Auto merge of #45370 - alexcrichton:update-windows-rand, r=sfackler

std: Update randomness implementation on Windows

This commit updates the OS random number generator on Windows to match the
upstream implementation in the `rand` crate. First proposed in
rust-random/rand#111 this implementation uses a "private" API of
`RtlGenRandom`. Despite the [documentation][dox] indicating this is a private
function its widespread use in Chromium and Firefox as well as [comments] from
Microsoft internally indicates that it's highly unlikely to break.

Another motivation for switching this is to also attempt to make progress
on #44911. It may be the case that this function succeeds while the previous
implementation may fail in "weird" scenarios.

[dox]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa387694(v=vs.85).aspx
[comments]: rust-random/rand#111 (comment)

src/libstd/sys/windows/c.rs

@@ -37,7 +37,6 @@ pub type BOOL = c_int;
 pub type BYTE = u8;
 pub type BOOLEAN = BYTE;
 pub type GROUP = c_uint;
-pub type LONG_PTR = isize;
 pub type LARGE_INTEGER = c_longlong;
 pub type LONG = c_long;
 pub type UINT = c_uint;
@@ -46,7 +45,6 @@ pub type USHORT = c_ushort;
 pub type SIZE_T = usize;
 pub type WORD = u16;
 pub type CHAR = c_char;
-pub type HCRYPTPROV = LONG_PTR;
 pub type ULONG_PTR = usize;
 pub type ULONG = c_ulong;
 #[cfg(target_arch = "x86_64")]
@@ -288,10 +286,6 @@ pub const IMAGE_FILE_MACHINE_I386: DWORD = 0x014c;
 #[cfg(feature = "backtrace")]
 pub const IMAGE_FILE_MACHINE_AMD64: DWORD = 0x8664;
 
-pub const PROV_RSA_FULL: DWORD = 1;
-pub const CRYPT_SILENT: DWORD = 64;
-pub const CRYPT_VERIFYCONTEXT: DWORD = 0xF0000000;
-
 pub const EXCEPTION_CONTINUE_SEARCH: LONG = 0;
 pub const EXCEPTION_STACK_OVERFLOW: DWORD = 0xc00000fd;
 pub const EXCEPTION_MAXIMUM_PARAMETERS: usize = 15;
@@ -1136,15 +1130,6 @@ extern "system" {
  pub fn GetProcAddress(handle: HMODULE,
  name: LPCSTR) -> *mut c_void;
  pub fn GetModuleHandleW(lpModuleName: LPCWSTR) -> HMODULE;
- pub fn CryptAcquireContextA(phProv: *mut HCRYPTPROV,
- pszContainer: LPCSTR,
- pszProvider: LPCSTR,
- dwProvType: DWORD,
- dwFlags: DWORD) -> BOOL;
- pub fn CryptGenRandom(hProv: HCRYPTPROV,
- dwLen: DWORD,
- pbBuffer: *mut BYTE) -> BOOL;
- pub fn CryptReleaseContext(hProv: HCRYPTPROV, dwFlags: DWORD) -> BOOL;
 
  pub fn GetSystemTimeAsFileTime(lpSystemTimeAsFileTime: LPFILETIME);
 
@@ -1175,6 +1160,9 @@ extern "system" {
  writefds: *mut fd_set,
  exceptfds: *mut fd_set,
  timeout: *const timeval) -> c_int;
+
+ #[link_name = "SystemFunction036"]
+ pub fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: ULONG) -> BOOLEAN;
 }
 
 // Functions that aren't available on every version of Windows that we support,

src/libstd/sys/windows/rand.rs

@@ -14,25 +14,12 @@ use mem;
 use rand::Rng;
 use sys::c;
 
-pub struct OsRng {
- hcryptprov: c::HCRYPTPROV
-}
+pub struct OsRng;
 
 impl OsRng {
  /// Create a new `OsRng`.
  pub fn new() -> io::Result<OsRng> {
- let mut hcp = 0;
- let ret = unsafe {
- c::CryptAcquireContextA(&mut hcp, 0 as c::LPCSTR, 0 as c::LPCSTR,
- c::PROV_RSA_FULL,
- c::CRYPT_VERIFYCONTEXT | c::CRYPT_SILENT)
- };
-
- if ret == 0 {
- Err(io::Error::last_os_error())
- } else {
- Ok(OsRng { hcryptprov: hcp })
- }
+ Ok(OsRng)
  }
 }
 
@@ -42,18 +29,19 @@ impl Rng for OsRng {
  self.fill_bytes(&mut v);
  unsafe { mem::transmute(v) }
  }
+
  fn next_u64(&mut self) -> u64 {
  let mut v = [0; 8];
  self.fill_bytes(&mut v);
  unsafe { mem::transmute(v) }
  }
+
  fn fill_bytes(&mut self, v: &mut [u8]) {
- // CryptGenRandom takes a DWORD (u32) for the length so we need to
+ // RtlGenRandom takes an ULONG (u32) for the length so we need to
  // split up the buffer.
- for slice in v.chunks_mut(<c::DWORD>::max_value() as usize) {
+ for slice in v.chunks_mut(<c::ULONG>::max_value() as usize) {
  let ret = unsafe {
- c::CryptGenRandom(self.hcryptprov, slice.len() as c::DWORD,
- slice.as_mut_ptr())
+ c::RtlGenRandom(slice.as_mut_ptr(), slice.len() as c::ULONG)
  };
  if ret == 0 {
  panic!("couldn't generate random bytes: {}",
@@ -62,15 +50,3 @@ impl Rng for OsRng {
  }
  }
 }
-
-impl Drop for OsRng {
- fn drop(&mut self) {
- let ret = unsafe {
- c::CryptReleaseContext(self.hcryptprov, 0)
- };
- if ret == 0 {
- panic!("couldn't release context: {}",
- io::Error::last_os_error());
- }
- }
-}