Hi Ard, On Fri, Oct 19, 2018 at 10:34:41PM +0800, Ard Biesheuvel wrote: > > diff --git a/include/crypto/chacha.h b/include/crypto/chacha.h > > index ae79e9983c72f..3d261f5cd156d 100644 > > --- a/include/crypto/chacha.h > > +++ b/include/crypto/chacha.h > > @@ -5,6 +5,11 @@ > > * XChaCha extends ChaCha's nonce to 192 bits, while provably retaining ChaCha's > > * security. Here they share the same key size, tfm context, and setkey > > * function; only their IV size and encrypt/decrypt function differ. > > + * > > + * The ChaCha paper specifies 20, 12, and 8-round variants. In general, it is > > + * recommended to use the 20-round variant ChaCha20. However, the other > > + * variants can be needed in some performance-sensitive scenarios. The generic > > + * ChaCha code currently allows only the 20 and 12-round variants. > > */ > > > > #ifndef _CRYPTO_CHACHA_H > > @@ -39,6 +44,8 @@ void crypto_chacha_init(u32 *state, struct chacha_ctx *ctx, u8 *iv); > > > > int crypto_chacha20_setkey(struct crypto_skcipher *tfm, const u8 *key, > > unsigned int keysize); > > +int crypto_chacha12_setkey(struct crypto_skcipher *tfm, const u8 *key, > > + unsigned int keysize); > > > > int crypto_chacha_crypt(struct skcipher_request *req); > > int crypto_xchacha_crypt(struct skcipher_request *req); > > diff --git a/lib/chacha.c b/lib/chacha.c > > index 0a2c2e5b7b84d..c4d69a83fcd2d 100644 > > --- a/lib/chacha.c > > +++ b/lib/chacha.c > > @@ -21,7 +21,7 @@ static void chacha_permute(u32 *x, int nrounds) > > int i; > > > > /* whitelist the allowed round counts */ > > - BUG_ON(nrounds != 20); > > + BUG_ON(nrounds != 20 && nrounds != 12); > > > > I didn't spot this until this patch, but BUG_ON() may bring down the > kernel, and so it should really only be used as a last resort. (i.e., > if this is called from non-process context things may explode rather > painfully) > > I didn't look at the entire file [which is a bit cumbersome while > reviewing incremental changes like this] and so I don't really have > another suggestion right now, but please try to come up with something > better if you can. > I'll change it to WARN_ON_ONCE(), I guess. I do still want it to be very noisy if something fishy is going on with the round count. - Eric
