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List: linux-keyrings
Subject: Re: [PATCH v4 01/13] crypto: lib - implement library version of AES in CFB mode
From: "Jarkko Sakkinen" <jarkko () kernel ! org>
Date: 2023-04-23 3:34:44
Message-ID: CS3TJ9U4JBC0.1N73X4N8VI3K () suppilovahvero
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On Tue Apr 4, 2023 at 12:39 AM EEST, James Bottomley wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
>
> 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@HansenPartnership.com>
> Reviewed-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> Link: https://lore.kernel.org/all/20230216201410.15010-1-James.Bottomley@HansenPartnership.com/
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> include/crypto/aes.h | 5 +
> lib/crypto/Kconfig | 5 +
> lib/crypto/Makefile | 3 +
> lib/crypto/aescfb.c | 257 +++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 270 insertions(+)
> create mode 100644 lib/crypto/aescfb.c
>
> diff --git a/include/crypto/aes.h b/include/crypto/aes.h
> index 2090729701ab..9339da7c20a8 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 45436bfc6dff..b01253cac70a 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 6ec2d4543d9c..33213a01aab1 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 000000000000..749dc1258a44
> --- /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@kernel.org>");
> +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
> --
> 2.35.3
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
BR, Jarkko
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