[release-branch.go1.20] crypto/rand,runtime: revert "switch RtlGenRandom for ProcessPrng"

This reverts CL 545356.

Reason for revert: 1.20 still supports Windows versions before
ProcessPrng was introduced.

Change-Id: I224b8c4e7d0ca9ad5e733819b24dd92d14e61ab8
Reviewed-on: https://go-review.googlesource.com/c/go/+/545995
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>

Author: rolandshoemaker

src/crypto/rand/rand.go

@@ -15,7 +15,7 @@ import "io"
 // available, /dev/urandom otherwise.
 // On OpenBSD and macOS, Reader uses getentropy(2).
 // On other Unix-like systems, Reader reads from /dev/urandom.
-// On Windows systems, Reader uses the ProcessPrng API.
+// On Windows systems, Reader uses the RtlGenRandom API.
 // On Wasm, Reader uses the Web Crypto API.
 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) {
-	if err := windows.ProcessPrng(b); err != nil {
+func (r *rngReader) Read(b []byte) (n int, err error) {
+	// 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

@@ -366,4 +366,4 @@ func LoadGetFinalPathNameByHandle() error {
 //sys	CreateEnvironmentBlock(block **uint16, token syscall.Token, inheritExisting bool) (err error) = userenv.CreateEnvironmentBlock
 //sys	DestroyEnvironmentBlock(block *uint16) (err error) = userenv.DestroyEnvironmentBlock
 
-//sys	ProcessPrng(buf []byte) (err error) = bcryptprimitives.ProcessPrng
+//sys	RtlGenRandom(buf []byte) (err error) = advapi32.SystemFunction036

src/internal/syscall/windows/zsyscall_windows.go

@@ -122,8 +122,15 @@ var (
 	_LoadLibraryExW,
 	_ stdFunction
 
-	// Use ProcessPrng to generate cryptographically random data.
-	_ProcessPrng stdFunction
+	// Use RtlGenRandom to generate cryptographically random data.
+	// 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
@@ -249,12 +256,12 @@ func loadOptionalSyscalls() {
 	_LoadLibraryExW = windowsFindfunc(k32, []byte("LoadLibraryExW\000"))
 	useLoadLibraryEx = (_LoadLibraryExW != nil && _LoadLibraryExA != nil && _AddDllDirectory != nil)
 
-	var bcryptprimitivesdll = []byte("bcryptprimitives.dll\000")
-	bcryptPrimitives := windowsLoadSystemLib(bcryptprimitivesdll)
-	if bcryptPrimitives == 0 {
-		throw("bcryptprimitives.dll not found")
+	var advapi32dll = []byte("advapi32.dll\000")
+	a32 := windowsLoadSystemLib(advapi32dll)
+	if a32 == 0 {
+		throw("advapi32.dll not found")
 	}
-	_ProcessPrng = windowsFindfunc(bcryptPrimitives, []byte("ProcessPrng\000"))
+	_RtlGenRandom = windowsFindfunc(a32, []byte("SystemFunction036\000"))
 
 	var ntdll = []byte("ntdll.dll\000")
 	n32 := windowsLoadSystemLib(ntdll)
@@ -637,7 +644,7 @@ func initWine(k32 uintptr) {
 //go:nosplit
 func getRandomData(r []byte) {
 	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)
 	}
 	extendRandom(r, n)