From: Eric Biggers <ebigg...@google.com>
The arm64 implementations of ChaCha and XChaCha are failing the extra
crypto self-tests following my patches to test the !may_use_simd() code
paths, which previously were untested. The problem is as follows:
When !may_use_simd(), the arm64 NEON implementations fall back to the
generic implementation, which uses the skcipher_walk API to iterate
through the src/dst scatterlists. Due to how the skcipher_walk API
works, walk.stride is set from the skcipher_alg actually being used,
which in this case is the arm64 NEON algorithm. Thus walk.stride is
5*CHACHA_BLOCK_SIZE, not CHACHA_BLOCK_SIZE.
This unnecessarily large stride shouldn't cause an actual problem.
However, the generic implementation computes round_down(nbytes,
walk.stride). round_down() assumes the round amount is a power of 2,
which 5*CHACHA_BLOCK_SIZE is not, so it gives the wrong result.
This causes the following case in skcipher_walk_done() to be hit,
causing a WARN() and failing the encryption operation:
if (WARN_ON(err)) {
/* unexpected case; didn't process all bytes */
err = -EINVAL;
goto finish;
}
Fix it by rounding down to CHACHA_BLOCK_SIZE instead of walk.stride.
(Or we could replace round_down() with rounddown(), but that would add a
slow division operation every time, which I think we should avoid.)
Fixes: 2fe55987b262 ("crypto: arm64/chacha - use combined SIMD/ALU routine for
more speed")
Cc: <sta...@vger.kernel.org> # v5.0+
Signed-off-by: Eric Biggers <ebigg...@google.com>
---
crypto/chacha_generic.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/crypto/chacha_generic.c b/crypto/chacha_generic.c
index 35b583101f4f..90ec0ec1b4f7 100644
--- a/crypto/chacha_generic.c
+++ b/crypto/chacha_generic.c
@@ -52,7 +52,7 @@ static int chacha_stream_xor(struct skcipher_request *req,
unsigned int nbytes = walk.nbytes;
if (nbytes < walk.total)
- nbytes = round_down(nbytes, walk.stride);
+ nbytes = round_down(nbytes, CHACHA_BLOCK_SIZE);
chacha_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
nbytes, ctx->nrounds);
--
2.21.0
