crypto: chacha20 - Fix chacha20_block() keystream alignment (again)

In commit 9f480faec58c ("crypto: chacha20 - Fix keystream alignment for
chacha20_block()"), I had missed that chacha20_block() can be called
directly on the buffer passed to get_random_bytes(), which can have any
alignment.  So, while my commit didn't break anything, it didn't fully
solve the alignment problems.

Revert my solution and just update chacha20_block() to use
put_unaligned_le32(), so the output buffer need not be aligned.
This is simpler, and on many CPUs it's the same speed.

But, I kept the 'tmp' buffers in extract_crng_user() and
_get_random_bytes() 4-byte aligned, since that alignment is actually
needed for _crng_backtrack_protect() too.

Reported-by: Stephan Müller <smueller@chronox.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 4 insertions, 3 deletions

diff --git a/crypto/chacha20_generic.c b/crypto/chacha20_generic.c
index e451c3cb6a56..3ae96587caf9 100644
--- a/crypto/chacha20_generic.c
+++ b/crypto/chacha20_generic.c
@@ -18,20 +18,21 @@
 static void chacha20_docrypt(u32 *state, u8 *dst, const u8 *src,
                              unsigned int bytes)
 {
-        u32 stream[CHACHA20_BLOCK_WORDS];
+        /* aligned to potentially speed up crypto_xor() */
+        u8 stream[CHACHA20_BLOCK_SIZE] __aligned(sizeof(long));
 
         if (dst != src)
                 memcpy(dst, src, bytes);
 
         while (bytes >= CHACHA20_BLOCK_SIZE) {
                 chacha20_block(state, stream);
-                crypto_xor(dst, (const u8 *)stream, CHACHA20_BLOCK_SIZE);
+                crypto_xor(dst, stream, CHACHA20_BLOCK_SIZE);
                 bytes -= CHACHA20_BLOCK_SIZE;
                 dst += CHACHA20_BLOCK_SIZE;
         }
         if (bytes) {
                 chacha20_block(state, stream);
-                crypto_xor(dst, (const u8 *)stream, bytes);
+                crypto_xor(dst, stream, bytes);
         }
 }