From 3e1e83fdd4be9d49f6ee9d75a36f1c3a25d59fc8 Mon Sep 17 00:00:00 2001
From: Joshua Liebow-Feeser <joshlf@users.noreply.github.com>
Date: Mon, 12 Feb 2024 19:19:10 -0800
Subject: [PATCH] aes: Assert precondition required for soundness (#407)

---
 aes/src/armv8/expand.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/aes/src/armv8/expand.rs b/aes/src/armv8/expand.rs
index 0a0eaa67..b4bfac8c 100644
--- a/aes/src/armv8/expand.rs
+++ b/aes/src/armv8/expand.rs
@@ -18,6 +18,9 @@ pub unsafe fn expand_key<const L: usize, const N: usize>(key: &[u8; L]) -> [uint
 
     let mut expanded_keys: [uint8x16_t; N] = mem::zeroed();
 
+    // Sanity check, as this is required in order for the following line to be sound.
+    // We'd rather panic than exhibit undefined behavior.
+    assert!(mem::align_of::<uint8x16_t>() >= mem::align_of::<u32>());
     let columns =
         slice::from_raw_parts_mut(expanded_keys.as_mut_ptr() as *mut u32, N * BLOCK_WORDS);