crypto: aes - Remove aes-fixed-time / CONFIG_CRYPTO_AES_TI

Remove aes-fixed-time, i.e. CONFIG_CRYPTO_AES_TI.  This was a wrapper
around the 256-byte-table-based AES implementation in lib/crypto/aes.c,
with extra code to enable and disable IRQs for constant-time hardening.

While nice in theory, in practice this had the following issues:

- For bulk en/decryption it was 2-4 times slower than aes-generic.  This
  resulted in aes-generic still being needed, creating fragmentation.

- Having both aes-generic and aes-fixed-time punted an AES
  implementation decision to distros and users who are generally
  unprepared to handle it.  In practice, whether aes-fixed-time gets
  used tends to be incidental and not match an explicit distro or user
  intent.  (While aes-fixed-time has a higher priority than aes-generic,
  whether it actually gets enabled, loaded, and used depends on the
  kconfig and whether a modprobe of "aes" happens to be done.  It also
  has a lower priority than aes-arm and aes-arm64.)

- My changes to the generic AES code (in other commits) significantly
  close the gap with aes-fixed-time anyway.  The table size is reduced
  from 8192 bytes to 1024 bytes, and prefetching is added.

- While AES code *should* be constant-time, the real solutions for that
  are AES instructions (which most CPUs have now) or bit-slicing.  arm
  and arm64 already have bit-sliced AES code for many modes; generic
  bit-sliced code could be written but would be very slow for single
  blocks.  Overall, I suggest that trying to write constant-time
  table-based AES code is a bit futile anyway, and in the rare cases
  where a proper AES implementation is still unavailable it's reasonable
  to compromise with an implementation that simply prefetches the table.

Thus, this commit removes aes-fixed-time and CONFIG_CRYPTO_AES_TI.  The
replacement is just the existing CONFIG_CRYPTO_AES, which for now maps
to the existing aes-generic code, but I'll soon be changing to use the
improved AES library code instead.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20260112192035.10427-9-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

3 files changed, 0 insertions, 105 deletions

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 443fe8e016fd..db6b0c2fb50e 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -366,27 +366,6 @@ config CRYPTO_AES
 
 	  The AES specifies three key sizes: 128, 192 and 256 bits
 
-config CRYPTO_AES_TI
-	tristate "AES (Advanced Encryption Standard) (fixed time)"
-	select CRYPTO_ALGAPI
-	select CRYPTO_LIB_AES
-	help
-	  AES cipher algorithms (Rijndael)(FIPS-197, ISO/IEC 18033-3)
-
-	  This is a generic implementation of AES that attempts to eliminate
-	  data dependent latencies as much as possible without affecting
-	  performance too much. It is intended for use by the generic CCM
-	  and GCM drivers, and other CTR or CMAC/XCBC based modes that rely
-	  solely on encryption (although decryption is supported as well, but
-	  with a more dramatic performance hit)
-
-	  Instead of using 16 lookup tables of 1 KB each, (8 for encryption and
-	  8 for decryption), this implementation only uses just two S-boxes of
-	  256 bytes each, and attempts to eliminate data dependent latencies by
-	  prefetching the entire table into the cache at the start of each
-	  block. Interrupts are also disabled to avoid races where cachelines
-	  are evicted when the CPU is interrupted to do something else.
-
 config CRYPTO_ANUBIS
 	tristate "Anubis"
 	depends on CRYPTO_USER_API_ENABLE_OBSOLETE
diff --git a/crypto/Makefile b/crypto/Makefile
index 23d3db7be425..be403dc20645 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -134,7 +134,6 @@ obj-$(CONFIG_CRYPTO_AES) += aes_generic.o
 CFLAGS_aes_generic.o := $(call cc-option,-fno-code-hoisting) # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
 obj-$(CONFIG_CRYPTO_SM4) += sm4.o
 obj-$(CONFIG_CRYPTO_SM4_GENERIC) += sm4_generic.o
-obj-$(CONFIG_CRYPTO_AES_TI) += aes_ti.o
 obj-$(CONFIG_CRYPTO_CAMELLIA) += camellia_generic.o
 obj-$(CONFIG_CRYPTO_CAST_COMMON) += cast_common.o
 obj-$(CONFIG_CRYPTO_CAST5) += cast5_generic.o
diff --git a/crypto/aes_ti.c b/crypto/aes_ti.c
deleted file mode 100644
index a3b342f92fab..000000000000
--- a/crypto/aes_ti.c
+++ /dev/null
@@ -1,83 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * Scalar fixed time AES core transform
- *
- * Copyright (C) 2017 Linaro Ltd <ard.biesheuvel@linaro.org>
- */
-
-#include <crypto/aes.h>
-#include <crypto/algapi.h>
-#include <linux/module.h>
-
-static int aesti_set_key(struct crypto_tfm *tfm, const u8 *in_key,
-			 unsigned int key_len)
-{
-	struct crypto_aes_ctx *ctx = crypto_tfm_ctx(tfm);
-
-	return aes_expandkey(ctx, in_key, key_len);
-}
-
-static void aesti_encrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
-{
-	const struct crypto_aes_ctx *ctx = crypto_tfm_ctx(tfm);
-	unsigned long flags;
-
-	/*
-	 * Temporarily disable interrupts to avoid races where cachelines are
-	 * evicted when the CPU is interrupted to do something else.
-	 */
-	local_irq_save(flags);
-
-	aes_encrypt(ctx, out, in);
-
-	local_irq_restore(flags);
-}
-
-static void aesti_decrypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
-{
-	const struct crypto_aes_ctx *ctx = crypto_tfm_ctx(tfm);
-	unsigned long flags;
-
-	/*
-	 * Temporarily disable interrupts to avoid races where cachelines are
-	 * evicted when the CPU is interrupted to do something else.
-	 */
-	local_irq_save(flags);
-
-	aes_decrypt(ctx, out, in);
-
-	local_irq_restore(flags);
-}
-
-static struct crypto_alg aes_alg = {
-	.cra_name			= "aes",
-	.cra_driver_name		= "aes-fixed-time",
-	.cra_priority			= 100 + 1,
-	.cra_flags			= CRYPTO_ALG_TYPE_CIPHER,
-	.cra_blocksize			= AES_BLOCK_SIZE,
-	.cra_ctxsize			= sizeof(struct crypto_aes_ctx),
-	.cra_module			= THIS_MODULE,
-
-	.cra_cipher.cia_min_keysize	= AES_MIN_KEY_SIZE,
-	.cra_cipher.cia_max_keysize	= AES_MAX_KEY_SIZE,
-	.cra_cipher.cia_setkey		= aesti_set_key,
-	.cra_cipher.cia_encrypt		= aesti_encrypt,
-	.cra_cipher.cia_decrypt		= aesti_decrypt
-};
-
-static int __init aes_init(void)
-{
-	return crypto_register_alg(&aes_alg);
-}
-
-static void __exit aes_fini(void)
-{
-	crypto_unregister_alg(&aes_alg);
-}
-
-module_init(aes_init);
-module_exit(aes_fini);
-
-MODULE_DESCRIPTION("Generic fixed time AES");
-MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
-MODULE_LICENSE("GPL v2");