Switch ProcessPrng back to RtlGenRandom (revert 693def1)

src/crypto/rand/rand.go

@@ -16,7 +16,7 @@ import "io"
 //   - On macOS and iOS, Reader uses arc4random_buf(3).
 //   - On OpenBSD and NetBSD, Reader uses getentropy(2).
 //   - On other Unix-like systems, Reader reads from /dev/urandom.
-//   - On Windows, Reader uses the ProcessPrng API.
+//   - On Windows, Reader uses the RtlGenRandom API.
 //   - On js/wasm, Reader uses the Web Crypto API.
 //   - On wasip1/wasm, Reader uses random_get from wasi_snapshot_preview1.
 var Reader io.Reader

src/crypto/rand/rand_windows.go

@@ -15,8 +15,11 @@ func init() { Reader = &rngReader{} }
 
 type rngReader struct{}
 
-func (r *rngReader) Read(b []byte) (int, error) {
+func (r *rngReader) Read(b []byte) (n int, err error) {
-	if err := windows.ProcessPrng(b); err != nil {
+	// RtlGenRandom only returns 1<<32-1 bytes at a time. We only read at
+	// most 1<<31-1 bytes at a time so that  this works the same on 32-bit
+	// and 64-bit systems.
+	if err := batched(windows.RtlGenRandom, 1<<31-1)(b); err != nil {
 		return 0, err
 	}
 	return len(b), nil

src/internal/syscall/windows/syscall_windows.go

@@ -414,7 +414,7 @@ func ErrorLoadingGetTempPath2() error {
 //sys	DestroyEnvironmentBlock(block *uint16) (err error) = userenv.DestroyEnvironmentBlock
 //sys	CreateEvent(eventAttrs *SecurityAttributes, manualReset uint32, initialState uint32, name *uint16) (handle syscall.Handle, err error) = kernel32.CreateEventW
 
-//sys	ProcessPrng(buf []byte) (err error) = bcryptprimitives.ProcessPrng
+//sys	RtlGenRandom(buf []byte) (err error) = advapi32.SystemFunction036
 
 type FILE_ID_BOTH_DIR_INFO struct {
 	NextEntryOffset uint32

src/internal/syscall/windows/zsyscall_windows.go

@@ -38,7 +38,6 @@ func errnoErr(e syscall.Errno) error {
 
 var (
 	modadvapi32         = syscall.NewLazyDLL(sysdll.Add("advapi32.dll"))
-	modbcryptprimitives = syscall.NewLazyDLL(sysdll.Add("bcryptprimitives.dll"))
 	modiphlpapi         = syscall.NewLazyDLL(sysdll.Add("iphlpapi.dll"))
 	modkernel32         = syscall.NewLazyDLL(sysdll.Add("kernel32.dll"))
 	modnetapi32         = syscall.NewLazyDLL(sysdll.Add("netapi32.dll"))
@@ -57,7 +56,7 @@ var (
 	procQueryServiceStatus                = modadvapi32.NewProc("QueryServiceStatus")
 	procRevertToSelf                      = modadvapi32.NewProc("RevertToSelf")
 	procSetTokenInformation               = modadvapi32.NewProc("SetTokenInformation")
-	procProcessPrng                       = modbcryptprimitives.NewProc("ProcessPrng")
+	procSystemFunction036                 = modadvapi32.NewProc("SystemFunction036")
 	procGetAdaptersAddresses              = modiphlpapi.NewProc("GetAdaptersAddresses")
 	procCreateEventW                      = modkernel32.NewProc("CreateEventW")
 	procGetACP                            = modkernel32.NewProc("GetACP")
@@ -183,12 +182,12 @@ func SetTokenInformation(tokenHandle syscall.Token, tokenInformationClass uint32
 	return
 }
 
-func ProcessPrng(buf []byte) (err error) {
+func RtlGenRandom(buf []byte) (err error) {
 	var _p0 *byte
 	if len(buf) > 0 {
 		_p0 = &buf[0]
 	}
-	r1, _, e1 := syscall.Syscall(procProcessPrng.Addr(), 2, uintptr(unsafe.Pointer(_p0)), uintptr(len(buf)), 0)
+	r1, _, e1 := syscall.Syscall(procSystemFunction036.Addr(), 2, uintptr(unsafe.Pointer(_p0)), uintptr(len(buf)), 0)
 	if r1 == 0 {
 		err = errnoErr(e1)
 	}

src/runtime/os_windows.go

@@ -127,8 +127,15 @@ var (
 	_WriteFile,
 	_ stdFunction
 
-	// Use ProcessPrng to generate cryptographically random data.
+	// Use RtlGenRandom to generate cryptographically random data.
-	_ProcessPrng stdFunction
+	// This approach has been recommended by Microsoft (see issue
+	// 15589 for details).
+	// The RtlGenRandom is not listed in advapi32.dll, instead
+	// RtlGenRandom function can be found by searching for SystemFunction036.
+	// Also some versions of Mingw cannot link to SystemFunction036
+	// when building executable as Cgo. So load SystemFunction036
+	// manually during runtime startup.
+	_RtlGenRandom stdFunction
 
 	// Load ntdll.dll manually during startup, otherwise Mingw
 	// links wrong printf function to cgo executable (see issue
@@ -146,10 +153,11 @@ var (
 )
 
 var (
-	bcryptprimitivesdll = [...]uint16{'b', 'c', 'r', 'y', 'p', 't', 'p', 'r', 'i', 'm', 'i', 't', 'i', 'v', 'e', 's', '.', 'd', 'l', 'l', 0}
+	advapi32dll = [...]uint16{'a', 'd', 'v', 'a', 'p', 'i', '3', '2', '.', 'd', 'l', 'l', 0}
-	ntdlldll            = [...]uint16{'n', 't', 'd', 'l', 'l', '.', 'd', 'l', 'l', 0}
+	ntdlldll    = [...]uint16{'n', 't', 'd', 'l', 'l', '.', 'd', 'l', 'l', 0}
-	powrprofdll         = [...]uint16{'p', 'o', 'w', 'r', 'p', 'r', 'o', 'f', '.', 'd', 'l', 'l', 0}
+	powrprofdll = [...]uint16{'p', 'o', 'w', 'r', 'p', 'r', 'o', 'f', '.', 'd', 'l', 'l', 0}
-	winmmdll            = [...]uint16{'w', 'i', 'n', 'm', 'm', '.', 'd', 'l', 'l', 0}
+	winmmdll    = [...]uint16{'w', 'i', 'n', 'm', 'm', '.', 'd', 'l', 'l', 0}
+	ws2_32dll   = [...]uint16{'w', 's', '2', '_', '3', '2', '.', 'd', 'l', 'l', 0}
 )
 
 // Function to be called by windows CreateThread
@@ -263,11 +271,11 @@ func windows_QueryPerformanceFrequency() int64 {
 }
 
 func loadOptionalSyscalls() {
-	bcryptPrimitives := windowsLoadSystemLib(bcryptprimitivesdll[:])
+	a32 := windowsLoadSystemLib(advapi32dll[:])
-	if bcryptPrimitives == 0 {
+	if a32 == 0 {
-		throw("bcryptprimitives.dll not found")
+		throw("advapi32.dll not found")
 	}
-	_ProcessPrng = windowsFindfunc(bcryptPrimitives, []byte("ProcessPrng\000"))
+	_RtlGenRandom = windowsFindfunc(a32, []byte("SystemFunction036\000"))
 
 	n32 := windowsLoadSystemLib(ntdlldll[:])
 	if n32 == 0 {
@@ -500,7 +508,7 @@ func osinit() {
 //go:nosplit
 func readRandom(r []byte) int {
 	n := 0
-	if stdcall2(_ProcessPrng, uintptr(unsafe.Pointer(&r[0])), uintptr(len(r)))&0xff != 0 {
+	if stdcall2(_RtlGenRandom, uintptr(unsafe.Pointer(&r[0])), uintptr(len(r)))&0xff != 0 {
 		n = len(r)
 	}
 	return n