From 641e70563ac1cc498b31f4016c1f5dde8e0e4d71 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 12 Jan 2026 11:20:06 -0800 Subject: 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 Link: https://lore.kernel.org/r/20260112192035.10427-9-ebiggers@kernel.org Signed-off-by: Eric Biggers --- crypto/Kconfig | 21 --------------- crypto/Makefile | 1 - crypto/aes_ti.c | 83 --------------------------------------------------------- 3 files changed, 105 deletions(-) delete mode 100644 crypto/aes_ti.c (limited to 'crypto') 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 - */ - -#include -#include -#include - -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 "); -MODULE_LICENSE("GPL v2"); -- cgit v1.2.3