Re: [PATCH] crypto: xts - consolidate sanity check for keys

[Stephan Mueller <smueller@chronox.de>]

Am Sonntag, 7. Februar 2016, 14:41:22 schrieb Ard Biesheuvel:

Hi Ard,

> Hi Stephan,
> 
> On 7 February 2016 at 14:05, Stephan Mueller <smueller@chronox.de> wrote:
> > Hi,
> > 
> > I only have an x86 system for testing. May I ask the owners for the other
> > architectures to review and test?
> > 
> > ---8<---
> > 
> > The patch centralizes the XTS key check logic into the service function
> > xts_check_key which is invoked from the different XTS implementations.
> > With this, the XTS implementations in ARM, ARM64, PPC and S390 have now
> > a sanity check for the XTS keys similar to the other arches.
> > 
> > In addition, this service function received a check to ensure that the
> > key != the tweak key which is mandated by FIPS 140-2 IG A.9. As the
> > check is not present in the standards defining XTS, it is only enforced
> > in FIPS mode of the kernel.
> > 
> > Signed-off-by: Stephan Mueller <smueller@chronox.de>
> 
> One remark below (and a nit). With that fixed:
> 
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Thank you.
> 
> > ---
> > 
> >  arch/arm/crypto/aes-ce-glue.c       |  4 ++++
> >  arch/arm/crypto/aesbs-glue.c        |  5 +++++
> >  arch/arm64/crypto/aes-glue.c        |  4 ++++
> >  arch/powerpc/crypto/aes-spe-glue.c  |  5 +++++
> >  arch/s390/crypto/aes_s390.c         |  5 +++++
> >  arch/x86/crypto/aesni-intel_glue.c  | 11 +++--------
> >  arch/x86/crypto/camellia_glue.c     | 10 +++-------
> >  arch/x86/crypto/cast6_avx_glue.c    | 10 +++-------
> >  arch/x86/crypto/serpent_avx_glue.c  | 11 +++--------
> >  arch/x86/crypto/serpent_sse2_glue.c | 11 +++--------
> >  arch/x86/crypto/twofish_glue_3way.c | 10 +++-------
> >  crypto/xts.c                        | 11 +++--------
> >  include/crypto/xts.h                | 29 +++++++++++++++++++++++++++++
> >  13 files changed, 73 insertions(+), 53 deletions(-)
> > 
> > diff --git a/arch/arm/crypto/aes-ce-glue.c b/arch/arm/crypto/aes-ce-glue.c
> > index b445a5d..85ff69b 100644
> > --- a/arch/arm/crypto/aes-ce-glue.c
> > +++ b/arch/arm/crypto/aes-ce-glue.c
> > @@ -152,6 +152,10 @@ static int xts_set_key(struct crypto_tfm *tfm, const
> > u8 *in_key,> 
> >         struct crypto_aes_xts_ctx *ctx = crypto_tfm_ctx(tfm);
> >         int ret;
> > 
> > +       ret = xts_check_key(tfm, in_key, key_len);
> > +       if (ret)
> > +               return ret;
> > +
> > 
> >         ret = ce_aes_expandkey(&ctx->key1, in_key, key_len / 2);
> >         if (!ret)
> >         
> >                 ret = ce_aes_expandkey(&ctx->key2, &in_key[key_len / 2],
> > 
> > diff --git a/arch/arm/crypto/aesbs-glue.c b/arch/arm/crypto/aesbs-glue.c
> > index 6d68529..d004bd1 100644
> > --- a/arch/arm/crypto/aesbs-glue.c
> > +++ b/arch/arm/crypto/aesbs-glue.c
> > @@ -89,6 +89,11 @@ static int aesbs_xts_set_key(struct crypto_tfm *tfm,
> > const u8 *in_key,> 
> >  {
> >  
> >         struct aesbs_xts_ctx *ctx = crypto_tfm_ctx(tfm);
> >         int bits = key_len * 4;
> > 
> > +       int err;
> > +
> > +       err = xts_check_key(tfm, in_key, key_len);
> > +       if (err)
> > +               return err;
> > 
> >         if (private_AES_set_encrypt_key(in_key, bits, &ctx->enc.rk)) {
> >         
> >                 tfm->crt_flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > 
> > diff --git a/arch/arm64/crypto/aes-glue.c b/arch/arm64/crypto/aes-glue.c
> > index 05d9e16..c963d75 100644
> > --- a/arch/arm64/crypto/aes-glue.c
> > +++ b/arch/arm64/crypto/aes-glue.c
> > @@ -85,6 +85,10 @@ static int xts_set_key(struct crypto_tfm *tfm, const u8
> > *in_key,> 
> >         struct crypto_aes_xts_ctx *ctx = crypto_tfm_ctx(tfm);
> >         int ret;
> > 
> > +       ret = xts_check_key(tfm, in_key, key_len);
> > +       if (ret)
> > +               return ret;
> > +
> > 
> >         ret = aes_expandkey(&ctx->key1, in_key, key_len / 2);
> >         if (!ret)
> >         
> >                 ret = aes_expandkey(&ctx->key2, &in_key[key_len / 2],
> > 
> > diff --git a/arch/powerpc/crypto/aes-spe-glue.c
> > b/arch/powerpc/crypto/aes-spe-glue.c index 93ee046..1608079 100644
> > --- a/arch/powerpc/crypto/aes-spe-glue.c
> > +++ b/arch/powerpc/crypto/aes-spe-glue.c
> > @@ -126,6 +126,11 @@ static int ppc_xts_setkey(struct crypto_tfm *tfm,
> > const u8 *in_key,> 
> >                    unsigned int key_len)
> >  
> >  {
> >  
> >         struct ppc_xts_ctx *ctx = crypto_tfm_ctx(tfm);
> > 
> > +       int err;
> > +
> > +       err = xts_check_key(tfm, in_key, key_len);
> > +       if (err)
> > +               return err;
> > 
> >         key_len >>= 1;
> > 
> > diff --git a/arch/s390/crypto/aes_s390.c b/arch/s390/crypto/aes_s390.c
> > index 0b9b95f..3f1a1a4 100644
> > --- a/arch/s390/crypto/aes_s390.c
> > +++ b/arch/s390/crypto/aes_s390.c
> > @@ -587,6 +587,11 @@ static int xts_aes_set_key(struct crypto_tfm *tfm,
> > const u8 *in_key,> 
> >  {
> >  
> >         struct s390_xts_ctx *xts_ctx = crypto_tfm_ctx(tfm);
> >         u32 *flags = &tfm->crt_flags;
> > 
> > +       int err;
> > +
> > +       err = xts_check_key(tfm, in_key, key_len);
> > +       if (err)
> > +               return err;
> > 
> >         switch (key_len) {
> > 
> >         case 32:
> > diff --git a/arch/x86/crypto/aesni-intel_glue.c
> > b/arch/x86/crypto/aesni-intel_glue.c index 3633ad6..064c7e2 100644
> > --- a/arch/x86/crypto/aesni-intel_glue.c
> > +++ b/arch/x86/crypto/aesni-intel_glue.c
> > @@ -639,16 +639,11 @@ static int xts_aesni_setkey(struct crypto_tfm *tfm,
> > const u8 *key,> 
> >                             unsigned int keylen)
> >  
> >  {
> >  
> >         struct aesni_xts_ctx *ctx = crypto_tfm_ctx(tfm);
> > 
> > -       u32 *flags = &tfm->crt_flags;
> > 
> >         int err;
> > 
> > -       /* key consists of keys of equal size concatenated, therefore
> > -        * the length must be even
> > -        */
> > -       if (keylen % 2) {
> > -               *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > -               return -EINVAL;
> > -       }
> > +       err = xts_check_key(tfm, key, keylen);
> > +       if (err)
> > +               return err;
> > 
> >         /* first half of xts-key is for crypt */
> >         err = aes_set_key_common(tfm, ctx->raw_crypt_ctx, key, keylen /
> >         2);
> > 
> > diff --git a/arch/x86/crypto/camellia_glue.c
> > b/arch/x86/crypto/camellia_glue.c index 5c8b626..aa76cad 100644
> > --- a/arch/x86/crypto/camellia_glue.c
> > +++ b/arch/x86/crypto/camellia_glue.c
> > @@ -1503,13 +1503,9 @@ int xts_camellia_setkey(struct crypto_tfm *tfm,
> > const u8 *key,> 
> >         u32 *flags = &tfm->crt_flags;
> >         int err;
> > 
> > -       /* key consists of keys of equal size concatenated, therefore
> > -        * the length must be even
> > -        */
> > -       if (keylen % 2) {
> > -               *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > -               return -EINVAL;
> > -       }
> > +       err = xts_check_key(tfm, key, keylen);
> > +       if (err)
> > +               return err;
> > 
> >         /* first half of xts-key is for crypt */
> >         err = __camellia_setkey(&ctx->crypt_ctx, key, keylen / 2, flags);
> > 
> > diff --git a/arch/x86/crypto/cast6_avx_glue.c
> > b/arch/x86/crypto/cast6_avx_glue.c index fca4595..50e6847 100644
> > --- a/arch/x86/crypto/cast6_avx_glue.c
> > +++ b/arch/x86/crypto/cast6_avx_glue.c
> > @@ -329,13 +329,9 @@ static int xts_cast6_setkey(struct crypto_tfm *tfm,
> > const u8 *key,> 
> >         u32 *flags = &tfm->crt_flags;
> >         int err;
> > 
> > -       /* key consists of keys of equal size concatenated, therefore
> > -        * the length must be even
> > -        */
> > -       if (keylen % 2) {
> > -               *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > -               return -EINVAL;
> > -       }
> > +       err = xts_check_key(tfm, key, keylen);
> > +       if (err)
> > +               return err;
> > 
> >         /* first half of xts-key is for crypt */
> >         err = __cast6_setkey(&ctx->crypt_ctx, key, keylen / 2, flags);
> > 
> > diff --git a/arch/x86/crypto/serpent_avx_glue.c
> > b/arch/x86/crypto/serpent_avx_glue.c index 5dc3702..6f778d3 100644
> > --- a/arch/x86/crypto/serpent_avx_glue.c
> > +++ b/arch/x86/crypto/serpent_avx_glue.c
> > @@ -332,16 +332,11 @@ int xts_serpent_setkey(struct crypto_tfm *tfm, const
> > u8 *key,> 
> >                        unsigned int keylen)
> >  
> >  {
> >  
> >         struct serpent_xts_ctx *ctx = crypto_tfm_ctx(tfm);
> > 
> > -       u32 *flags = &tfm->crt_flags;
> > 
> >         int err;
> > 
> > -       /* key consists of keys of equal size concatenated, therefore
> > -        * the length must be even
> > -        */
> > -       if (keylen % 2) {
> > -               *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > -               return -EINVAL;
> > -       }
> > +       err = xts_check_key(tfm, key, keylen);
> > +       if (err)
> > +               return err;
> > 
> >         /* first half of xts-key is for crypt */
> >         err = __serpent_setkey(&ctx->crypt_ctx, key, keylen / 2);
> > 
> > diff --git a/arch/x86/crypto/serpent_sse2_glue.c
> > b/arch/x86/crypto/serpent_sse2_glue.c index 3643dd5..8943407 100644
> > --- a/arch/x86/crypto/serpent_sse2_glue.c
> > +++ b/arch/x86/crypto/serpent_sse2_glue.c
> > @@ -309,16 +309,11 @@ static int xts_serpent_setkey(struct crypto_tfm
> > *tfm, const u8 *key,> 
> >                               unsigned int keylen)
> >  
> >  {
> >  
> >         struct serpent_xts_ctx *ctx = crypto_tfm_ctx(tfm);
> > 
> > -       u32 *flags = &tfm->crt_flags;
> > 
> >         int err;
> > 
> > -       /* key consists of keys of equal size concatenated, therefore
> > -        * the length must be even
> > -        */
> > -       if (keylen % 2) {
> > -               *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > -               return -EINVAL;
> > -       }
> > +       err = xts_check_key(tfm, key, keylen);
> > +       if (err)
> > +               return err;
> > 
> >         /* first half of xts-key is for crypt */
> >         err = __serpent_setkey(&ctx->crypt_ctx, key, keylen / 2);
> > 
> > diff --git a/arch/x86/crypto/twofish_glue_3way.c
> > b/arch/x86/crypto/twofish_glue_3way.c index 56d8a08..2ebb5e9 100644
> > --- a/arch/x86/crypto/twofish_glue_3way.c
> > +++ b/arch/x86/crypto/twofish_glue_3way.c
> > @@ -277,13 +277,9 @@ int xts_twofish_setkey(struct crypto_tfm *tfm, const
> > u8 *key,> 
> >         u32 *flags = &tfm->crt_flags;
> >         int err;
> > 
> > -       /* key consists of keys of equal size concatenated, therefore
> > -        * the length must be even
> > -        */
> > -       if (keylen % 2) {
> > -               *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > -               return -EINVAL;
> > -       }
> > +       err = xts_check_key(tfm, key, keylen);
> > +       if (err)
> > +               return err;
> > 
> >         /* first half of xts-key is for crypt */
> >         err = __twofish_setkey(&ctx->crypt_ctx, key, keylen / 2, flags);
> > 
> > diff --git a/crypto/xts.c b/crypto/xts.c
> > index f6fd43f..26ba583 100644
> > --- a/crypto/xts.c
> > +++ b/crypto/xts.c
> > @@ -35,16 +35,11 @@ static int setkey(struct crypto_tfm *parent, const u8
> > *key,> 
> >  {
> >  
> >         struct priv *ctx = crypto_tfm_ctx(parent);
> >         struct crypto_cipher *child = ctx->tweak;
> > 
> > -       u32 *flags = &parent->crt_flags;
> > 
> >         int err;
> > 
> > -       /* key consists of keys of equal size concatenated, therefore
> > -        * the length must be even */
> > -       if (keylen % 2) {
> > -               /* tell the user why there was an error */
> > -               *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > -               return -EINVAL;
> > -       }
> > +       err = xts_check_key(parent, key, keylen);
> > +       if (err)
> > +               return err;
> > 
> >         /* we need two cipher instances: one to compute the initial
> >         'tweak'
> >         
> >          * by encrypting the IV (usually the 'plain' iv) and the other
> > 
> > diff --git a/include/crypto/xts.h b/include/crypto/xts.h
> > index 72c09eb..41d936e 100644
> > --- a/include/crypto/xts.h
> > +++ b/include/crypto/xts.h
> > @@ -2,6 +2,9 @@
> > 
> >  #define _CRYPTO_XTS_H
> >  
> >  #include <crypto/b128ops.h>
> > 
> > +#include <linux/crypto.h>
> > +#include <crypto/algapi.h>
> > +#include <linux/fips.h>
> > 
> >  struct scatterlist;
> >  struct blkcipher_desc;
> > 
> > @@ -24,4 +27,30 @@ int xts_crypt(struct blkcipher_desc *desc, struct
> > scatterlist *dst,> 
> >               struct scatterlist *src, unsigned int nbytes,
> >               struct xts_crypt_req *req);
> > 
> > +static inline int xts_check_key(struct crypto_tfm *tfm,
> > +                               const u8 *key, unsigned int keylen)
> > +{
> > +       u32 *flags = &tfm->crt_flags;
> > +
> > +       /*
> > +        * key consists of keys of equal size concatenated, therefore
> > +        * the length must be even.
> > +        */
> > +       if (keylen % 2) {
> > +               /* tell the user why there was an error */
> 
> Nit: I don't think this comment adds anything useful tbh

I just copied it from the x86 code -- I will remove it.
> 
> > +               *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
> > +               return -EINVAL;
> > +       }
> > +
> > +#ifdef CONFIG_CRYPTO_FIPS
> > +       /* ensure that the AES and tweak key are not identical */
> > +       if (fips_enabled &&
> 
> This is redundant. 'fips_enabled' is #defined to 0 if CRYPTO_FIPS=n so
> you can lose the #ifdef entirely.

I would concur. But then we have an additional check which is not really 
required in the "normal" use case.

As I have seen that all FIPS related stuff is encapsulated with the FIPS 
ifdef, I thought this is warranted here too.

I am fine either way though.

Herbert, what do you think?
> 
> > +           !crypto_memneq(key, key + (keylen / 2), keylen / 2)) {
> > +               *flags |= CRYPTO_TFM_RES_WEAK_KEY;
> > +               return -EINVAL;
> > +       }
> > +#endif
> > +       return 0;
> > +}
> > +
> > 
> >  #endif  /* _CRYPTO_XTS_H */
> > 
> > --
> > 2.5.0


Ciao
Stephan