fix: add support for darwin/arm64 (#7)

This diff ensures we hardcode the capabilities of darwin/arm64.

While there, strive to make the packages naming slightly less confusing.

Reference issue: ooni/probe#2122.

Surpersedes (and draws from) #5.

Co-authored-by: ain ghazal ainghazal42@gmail.com

Co-authored-by: ain ghazal <ainghazal42@gmail.com>

aes/cipher_asm.go

@@ -9,7 +9,7 @@ package aes
 import (
 	"crypto/cipher"
 
-	"github.com/ooni/oocrypto/internal/cpuarm64"
+	"github.com/ooni/oocrypto/internal/cpuoverlay"
 	"github.com/ooni/oocrypto/internal/subtle"
 	"golang.org/x/sys/cpu"
 )
@@ -29,8 +29,8 @@ type aesCipherAsm struct {
 	aesCipher
 }
 
-var supportsAES = cpu.X86.HasAES || cpuarm64.HasAES()
-var supportsGFMUL = cpu.X86.HasPCLMULQDQ || cpuarm64.HasPMULL()
+var supportsAES = cpu.X86.HasAES || cpuoverlay.Arm64HasAES()
+var supportsGFMUL = cpu.X86.HasPCLMULQDQ || cpuoverlay.Arm64HasPMULL()
 
 // aesCipherGCM implements crypto/cipher.gcmAble so that crypto/cipher.NewGCM
 // will use the optimised implementation in aes_gcm.go when possible.

internal/cpuoverlay/cpoverlay_otherwise.go

@@ -0,0 +1,22 @@
+//go:build !arm64 || (!darwin && !android)
+
+package cpuoverlay
+
+import "golang.org/x/sys/cpu"
+
+//
+// This file is built when we're not on arm64 or we're on windows/arm64. In the
+// former case, just returning false would do. In the latter case, the right thing
+// to do is to return cpu.ARM64.HasXXX. Because cpu.ARM64.HasXXX are always false
+// when not on arm64, we conflate these two cases in a single file.
+//
+
+// arm64HasAES returns whether the CPU supports AES.
+func arm64HasAES() bool {
+	return cpu.ARM64.HasAES
+}
+
+// arm64HasPMULL returns whether the CPU supports PMULL.
+func arm64HasPMULL() bool {
+	return cpu.ARM64.HasPMULL
+}

internal/cpuoverlay/cpuoverlay.go

@@ -0,0 +1,44 @@
+// Package cpuoverlay is a logic overlay on top of x/sys/cpu that
+// attempts to avoid cases in which x/sys/cpu is wrong.
+//
+// android/arm64
+//
+// The main problem that we want to solve is that on Android there are
+// cases where reading /proc/self/auxv is not possible.
+//
+// This causes crypto/tls to not choose AES where it would otherwise
+// be possible, in turn causing censorship. See also the
+// https://github.com/ooni/probe/issues/1444 issue for more details.
+//
+// Ideally we would like to call getauxval(3) when initializing
+// the runtime package. However, runtime cannot use CGO. Doing that
+// leads to an import loop, so we cannot build.
+//
+// Until this is fixed in src/runtime, we call getauxval(3) here.
+//
+// darwin/arm64
+//
+// Additionally, we may use this package to solve other CPU issues. For
+// example, x/sys/cpu does not currently know about darwin/arm64 features.
+//
+// Design
+//
+// This package contains GOOS/GOARCH-specific files with predicate
+// functions returning the correct value in cases in which x/sys/cpu
+// is wrong. You are expected to replace the code that normally
+// lives inside src/crypto/tls and src/cryto/aes and that we have
+// forked in this repository such that you call the predicates
+// of this package as opposed to using directly x/sys/cpu values.
+package cpuoverlay
+
+// We dispatch to GOOS/GOARCH specific implementations
+
+// Arm64HasAES returns whether the CPU supports AES.
+func Arm64HasAES() bool {
+	return arm64HasAES()
+}
+
+// Arm64HasPMULL returns whether the CPU supports PMULL.
+func Arm64HasPMULL() bool {
+	return arm64HasPMULL()
+}

internal/cpuarm64/cpuarm64_android_arm64.go → internal/cpuoverlay/cpuoverlay_android_arm64.go

@@ -1,4 +1,4 @@
-//go:build android && arm64
+//go:build arm64 && android
 
 // Copyright 2019 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -7,7 +7,13 @@
 // This file is based on the diff available at
 // https://go-review.googlesource.com/c/sys/+/197540/
 
-package cpuarm64
+package cpuoverlay
+
+//
+// On android/arm64 /proc/sys/auxv is not readable on most
+// systems, therefore we need to call getauxval to load the
+// correct values, otherwise we think there's no HW AES.
+//
 
 /*
 #include <sys/auxv.h>
@@ -67,12 +73,12 @@ const (
 	hwcap_CPUID   = 1 << 11
 )
 
-// HasAES returns whether the CPU supports AES.
-func HasAES() bool {
+// arm64HasAES returns whether the CPU supports AES.
+func arm64HasAES() bool {
 	return (gethwcap() & hwcap_AES) != 0
 }
 
-// HasPMULL returns whether the CPU supports PMULL.
-func HasPMULL() bool {
+// arm64HasPMULL returns whether the CPU supports PMULL.
+func arm64HasPMULL() bool {
 	return (gethwcap() & hwcap_PMULL) != 0
 }

internal/cpuoverlay/cpuoverlay_darwin_arm64.go

@@ -0,0 +1,24 @@
+//go:build arm64 && darwin
+
+package cpuoverlay
+
+//
+// As documented below, there's no support for detecting the
+// capabilities of darwin/arm64 in x/sys/cpu so we're going to
+// do what internal/cpu currently is doing, i.e., hardcoding
+// true because we know M1 supports these HW capabilities.
+//
+// See https://github.com/ooni/probe/issues/2122
+//
+// See https://github.com/golang/go/issues/43046
+//
+
+// arm64HasAES returns whether the CPU supports AES.
+func arm64HasAES() bool {
+	return true
+}
+
+// arm64HasPMULL returns whether the CPU supports PMULL.
+func arm64HasPMULL() bool {
+	return true
+}

tls/cipher_suites.go

@@ -18,7 +18,7 @@ import (
 
 	"github.com/ooni/oocrypto/aes"
 	"github.com/ooni/oocrypto/internal/boring"
-	"github.com/ooni/oocrypto/internal/cpuarm64"
+	"github.com/ooni/oocrypto/internal/cpuoverlay"
 	"golang.org/x/crypto/chacha20poly1305"
 	"golang.org/x/sys/cpu"
 )
@@ -357,7 +357,7 @@ var defaultCipherSuitesTLS13NoAES = []uint16{
 
 var (
 	hasGCMAsmAMD64 = cpu.X86.HasAES && cpu.X86.HasPCLMULQDQ
-	hasGCMAsmARM64 = cpuarm64.HasAES() && cpuarm64.HasPMULL()
+	hasGCMAsmARM64 = cpuoverlay.Arm64HasAES() && cpuoverlay.Arm64HasPMULL()
 	// Keep in sync with crypto/aes/cipher_s390x.go.
 	hasGCMAsmS390X = cpu.S390X.HasAES && cpu.S390X.HasAESCBC && cpu.S390X.HasAESCTR &&
 		(cpu.S390X.HasGHASH || cpu.S390X.HasAESGCM)