// SPDX-License-Identifier: GPL-2.0
/*
 * Minimal library implementation of AES in CFB mode
 *
 * Copyright 2023 Google LLC
 */

#include <crypto/aes.h>
#include <crypto/algapi.h>
#include <linux/export.h>
#include <linux/module.h>
#include <asm/irqflags.h>

static void aescfb_encrypt_block(const struct aes_enckey *key, 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(key, dst, src);
        local_irq_restore(flags);
}

/**
 * aescfb_encrypt - Perform AES-CFB encryption on a block of data
 *
 * @key:        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 aes_enckey *key, 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(key, 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
 *
 * @key:        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 aes_enckey *key, u8 *dst, const u8 *src,
                    int len, const u8 iv[AES_BLOCK_SIZE])
{
        u8 ks[2][AES_BLOCK_SIZE];

        aescfb_encrypt_block(key, 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(key, 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");

#ifdef CONFIG_CRYPTO_SELFTESTS

/*
 * Test code below. Vectors taken from crypto/testmgr.h
 */

static struct {
        u8      ptext[64] __nonstring;
        u8      ctext[64] __nonstring;

        u8      key[AES_MAX_KEY_SIZE] __nonstring;
        u8      iv[AES_BLOCK_SIZE] __nonstring;

        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 aes_enckey key;
                u8 buf[64];

                if (aes_prepareenckey(&key, aescfb_tv[i].key, aescfb_tv[i].klen)) {
                        pr_err("aes_prepareenckey() failed on vector %d\n", i);
                        return -ENODEV;
                }

                aescfb_encrypt(&key, 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(&key, 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(&key, 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