libstd: windows: Use BCryptGenRandom on UWP

Since RtlGenRandom isn't available

Author: chouquette

src/libstd/build.rs

@@ -46,6 +46,8 @@ fn main() {
         println!("cargo:rustc-link-lib=userenv");
     } else if target.contains("uwp") {
         println!("cargo:rustc-link-lib=ws2_32");
+        // For BCryptGenRandom
+        println!("cargo:rustc-link-lib=bcrypt");
     } else if target.contains("fuchsia") {
         println!("cargo:rustc-link-lib=zircon");
         println!("cargo:rustc-link-lib=fdio");

src/libstd/sys/windows/c.rs

@@ -321,6 +321,9 @@ pub const STACK_SIZE_PARAM_IS_A_RESERVATION: DWORD = 0x00010000;
 
 pub const HEAP_ZERO_MEMORY: DWORD = 0x00000008;
 
+#[cfg(target_os = "uwp")]
+pub const BCRYPT_USE_SYSTEM_PREFERRED_RNG: DWORD = 0x00000002;
+
 #[repr(C)]
 #[cfg(not(target_pointer_width = "64"))]
 pub struct WSADATA {
@@ -1323,8 +1326,13 @@ extern "system" {
                   timeout: *const timeval) -> c_int;
 
     #[link_name = "SystemFunction036"]
+    #[cfg(not(target_os = "uwp"))]
     pub fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: ULONG) -> BOOLEAN;
 
+    #[cfg(target_os = "uwp")]
+    pub fn BCryptGenRandom(hAlgorithm: LPVOID, pBuffer: *mut u8,
+                           cbBuffer: ULONG, dwFlags: ULONG) -> LONG;
+
     pub fn GetProcessHeap() -> HANDLE;
     pub fn HeapAlloc(hHeap: HANDLE, dwFlags: DWORD, dwBytes: SIZE_T) -> LPVOID;
     pub fn HeapReAlloc(hHeap: HANDLE, dwFlags: DWORD, lpMem: LPVOID, dwBytes: SIZE_T) -> LPVOID;

src/libstd/sys/windows/rand.rs

@@ -1,7 +1,10 @@
 use crate::io;
 use crate::mem;
+#[cfg(target_os = "uwp")]
+use crate::ptr;
 use crate::sys::c;
 
+#[cfg(not(target_os = "uwp"))]
 pub fn hashmap_random_keys() -> (u64, u64) {
     let mut v = (0, 0);
     let ret = unsafe {
@@ -14,3 +17,18 @@ pub fn hashmap_random_keys() -> (u64, u64) {
     }
     return v
 }
+
+#[cfg(target_os = "uwp")]
+pub fn hashmap_random_keys() -> (u64, u64) {
+    let mut v = (0, 0);
+    let ret = unsafe {
+        c::BCryptGenRandom(ptr::null_mut(), &mut v as *mut _ as *mut u8,
+                           mem::size_of_val(&v) as c::ULONG,
+                           c::BCRYPT_USE_SYSTEM_PREFERRED_RNG)
+    };
+    if ret != 0 {
+        panic!("couldn't generate random bytes: {}",
+               io::Error::last_os_error());
+    }
+    return v
+}