && linux && (amd64 || arm64) && !android && !msan && cgo
+
+package fips140
+
+const boringEnabled = true

src/crypto/internal/fips140/check/check.go

@@ -19,7 +19,6 @@ import (
 	"crypto/internal/fips140deps/byteorder"
 	"crypto/internal/fips140deps/godebug"
 	"io"
-	"runtime"
 	"unsafe"
 )
 
@@ -27,19 +26,6 @@ import (
 // true when [fips140.Enabled] is true, or init would have panicked.
 var Verified bool
 
-// Supported reports whether the current GOOS/GOARCH is Supported at all.
-func Supported() bool {
-	// See cmd/internal/obj/fips.go's EnableFIPS for commentary.
-	switch {
-	case runtime.GOARCH == "wasm",
-		runtime.GOOS == "windows" && runtime.GOARCH == "386",
-		runtime.GOOS == "windows" && runtime.GOARCH == "arm",
-		runtime.GOOS == "aix":
-		return false
-	}
-	return true
-}
-
 // Linkinfo holds the go:fipsinfo symbol prepared by the linker.
 // See cmd/link/internal/ld/fips.go for details.
 //
@@ -70,19 +56,8 @@ func init() {
 		return
 	}
 
-	if asanEnabled {
-		// ASAN disapproves of reading swaths of global memory below.
-		// One option would be to expose runtime.asanunpoison through
-		// crypto/internal/fips140deps and then call it to unpoison the range
-		// before reading it, but it is unclear whether that would then cause
-		// false negatives. For now, FIPS+ASAN doesn't need to work.
-		// If this is made to work, also re-enable the test in check_test.go
-		// and in cmd/dist/test.go.
-		panic("fips140: cannot verify in asan mode")
-	}
-
-	if !Supported() {
-		panic("fips140: unavailable on " + runtime.GOOS + "-" + runtime.GOARCH)
+	if err := fips140.Supported(); err != nil {
+		panic("fips140: " + err.Error())
 	}
 
 	if Linkinfo.Magic[0] != 0xff || string(Linkinfo.Magic[1:]) != fipsMagic || Linkinfo.Sum == zeroSum {

src/crypto/internal/fips140/fips140.go

@@ -4,7 +4,11 @@
 
 package fips140
 
-import "crypto/internal/fips140deps/godebug"
+import (
+	"crypto/internal/fips140deps/godebug"
+	"errors"
+	"runtime"
+)
 
 var Enabled bool
 
@@ -24,6 +28,35 @@ func init() {
 	}
 }
 
+// Supported returns an error if FIPS 140-3 mode can't be enabled.
+func Supported() error {
+	// Keep this in sync with fipsSupported in cmd/dist/test.go.
+
+	// ASAN disapproves of reading swaths of global memory in fips140/check.
+	// One option would be to expose runtime.asanunpoison through
+	// crypto/internal/fips140deps and then call it to unpoison the range
+	// before reading it, but it is unclear whether that would then cause
+	// false negatives. For now, FIPS+ASAN doesn't need to work.
+	if asanEnabled {
+		return errors.New("FIPS 140-3 mode is incompatible with ASAN")
+	}
+
+	// See EnableFIPS in cmd/internal/obj/fips.go for commentary.
+	switch {
+	case runtime.GOARCH == "wasm",
+		runtime.GOOS == "windows" && runtime.GOARCH == "386",
+		runtime.GOOS == "windows" && runtime.GOARCH == "arm",
+		runtime.GOOS == "aix":
+		return errors.New("FIPS 140-3 mode is not supported on " + runtime.GOOS + "-" + runtime.GOARCH)
+	}
+
+	if boringEnabled {
+		return errors.New("FIPS 140-3 mode is incompatible with GOEXPERIMENT=boringcrypto")
+	}
+
+	return nil
+}
+
 func Name() string {
 	return "Go Cryptographic Module"
 }

src/crypto/internal/fips140/notasan.go

@@ -4,6 +4,6 @@
 
 //go:build !asan
 
-package check
+package fips140
 
 const asanEnabled = false

src/crypto/internal/fips140/notboring.go

@@ -0,0 +1,9 @@
+// Copyright 2024 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.
+
+//go:build !(boringcrypto && linux && (amd64 || arm64) && !android && !msan && cgo)
+
+package fips140
+
+const boringEnabled = false

src/crypto/internal/fips140test/check_test.go

@@ -5,16 +5,14 @@
 package fipstest
 
 import (
-	"crypto/internal/boring"
+	"crypto/internal/fips140"
 	. "crypto/internal/fips140/check"
 	"crypto/internal/fips140/check/checktest"
 	"fmt"
 	"internal/abi"
-	"internal/asan"
 	"internal/godebug"
 	"internal/testenv"
 	"os"
-	"runtime"
 	"testing"
 	"unicode"
 	"unsafe"
@@ -23,10 +21,6 @@ import (
 const enableFIPSTest = true
 
 func TestFIPSCheckVerify(t *testing.T) {
-	if boring.Enabled {
-		t.Skip("not testing fips140 with boringcrypto enabled")
-	}
-
 	if Verified {
 		t.Logf("verified")
 		return
@@ -40,12 +34,8 @@ func TestFIPSCheckVerify(t *testing.T) {
 		return
 	}
 
-	if !Supported() {
-		t.Skipf("skipping on %s-%s", runtime.GOOS, runtime.GOARCH)
-	}
-	if asan.Enabled {
-		// Verification panics with asan; don't bother.
-		t.Skipf("skipping with -asan")
+	if err := fips140.Supported(); err != nil {
+		t.Skipf("skipping: %v", err)
 	}
 
 	cmd := testenv.Command(t, os.Args[0], "-test.v", "-test.run=TestFIPSCheck")
@@ -62,8 +52,8 @@ func TestFIPSCheckInfo(t *testing.T) {
 		return
 	}
 
-	if !Supported() {
-		t.Skipf("skipping on %s-%s", runtime.GOOS, runtime.GOARCH)
+	if err := fips140.Supported(); err != nil {
+		t.Skipf("skipping: %v", err)
 	}
 
 	// Check that the checktest symbols are initialized properly.