lib/crypto: arm64/poly1305: Fix register corruption in no-SIMD contexts

Restore the SIMD usability check that was removed by commit a59e5468a921
("crypto: arm64/poly1305 - Add block-only interface").

This safety check is cheap and is well worth eliminating a footgun.
While the Poly1305 functions should not be called when SIMD registers
are unusable, if they are anyway, they should just do the right thing
instead of corrupting random tasks' registers and/or computing incorrect
MACs.  Fixing this is also needed for poly1305_kunit to pass.

Just use may_use_simd() instead of the original crypto_simd_usable(),
since poly1305_kunit won't rely on crypto_simd_disabled_for_test.

Fixes: a59e5468a921 ("crypto: arm64/poly1305 - Add block-only interface")
Cc: stable@vger.kernel.org
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250706231100.176113-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

diff --git a/lib/crypto/arm64/poly1305-glue.c b/lib/crypto/arm64/poly1305-glue.c
index c9a74766785bd7b4412640f1b7e996f9ff3df6db..31aea21ce42f79e08e4e028229deaebf61eab07b 100644 (file)
--- a/lib/crypto/arm64/poly1305-glue.c
+++ b/lib/crypto/arm64/poly1305-glue.c
@@ -7,6 +7,7 @@
 
 #include <asm/hwcap.h>
 #include <asm/neon.h>
+#include <asm/simd.h>
 #include <crypto/internal/poly1305.h>
 #include <linux/cpufeature.h>
 #include <linux/jump_label.h>
@@ -33,7 +34,7 @@ void poly1305_blocks_arch(struct poly1305_block_state *state, const u8 *src,
                          unsigned int len, u32 padbit)
 {
        len = round_down(len, POLY1305_BLOCK_SIZE);
-       if (static_branch_likely(&have_neon)) {
+       if (static_branch_likely(&have_neon) && likely(may_use_simd())) {
                do {
                        unsigned int todo = min_t(unsigned int, len, SZ_4K);