From 1ad40787ec88039f829144ef59b7bc506eaf07ed Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sat, 24 Aug 2024 11:28:39 -0600
Subject: [PATCH] cpufeatures: add support for DIT detection on Apple silicon
 (#1100)

Adds support for detecting Data Independent Timing (DIT) support which
is available on Apple silicon (e.g. M1/M2/M3).

This uses the `hw.optional.arm.FEAT_DIT` sysctl for detection.

For more information, see:

https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Enable-DIT-for-constant-time-cryptographic-operations
---
 cpufeatures/src/aarch64.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/cpufeatures/src/aarch64.rs b/cpufeatures/src/aarch64.rs
index 4248a754..58695532 100644
--- a/cpufeatures/src/aarch64.rs
+++ b/cpufeatures/src/aarch64.rs
@@ -107,6 +107,12 @@ macro_rules! check {
     ("aes") => {
         true
     };
+    ("dit") => {
+        // https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Enable-DIT-for-constant-time-cryptographic-operations
+        unsafe {
+            $crate::aarch64::sysctlbyname(b"hw.optional.arm.FEAT_DIT\0")
+        }
+    };
     ("sha2") => {
         true
     };