[PATCH] crypto: cmac - fix alignment of 'consts'

[PATCH] crypto: cmac - fix alignment of 'consts'

[Eric Biggers]

The per-transform 'consts' array is accessed as __be64 in
crypto_cmac_digest_setkey() but was only guaranteed to be aligned to
__alignof__(long).  Fix this by aligning it to __alignof__(__be64).

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/cmac.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/crypto/cmac.c b/crypto/cmac.c
index b6c4059..04080dc 100644
--- a/crypto/cmac.c
+++ b/crypto/cmac.c
@@ -57,7 +57,8 @@ static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
 	unsigned long alignmask = crypto_shash_alignmask(parent);
 	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
 	unsigned int bs = crypto_shash_blocksize(parent);
-	__be64 *consts = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
+	__be64 *consts = PTR_ALIGN((void *)ctx->ctx,
+				   (alignmask | (__alignof__(__be64) - 1)) + 1);
 	u64 _const[2];
 	int i, err = 0;
 	u8 msb_mask, gfmask;
@@ -173,7 +174,8 @@ static int crypto_cmac_digest_final(struct shash_desc *pdesc, u8 *out)
 	struct cmac_desc_ctx *ctx = shash_desc_ctx(pdesc);
 	struct crypto_cipher *tfm = tctx->child;
 	int bs = crypto_shash_blocksize(parent);
-	u8 *consts = PTR_ALIGN((void *)tctx->ctx, alignmask + 1);
+	u8 *consts = PTR_ALIGN((void *)tctx->ctx,
+			       (alignmask | (__alignof__(__be64) - 1)) + 1);
 	u8 *odds = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
 	u8 *prev = odds + bs;
 	unsigned int offset = 0;
@@ -258,7 +260,8 @@ static int cmac_create(struct crypto_template *tmpl, struct rtattr **tb)
 	if (err)
 		goto out_free_inst;
 
-	alignmask = alg->cra_alignmask | (sizeof(long) - 1);
+	/* We access the data as u32s when xoring. */
+	alignmask = alg->cra_alignmask | (__alignof__(u32) - 1);
 	inst->alg.base.cra_alignmask = alignmask;
 	inst->alg.base.cra_priority = alg->cra_priority;
 	inst->alg.base.cra_blocksize = alg->cra_blocksize;
@@ -270,7 +273,9 @@ static int cmac_create(struct crypto_template *tmpl, struct rtattr **tb)
 		+ alg->cra_blocksize * 2;
 
 	inst->alg.base.cra_ctxsize =
-		ALIGN(sizeof(struct cmac_tfm_ctx), alignmask + 1)
+		ALIGN(sizeof(struct cmac_tfm_ctx), crypto_tfm_ctx_alignment())
+		+ ((alignmask | (__alignof__(__be64) - 1)) &
+		   ~(crypto_tfm_ctx_alignment() - 1))
 		+ alg->cra_blocksize * 2;
 
 	inst->alg.base.cra_init = cmac_init_tfm;
-- 
2.8.0.rc3.226.g39d4020

Re: [PATCH] crypto: cmac - fix alignment of 'consts'

[Joe Perches]

On Mon, 2016-10-10 at 10:15 -0700, Eric Biggers wrote:
> The per-transform 'consts' array is accessed as __be64 in
> crypto_cmac_digest_setkey() but was only guaranteed to be aligned to
> __alignof__(long).  Fix this by aligning it to __alignof__(__be64).
[]
> diff --git a/crypto/cmac.c b/crypto/cmac.c
[]
> @@ -57,7 +57,8 @@ static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
>  	unsigned long alignmask = crypto_shash_alignmask(parent);
>  	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
>  	unsigned int bs = crypto_shash_blocksize(parent);
> -	__be64 *consts = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
> +	__be64 *consts = PTR_ALIGN((void *)ctx->ctx,
> +				   (alignmask | (__alignof__(__be64) - 1)) + 1);

Using a bitwise or looks very odd there.  Perhaps:

		min(alignmask + 1, __alignof__(__be64))

Re: [PATCH] crypto: cmac - fix alignment of 'consts'

[Eric Biggers]

On Mon, Oct 10, 2016 at 10:29:55AM -0700, Joe Perches wrote:
> On Mon, 2016-10-10 at 10:15 -0700, Eric Biggers wrote:
> > The per-transform 'consts' array is accessed as __be64 in
> > crypto_cmac_digest_setkey() but was only guaranteed to be aligned to
> > __alignof__(long).  Fix this by aligning it to __alignof__(__be64).
> []
> > diff --git a/crypto/cmac.c b/crypto/cmac.c
> []
> > @@ -57,7 +57,8 @@ static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
> >  	unsigned long alignmask = crypto_shash_alignmask(parent);
> >  	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
> >  	unsigned int bs = crypto_shash_blocksize(parent);
> > -	__be64 *consts = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
> > +	__be64 *consts = PTR_ALIGN((void *)ctx->ctx,
> > +				   (alignmask | (__alignof__(__be64) - 1)) + 1);
> 
> Using a bitwise or looks very odd there.  Perhaps:
> 
> 		min(alignmask + 1, __alignof__(__be64))
> 

Alignment has to be a power of 2.  From the code I've read, crypto drivers work
with alignment a lot and use bitwise OR to mean "the more restrictive of these
alignmasks".  So I believe the way it's written is the preferred style.

Eric

Re: [PATCH] crypto: cmac - fix alignment of 'consts'

[Joe Perches]

On Mon, 2016-10-10 at 10:37 -0700, Eric Biggers wrote:
> On Mon, Oct 10, 2016 at 10:29:55AM -0700, Joe Perches wrote:
> > On Mon, 2016-10-10 at 10:15 -0700, Eric Biggers wrote:
> > > The per-transform 'consts' array is accessed as __be64 in
> > > crypto_cmac_digest_setkey() but was only guaranteed to be aligned to
> > > __alignof__(long).  Fix this by aligning it to __alignof__(__be64).
> > []
> > > diff --git a/crypto/cmac.c b/crypto/cmac.c
> > []
> > > @@ -57,7 +57,8 @@ static int crypto_cmac_digest_setkey(struct crypto_shash *parent,
> > >  	unsigned long alignmask = crypto_shash_alignmask(parent);
> > >  	struct cmac_tfm_ctx *ctx = crypto_shash_ctx(parent);
> > >  	unsigned int bs = crypto_shash_blocksize(parent);
> > > -	__be64 *consts = PTR_ALIGN((void *)ctx->ctx, alignmask + 1);
> > > +	__be64 *consts = PTR_ALIGN((void *)ctx->ctx,
> > > +				   (alignmask | (__alignof__(__be64) - 1)) + 1);
> > 
> > 
> > Using a bitwise or looks very odd there.  Perhaps:
> > 
> > 		min(alignmask + 1, __alignof__(__be64))
> > 
> 
> 
> Alignment has to be a power of 2.  From the code I've read, crypto drivers work
> with alignment a lot and use bitwise OR to mean "the more restrictive of these
> alignmasks".  So I believe the way it's written is the preferred style.
> 
> Eric

Hey Eric.

I don't see any PTR_ALIGN uses in crypto/ or drivers/crypto/ that
use a bitwise or, just mask + 1, but I believe the effect is the
same.  Anyway, your choice, but I think using min is clearer.

cheers, Joe

Re: [PATCH] crypto: cmac - fix alignment of 'consts'

[Eric Biggers]

On Mon, Oct 10, 2016 at 10:51:14AM -0700, Joe Perches wrote:
> 
> Hey Eric.
> 
> I don't see any PTR_ALIGN uses in crypto/ or drivers/crypto/ that
> use a bitwise or, just mask + 1, but I believe the effect is the
> same.  Anyway, your choice, but I think using min is clearer.
> 
> cheers, Joe

Usually the bitwise OR is used when setting cra_alignmask in the 'struct
crypto_alg'.  Indeed, the problem could be solved by setting

	inst->alg.base.cra_alignmask = alg->cra_alignmask | (__alignof__(__be64) - 1);

I decided against that because it would always force 8-byte alignment for CMAC
input buffers and keys, when in fact they don't need that level of alignment
unless the underlying block cipher requires it.

Eric

Re: [PATCH] crypto: cmac - fix alignment of 'consts'

[Herbert Xu]

On Mon, Oct 10, 2016 at 10:15:15AM -0700, Eric Biggers wrote:
> The per-transform 'consts' array is accessed as __be64 in
> crypto_cmac_digest_setkey() but was only guaranteed to be aligned to
> __alignof__(long).  Fix this by aligning it to __alignof__(__be64).
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt