base/runtime: Add `rand_bytes` and `HAS_RAND_BYTES`

Having the OS/runtime provide a cryptographic entropy source is the
right thing to do, and we need it to initialize the default random
number generator.

10 files changed, 154 insertions, 1 deletions

diff --git a/base/runtime/os_specific.odin b/base/runtime/os_specific.odin
index b6c1288d0..16e7e4751 100644
--- a/base/runtime/os_specific.odin
+++ b/base/runtime/os_specific.odin
@@ -2,10 +2,20 @@ package runtime
 
 _OS_Errno :: distinct int
 
+HAS_RAND_BYTES :: _HAS_RAND_BYTES
+
 stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	return _stderr_write(data)
 }
 
+rand_bytes :: proc "contextless" (dst: []byte) {
+	when HAS_RAND_BYTES {
+		_rand_bytes(dst)
+	} else {
+		panic_contextless("base/runtime: no runtime entropy source")
+	}
+}
+
 exit :: proc "contextless" (code: int) -> ! {
 	_exit(code)
 }
\ No newline at end of file
diff --git a/base/runtime/os_specific_bsd.odin b/base/runtime/os_specific_bsd.odin
index de300f1e0..ab8eabb6c 100644
--- a/base/runtime/os_specific_bsd.odin
+++ b/base/runtime/os_specific_bsd.odin
@@ -4,6 +4,8 @@ package runtime
 
 foreign import libc "system:c"
 
+_HAS_RAND_BYTES :: true
+
 @(default_calling_convention="c")
 foreign libc {
 	@(link_name="write")
@@ -14,6 +16,8 @@ foreign libc {
 	} else {
 		__error :: proc() -> ^i32 ---
 	}
+
+	arc4random_buf :: proc(buf: [^]byte, nbytes: uint) ---
 }
 
 _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
@@ -25,6 +29,10 @@ _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	return int(ret), 0
 }
 
+_rand_bytes :: proc "contextless" (dst: []byte) {
+	arc4random_buf(raw_data(dst), len(dst))
+}
+
 _exit :: proc "contextless" (code: int) -> ! {
 	@(default_calling_convention="c")
 	foreign libc {
diff --git a/base/runtime/os_specific_darwin.odin b/base/runtime/os_specific_darwin.odin
index 37315240f..576725a1c 100644
--- a/base/runtime/os_specific_darwin.odin
+++ b/base/runtime/os_specific_darwin.odin
@@ -4,6 +4,8 @@ package runtime
 
 import "base:intrinsics"
 
+_HAS_RAND_BYTES :: true
+
 _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	STDERR :: 2
 	when ODIN_NO_CRT {
@@ -29,6 +31,18 @@ _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 
 foreign import libc "system:System"
 
+_rand_bytes :: proc "contextless" (dst: []byte) {
+	// This process used to use Security/RandomCopyBytes, however
+	// on every version of MacOS (>= 10.12) that we care about,
+	// arc4random is implemented securely.
+
+	@(default_calling_convention="c")
+	foreign libc {
+		arc4random_buf :: proc(buf: [^]byte, nbytes: uint) ---
+	}
+	arc4random_buf(raw_data(dst), len(dst))
+}
+
 _exit :: proc "contextless" (code: int) -> ! {
 	@(default_calling_convention="c")
 	foreign libc {
diff --git a/base/runtime/os_specific_freestanding.odin b/base/runtime/os_specific_freestanding.odin
index b5a5fb146..3b2b5a714 100644
--- a/base/runtime/os_specific_freestanding.odin
+++ b/base/runtime/os_specific_freestanding.odin
@@ -2,6 +2,8 @@
 #+private
 package runtime
 
+_HAS_RAND_BYTES :: false
+
 // TODO(bill): reimplement `os.write`
 _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	return 0, -1
diff --git a/base/runtime/os_specific_haiku.odin b/base/runtime/os_specific_haiku.odin
index 74ff58cde..7e53539a1 100644
--- a/base/runtime/os_specific_haiku.odin
+++ b/base/runtime/os_specific_haiku.odin
@@ -4,11 +4,15 @@ package runtime
 
 foreign import libc "system:c"
 
+_HAS_RAND_BYTES :: true
+
 foreign libc {
 	@(link_name="write")
 	_unix_write :: proc(fd: i32, buf: rawptr, size: int) -> int ---
 
 	_errnop :: proc() -> ^i32 ---
+
+	arc4random_buf :: proc(buf: [^]byte, nbytes: uint) ---
 }
 
 _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
@@ -20,7 +24,9 @@ _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	return int(ret), 0
 }
 
-
+_rand_bytes :: proc "contextless" (dst: []byte) {
+	arc4random_buf(raw_data(dst), len(dst))
+}
 
 _exit :: proc "contextless" (code: int) -> ! {
 	trap()
diff --git a/base/runtime/os_specific_js.odin b/base/runtime/os_specific_js.odin
index bd88b1871..8676f3a6e 100644
--- a/base/runtime/os_specific_js.odin
+++ b/base/runtime/os_specific_js.odin
@@ -4,6 +4,8 @@ package runtime
 
 foreign import "odin_env"
 
+_HAS_RAND_BYTES :: true
+
 _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	foreign odin_env {
 		write :: proc "contextless" (fd: u32, p: []byte) ---
@@ -12,6 +14,22 @@ _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	return len(data), 0
 }
 
+_rand_bytes :: proc "contextless" (dst: []byte) {
+	foreign odin_env {
+		@(link_name = "rand_bytes")
+		env_rand_bytes :: proc "contextless" (buf: []byte) ---
+	}
+
+	MAX_PER_CALL_BYTES :: 65536 // 64kiB
+
+	dst := dst
+	for len(dst) > 0 {
+		to_read := min(len(dst), MAX_PER_CALL_BYTES)
+		env_rand_bytes(dst[:to_read])
+
+		dst = dst[to_read:]
+	}
+}
 
 _exit :: proc "contextless" (code: int) -> ! {
 	trap()
diff --git a/base/runtime/os_specific_linux.odin b/base/runtime/os_specific_linux.odin
index dfe3c8841..1abcc03e5 100644
--- a/base/runtime/os_specific_linux.odin
+++ b/base/runtime/os_specific_linux.odin
@@ -3,6 +3,8 @@ package runtime
 
 import "base:intrinsics"
 
+_HAS_RAND_BYTES :: true
+
 _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	when ODIN_ARCH == .amd64 {
 		SYS_write :: uintptr(1)
@@ -25,6 +27,53 @@ _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	return ret, 0
 }
 
+_rand_bytes :: proc "contextless" (dst: []byte) {
+	when ODIN_ARCH == .amd64 {
+		SYS_getrandom :: uintptr(318)
+	} else when ODIN_ARCH == .arm64 {
+		SYS_getrandom :: uintptr(278)
+	} else when ODIN_ARCH == .i386 {
+		SYS_getrandom :: uintptr(355)
+	} else when ODIN_ARCH == .arm32 {
+		SYS_getrandom :: uintptr(384)
+	} else when ODIN_ARCH == .riscv64 {
+		SYS_getrandom :: uintptr(278)
+	} else {
+		#panic("base/runtime: no SYS_getrandom definition for target")
+	}
+
+	ERR_EINTR :: 4
+	ERR_ENOSYS :: 38
+
+	MAX_PER_CALL_BYTES :: 33554431 // 2^25 - 1
+
+	dst := dst
+	l := len(dst)
+
+	for l > 0 {
+		to_read := min(l, MAX_PER_CALL_BYTES)
+		ret := int(intrinsics.syscall(SYS_getrandom, uintptr(raw_data(dst[:to_read])), uintptr(to_read), uintptr(0)))
+		switch ret {
+		case -ERR_EINTR:
+			// Call interupted by a signal handler, just retry the
+			// request.
+			continue
+		case -ERR_ENOSYS:
+			// The kernel is apparently prehistoric (< 3.17 circa 2014)
+			// and does not support getrandom.
+			panic_contextless("base/runtime: getrandom not available in kernel")
+		case:
+			if ret < 0 {
+				// All other failures are things that should NEVER happen
+				// unless the kernel interface changes (ie: the Linux
+				// developers break userland).
+				panic_contextless("base/runtime: getrandom failed")
+			}
+		}
+		l -= ret
+		dst = dst[ret:]
+	}
+}
 
 _exit :: proc "contextless" (code: int) -> ! {
 	SYS_exit_group ::
diff --git a/base/runtime/os_specific_orca.odin b/base/runtime/os_specific_orca.odin
index 491edcfa4..f5ce50411 100644
--- a/base/runtime/os_specific_orca.odin
+++ b/base/runtime/os_specific_orca.odin
@@ -4,6 +4,8 @@ package runtime
 
 import "base:intrinsics"
 
+_HAS_RAND_BYTES :: false
+
 // Constants allowing to specify the level of logging verbosity.
 log_level :: enum u32 {
 	// Only errors are logged.
diff --git a/base/runtime/os_specific_wasi.odin b/base/runtime/os_specific_wasi.odin
index 194034865..c5e94653a 100644
--- a/base/runtime/os_specific_wasi.odin
+++ b/base/runtime/os_specific_wasi.odin
@@ -4,6 +4,8 @@ package runtime
 
 foreign import wasi "wasi_snapshot_preview1"
 
+_HAS_RAND_BYTES :: true
+
 @(default_calling_convention="contextless")
 foreign wasi {
 	fd_write :: proc(
@@ -26,6 +28,9 @@ foreign wasi {
 
 	@(private="file")
 	proc_exit :: proc(rval: u32) -> ! ---
+
+	@(private ="file")
+	random_get :: proc(buf: []u8) -> u16 ---
 }
 
 _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
@@ -34,6 +39,12 @@ _stderr_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
 	return int(n), _OS_Errno(err)
 }
 
+_rand_bytes :: proc "contextless" (dst: []byte) {
+	if errno := random_get(dst); errno != 0 {
+		panic_contextless("base/runtime: wasi.random_get failed")
+	}
+}
+
 _wasi_setup_args :: proc() {
 	num_of_args, size_of_args: uint
 	if errno := args_sizes_get(&num_of_args, &size_of_args); errno != 0 {
diff --git a/base/runtime/os_specific_windows.odin b/base/runtime/os_specific_windows.odin
index c5ca1e4c5..d938e87ea 100644
--- a/base/runtime/os_specific_windows.odin
+++ b/base/runtime/os_specific_windows.odin
@@ -2,8 +2,11 @@
 #+private
 package runtime
 
+foreign import bcrypt "system:Bcrypt.lib"
 foreign import kernel32 "system:Kernel32.lib"
 
+_HAS_RAND_BYTES :: true
+
 @(private="file")
 @(default_calling_convention="system")
 foreign kernel32 {
@@ -18,6 +21,12 @@ foreign kernel32 {
 	ExitProcess          :: proc(code: u32) -> ! ---
 }
 
+@(private="file")
+@(default_calling_convention="system")
+foreign bcrypt {
+	BCryptGenRandom :: proc(hAlgorithm: rawptr, pBuffer: [^]u8, cbBuffer: u32, dwFlags: u32) -> i32 ---
+}
+
 _stderr_write :: proc "contextless" (data: []byte) -> (n: int, err: _OS_Errno) #no_bounds_check {
 	if len(data) == 0 {
 		return 0, 0
@@ -52,6 +61,30 @@ _stderr_write :: proc "contextless" (data: []byte) -> (n: int, err: _OS_Errno) #
 	return
 }
 
+_rand_bytes :: proc "contextless" (dst: []byte) {
+	ensure_contextless(u64(len(dst)) <= u64(max(u32)), "base/runtime: oversized rand_bytes request")
+
+	BCRYPT_USE_SYSTEM_PREFERRED_RNG :: 0x00000002
+
+	ERROR_INVALID_HANDLE :: 6
+	ERROR_INVALID_PARAMETER :: 87
+
+	ret := BCryptGenRandom(nil, raw_data(dst), u32(len(dst)), BCRYPT_USE_SYSTEM_PREFERRED_RNG)
+	switch ret {
+	case 0:
+	case ERROR_INVALID_HANDLE:
+		// The handle to the first parameter is invalid.
+		// This should not happen here, since we explicitly pass nil to it
+		panic_contextless("base/runtime: BCryptGenRandom Invalid handle for hAlgorithm")
+	case ERROR_INVALID_PARAMETER:
+		// One of the parameters was invalid
+		panic_contextless("base/runtime: BCryptGenRandom Invalid parameter")
+	case:
+		// Unknown error
+		panic_contextless("base/runtime: BCryptGenRandom failed")
+	}
+}
+
 _exit :: proc "contextless" (code: int) -> ! {
 	ExitProcess(u32(code))
 }
\ No newline at end of file