All ciphers implemented in Linux have a block size less than or equal to 16 bytes and the most demanding hw require 16 bits alignment for the block buffer. We avoid 2 VLAs[1] by always allocating 16 bytes with 16 bits alignment, unless the architecture support efficient unaligned accesses. We also check, at runtime, that our assumptions still stand, possibly dynamically allocating a new buffer, just in case something changes in the future.
[1] https://lkml.org/lkml/2018/3/7/621 Signed-off-by: Salvatore Mesoraca <s.mesorac...@gmail.com> --- Notes: Can we maybe skip the runtime check? crypto/ctr.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 42 insertions(+), 8 deletions(-) diff --git a/crypto/ctr.c b/crypto/ctr.c index 854d924..f37adf0 100644 --- a/crypto/ctr.c +++ b/crypto/ctr.c @@ -35,6 +35,16 @@ struct crypto_rfc3686_req_ctx { struct skcipher_request subreq CRYPTO_MINALIGN_ATTR; }; +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS +#define DECLARE_CIPHER_BUFFER(name) u8 name[16] +#else +#define DECLARE_CIPHER_BUFFER(name) u8 __aligned(16) name[16] +#endif + +#define CHECK_CIPHER_BUFFER(name, size, align) \ + likely(size <= sizeof(name) && \ + name == PTR_ALIGN(((u8 *) name), align + 1)) + static int crypto_ctr_setkey(struct crypto_tfm *parent, const u8 *key, unsigned int keylen) { @@ -52,22 +62,35 @@ static int crypto_ctr_setkey(struct crypto_tfm *parent, const u8 *key, return err; } -static void crypto_ctr_crypt_final(struct blkcipher_walk *walk, - struct crypto_cipher *tfm) +static int crypto_ctr_crypt_final(struct blkcipher_walk *walk, + struct crypto_cipher *tfm) { unsigned int bsize = crypto_cipher_blocksize(tfm); unsigned long alignmask = crypto_cipher_alignmask(tfm); u8 *ctrblk = walk->iv; - u8 tmp[bsize + alignmask]; - u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1); u8 *src = walk->src.virt.addr; u8 *dst = walk->dst.virt.addr; unsigned int nbytes = walk->nbytes; + DECLARE_CIPHER_BUFFER(tmp); + u8 *keystream, *tmp2; + + if (CHECK_CIPHER_BUFFER(tmp, bsize, alignmask)) + keystream = tmp; + else { + tmp2 = kmalloc(bsize + alignmask, GFP_ATOMIC); + if (!tmp2) + return -ENOMEM; + keystream = PTR_ALIGN(tmp2 + 0, alignmask + 1); + } crypto_cipher_encrypt_one(tfm, keystream, ctrblk); crypto_xor_cpy(dst, keystream, src, nbytes); crypto_inc(ctrblk, bsize); + + if (unlikely(keystream != tmp)) + kfree(tmp2); + return 0; } static int crypto_ctr_crypt_segment(struct blkcipher_walk *walk, @@ -106,8 +129,17 @@ static int crypto_ctr_crypt_inplace(struct blkcipher_walk *walk, unsigned int nbytes = walk->nbytes; u8 *ctrblk = walk->iv; u8 *src = walk->src.virt.addr; - u8 tmp[bsize + alignmask]; - u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1); + DECLARE_CIPHER_BUFFER(tmp); + u8 *keystream, *tmp2; + + if (CHECK_CIPHER_BUFFER(tmp, bsize, alignmask)) + keystream = tmp; + else { + tmp2 = kmalloc(bsize + alignmask, GFP_ATOMIC); + if (!tmp2) + return -ENOMEM; + keystream = PTR_ALIGN(tmp2 + 0, alignmask + 1); + } do { /* create keystream */ @@ -120,6 +152,8 @@ static int crypto_ctr_crypt_inplace(struct blkcipher_walk *walk, src += bsize; } while ((nbytes -= bsize) >= bsize); + if (unlikely(keystream != tmp)) + kfree(tmp2); return nbytes; } @@ -147,8 +181,8 @@ static int crypto_ctr_crypt(struct blkcipher_desc *desc, } if (walk.nbytes) { - crypto_ctr_crypt_final(&walk, child); - err = blkcipher_walk_done(desc, &walk, 0); + err = crypto_ctr_crypt_final(&walk, child); + err = blkcipher_walk_done(desc, &walk, err); } return err; -- 1.9.1
