Implement AES in CFB mode using the existing, mostly constant-time generic AES library implementation. This will be used by the TPM code to encrypt communications with TPM hardware, which is often a discrete component connected using sniffable wires or traces. While a CFB template does exist, using a skcipher is a major pain for non-performance critical synchronous crypto where the algorithm is known at compile time and the data is in contiguous buffers with valid kernel virtual addresses. Tested-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> Reviewed-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/all/20230216201410.15010-1-James.Bottomley@xxxxxxxxxxxxxxxxxxxxx/ Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> --- v1 was sent out by James and is archived at the URL above v2: - add test cases and kerneldoc comments - add memzero_explicit() calls to wipe the keystream buffers - add module exports - add James's Tb/Rb include/crypto/aes.h | 5 + lib/crypto/Kconfig | 5 + lib/crypto/Makefile | 3 + lib/crypto/aescfb.c | 257 ++++++++++++++++++++ 4 files changed, 270 insertions(+) diff --git a/include/crypto/aes.h b/include/crypto/aes.h index 2090729701ab6d7a..9339da7c20a8b54e 100644 --- a/include/crypto/aes.h +++ b/include/crypto/aes.h @@ -87,4 +87,9 @@ void aes_decrypt(const struct crypto_aes_ctx *ctx, u8 *out, const u8 *in); extern const u8 crypto_aes_sbox[]; extern const u8 crypto_aes_inv_sbox[]; +void aescfb_encrypt(const struct crypto_aes_ctx *ctx, u8 *dst, const u8 *src, + int len, const u8 iv[AES_BLOCK_SIZE]); +void aescfb_decrypt(const struct crypto_aes_ctx *ctx, u8 *dst, const u8 *src, + int len, const u8 iv[AES_BLOCK_SIZE]); + #endif diff --git a/lib/crypto/Kconfig b/lib/crypto/Kconfig index 45436bfc6dffe1db..b01253cac70a7499 100644 --- a/lib/crypto/Kconfig +++ b/lib/crypto/Kconfig @@ -8,6 +8,11 @@ config CRYPTO_LIB_UTILS config CRYPTO_LIB_AES tristate +config CRYPTO_LIB_AESCFB + tristate + select CRYPTO_LIB_AES + select CRYPTO_LIB_UTILS + config CRYPTO_LIB_AESGCM tristate select CRYPTO_LIB_AES diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile index 6ec2d4543d9cad48..33213a01aab101e8 100644 --- a/lib/crypto/Makefile +++ b/lib/crypto/Makefile @@ -10,6 +10,9 @@ obj-$(CONFIG_CRYPTO_LIB_CHACHA_GENERIC) += libchacha.o obj-$(CONFIG_CRYPTO_LIB_AES) += libaes.o libaes-y := aes.o +obj-$(CONFIG_CRYPTO_LIB_AESCFB) += libaescfb.o +libaescfb-y := aescfb.o + obj-$(CONFIG_CRYPTO_LIB_AESGCM) += libaesgcm.o libaesgcm-y := aesgcm.o diff --git a/lib/crypto/aescfb.c b/lib/crypto/aescfb.c new file mode 100644 index 0000000000000000..749dc1258a44b7af --- /dev/null +++ b/lib/crypto/aescfb.c @@ -0,0 +1,257 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Minimal library implementation of AES in CFB mode + * + * Copyright 2023 Google LLC + */ + +#include <linux/module.h> + +#include <crypto/algapi.h> +#include <crypto/aes.h> + +#include <asm/irqflags.h> + +static void aescfb_encrypt_block(const struct crypto_aes_ctx *ctx, void *dst, + const void *src) +{ + unsigned long flags; + + /* + * In AES-CFB, the AES encryption operates on known 'plaintext' (the IV + * and ciphertext), making it susceptible to timing attacks on the + * encryption key. The AES library already mitigates this risk to some + * extent by pulling the entire S-box into the caches before doing any + * substitutions, but this strategy is more effective when running with + * interrupts disabled. + */ + local_irq_save(flags); + aes_encrypt(ctx, dst, src); + local_irq_restore(flags); +} + +/** + * aescfb_encrypt - Perform AES-CFB encryption on a block of data + * + * @ctx: The AES-CFB key schedule + * @dst: Pointer to the ciphertext output buffer + * @src: Pointer the plaintext (may equal @dst for encryption in place) + * @len: The size in bytes of the plaintext and ciphertext. + * @iv: The initialization vector (IV) to use for this block of data + */ +void aescfb_encrypt(const struct crypto_aes_ctx *ctx, u8 *dst, const u8 *src, + int len, const u8 iv[AES_BLOCK_SIZE]) +{ + u8 ks[AES_BLOCK_SIZE]; + const u8 *v = iv; + + while (len > 0) { + aescfb_encrypt_block(ctx, ks, v); + crypto_xor_cpy(dst, src, ks, min(len, AES_BLOCK_SIZE)); + v = dst; + + dst += AES_BLOCK_SIZE; + src += AES_BLOCK_SIZE; + len -= AES_BLOCK_SIZE; + } + + memzero_explicit(ks, sizeof(ks)); +} +EXPORT_SYMBOL(aescfb_encrypt); + +/** + * aescfb_decrypt - Perform AES-CFB decryption on a block of data + * + * @ctx: The AES-CFB key schedule + * @dst: Pointer to the plaintext output buffer + * @src: Pointer the ciphertext (may equal @dst for decryption in place) + * @len: The size in bytes of the plaintext and ciphertext. + * @iv: The initialization vector (IV) to use for this block of data + */ +void aescfb_decrypt(const struct crypto_aes_ctx *ctx, u8 *dst, const u8 *src, + int len, const u8 iv[AES_BLOCK_SIZE]) +{ + u8 ks[2][AES_BLOCK_SIZE]; + + aescfb_encrypt_block(ctx, ks[0], iv); + + for (int i = 0; len > 0; i ^= 1) { + if (len > AES_BLOCK_SIZE) + /* + * Generate the keystream for the next block before + * performing the XOR, as that may update in place and + * overwrite the ciphertext. + */ + aescfb_encrypt_block(ctx, ks[!i], src); + + crypto_xor_cpy(dst, src, ks[i], min(len, AES_BLOCK_SIZE)); + + dst += AES_BLOCK_SIZE; + src += AES_BLOCK_SIZE; + len -= AES_BLOCK_SIZE; + } + + memzero_explicit(ks, sizeof(ks)); +} +EXPORT_SYMBOL(aescfb_decrypt); + +MODULE_DESCRIPTION("Generic AES-CFB library"); +MODULE_AUTHOR("Ard Biesheuvel <ardb@xxxxxxxxxx>"); +MODULE_LICENSE("GPL"); + +#ifndef CONFIG_CRYPTO_MANAGER_DISABLE_TESTS + +/* + * Test code below. Vectors taken from crypto/testmgr.h + */ + +static struct { + u8 ptext[64]; + u8 ctext[64]; + + u8 key[AES_MAX_KEY_SIZE]; + u8 iv[AES_BLOCK_SIZE]; + + int klen; + int len; +} const aescfb_tv[] __initconst = { + { /* From NIST SP800-38A */ + .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" + "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", + .klen = 16, + .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" + "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", + .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" + "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" + "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" + "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" + "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" + "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" + "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" + "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", + .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20" + "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a" + "\xc8\xa6\x45\x37\xa0\xb3\xa9\x3f" + "\xcd\xe3\xcd\xad\x9f\x1c\xe5\x8b" + "\x26\x75\x1f\x67\xa3\xcb\xb1\x40" + "\xb1\x80\x8c\xf1\x87\xa4\xf4\xdf" + "\xc0\x4b\x05\x35\x7c\x5d\x1c\x0e" + "\xea\xc4\xc6\x6f\x9f\xf7\xf2\xe6", + .len = 64, + }, { + .key = "\x8e\x73\xb0\xf7\xda\x0e\x64\x52" + "\xc8\x10\xf3\x2b\x80\x90\x79\xe5" + "\x62\xf8\xea\xd2\x52\x2c\x6b\x7b", + .klen = 24, + .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" + "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", + .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" + "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" + "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" + "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" + "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" + "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" + "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" + "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", + .ctext = "\xcd\xc8\x0d\x6f\xdd\xf1\x8c\xab" + "\x34\xc2\x59\x09\xc9\x9a\x41\x74" + "\x67\xce\x7f\x7f\x81\x17\x36\x21" + "\x96\x1a\x2b\x70\x17\x1d\x3d\x7a" + "\x2e\x1e\x8a\x1d\xd5\x9b\x88\xb1" + "\xc8\xe6\x0f\xed\x1e\xfa\xc4\xc9" + "\xc0\x5f\x9f\x9c\xa9\x83\x4f\xa0" + "\x42\xae\x8f\xba\x58\x4b\x09\xff", + .len = 64, + }, { + .key = "\x60\x3d\xeb\x10\x15\xca\x71\xbe" + "\x2b\x73\xae\xf0\x85\x7d\x77\x81" + "\x1f\x35\x2c\x07\x3b\x61\x08\xd7" + "\x2d\x98\x10\xa3\x09\x14\xdf\xf4", + .klen = 32, + .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" + "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", + .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" + "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" + "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" + "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" + "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" + "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" + "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" + "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", + .ctext = "\xdc\x7e\x84\xbf\xda\x79\x16\x4b" + "\x7e\xcd\x84\x86\x98\x5d\x38\x60" + "\x39\xff\xed\x14\x3b\x28\xb1\xc8" + "\x32\x11\x3c\x63\x31\xe5\x40\x7b" + "\xdf\x10\x13\x24\x15\xe5\x4b\x92" + "\xa1\x3e\xd0\xa8\x26\x7a\xe2\xf9" + "\x75\xa3\x85\x74\x1a\xb9\xce\xf8" + "\x20\x31\x62\x3d\x55\xb1\xe4\x71", + .len = 64, + }, { /* > 16 bytes, not a multiple of 16 bytes */ + .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" + "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", + .klen = 16, + .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" + "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", + .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" + "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" + "\xae", + .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20" + "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a" + "\xc8", + .len = 17, + }, { /* < 16 bytes */ + .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" + "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", + .klen = 16, + .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" + "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", + .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f", + .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad", + .len = 7, + }, +}; + +static int __init libaescfb_init(void) +{ + for (int i = 0; i < ARRAY_SIZE(aescfb_tv); i++) { + struct crypto_aes_ctx ctx; + u8 buf[64]; + + if (aes_expandkey(&ctx, aescfb_tv[i].key, aescfb_tv[i].klen)) { + pr_err("aes_expandkey() failed on vector %d\n", i); + return -ENODEV; + } + + aescfb_encrypt(&ctx, buf, aescfb_tv[i].ptext, aescfb_tv[i].len, + aescfb_tv[i].iv); + if (memcmp(buf, aescfb_tv[i].ctext, aescfb_tv[i].len)) { + pr_err("aescfb_encrypt() #1 failed on vector %d\n", i); + return -ENODEV; + } + + /* decrypt in place */ + aescfb_decrypt(&ctx, buf, buf, aescfb_tv[i].len, aescfb_tv[i].iv); + if (memcmp(buf, aescfb_tv[i].ptext, aescfb_tv[i].len)) { + pr_err("aescfb_decrypt() failed on vector %d\n", i); + return -ENODEV; + } + + /* encrypt in place */ + aescfb_encrypt(&ctx, buf, buf, aescfb_tv[i].len, aescfb_tv[i].iv); + if (memcmp(buf, aescfb_tv[i].ctext, aescfb_tv[i].len)) { + pr_err("aescfb_encrypt() #2 failed on vector %d\n", i); + + return -ENODEV; + } + + } + return 0; +} +module_init(libaescfb_init); + +static void __exit libaescfb_exit(void) +{ +} +module_exit(libaescfb_exit); +#endif -- 2.39.1
