On Tue Jan 2, 2024 at 7:03 PM EET, James Bottomley wrote: > From: Ard Biesheuvel <[email protected]> > > 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 <[email protected]> > Reviewed-by: James Bottomley <[email protected]> > Link: > https://lore.kernel.org/all/[email protected]/ > Signed-off-by: Ard Biesheuvel <[email protected]> > --- > 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 8d1446c2be71..969baab8c805 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 <[email protected]>"); > +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
Reviewed-by: Jarkko Sakkinen <[email protected]> BR, Jarkko
