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

Restore the SIMD usability check that was removed by commit 773426f4771b
("crypto: arm/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: 773426f4771b ("crypto: arm/poly1305 - Add block-only interface")
Cc: stable@vger.kernel.org
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250706231100.176113-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

diff --git a/lib/crypto/arm/poly1305-glue.c b/lib/crypto/arm/poly1305-glue.c
index 2603b0771f2c4c503543639c648f5d220b7e6d12..ca6dc553370546327953de1690acbdf536d7e046 100644 (file)
--- a/lib/crypto/arm/poly1305-glue.c
+++ b/lib/crypto/arm/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>
@@ -39,7 +40,7 @@ void poly1305_blocks_arch(struct poly1305_block_state *state, const u8 *src,
 {
        len = round_down(len, POLY1305_BLOCK_SIZE);
        if (IS_ENABLED(CONFIG_KERNEL_MODE_NEON) &&
-           static_branch_likely(&have_neon)) {
+           static_branch_likely(&have_neon) && likely(may_use_simd())) {
                do {
                        unsigned int todo = min_t(unsigned int, len, SZ_4K);