diff mbox series

crypto: chacha20 - Fix chacha20_block() keystream alignment (again)

Message ID 20180912030510.27025-1-ebiggers@kernel.org (mailing list archive)
State Accepted
Delegated to: Herbert Xu
Headers show
Series crypto: chacha20 - Fix chacha20_block() keystream alignment (again) | expand

Commit Message

Eric Biggers Sept. 12, 2018, 3:05 a.m. UTC 
From: Eric Biggers <ebiggers@google.com>

In commit 9f480faec58c ("crypto: chacha20 - Fix keystream alignment for
chacha20_block()"), I had missed that chacha20_block() can be called
directly on the buffer passed to get_random_bytes(), which can have any
alignment.  So, while my commit didn't break anything, it didn't fully
solve the alignment problems.

Revert my solution and just update chacha20_block() to use
put_unaligned_le32(), so the output buffer need not be aligned.
This is simpler, and on many CPUs it's the same speed.

But, I kept the 'tmp' buffers in extract_crng_user() and
_get_random_bytes() 4-byte aligned, since that alignment is actually
needed for _crng_backtrack_protect() too.

Reported-by: Stephan Müller <smueller@chronox.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/chacha20_generic.c |  7 ++++---
 drivers/char/random.c     | 24 ++++++++++++------------
 include/crypto/chacha20.h |  3 +--
 lib/chacha20.c            |  6 +++---
 4 files changed, 20 insertions(+), 20 deletions(-)

Comments

Yann Droneaud Sept. 12, 2018, 9:50 a.m. UTC | #1 
Hi,

Le mardi 11 septembre 2018 à 20:05 -0700, Eric Biggers a écrit :
> From: Eric Biggers <ebiggers@google.com>
> 
> In commit 9f480faec58c ("crypto: chacha20 - Fix keystream alignment for
> chacha20_block()"), I had missed that chacha20_block() can be called
> directly on the buffer passed to get_random_bytes(), which can have any
> alignment.  So, while my commit didn't break anything, it didn't fully
> solve the alignment problems.
> 
> Revert my solution and just update chacha20_block() to use
> put_unaligned_le32(), so the output buffer need not be aligned.
> This is simpler, and on many CPUs it's the same speed.
> 
> But, I kept the 'tmp' buffers in extract_crng_user() and
> _get_random_bytes() 4-byte aligned, since that alignment is actually
> needed for _crng_backtrack_protect() too.
> 
> Reported-by: Stephan Müller <smueller@chronox.de>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  crypto/chacha20_generic.c |  7 ++++---
>  drivers/char/random.c     | 24 ++++++++++++------------
>  include/crypto/chacha20.h |  3 +--
>  lib/chacha20.c            |  6 +++---
>  4 files changed, 20 insertions(+), 20 deletions(-)
> 
> diff --git a/crypto/chacha20_generic.c b/crypto/chacha20_generic.c
> index e451c3cb6a56..3ae96587caf9 100644
> --- a/crypto/chacha20_generic.c
> +++ b/crypto/chacha20_generic.c
> @@ -18,20 +18,21 @@
>  static void chacha20_docrypt(u32 *state, u8 *dst, const u8 *src,
>  			     unsigned int bytes)
>  {
> -	u32 stream[CHACHA20_BLOCK_WORDS];
> +	/* aligned to potentially speed up crypto_xor() */
> +	u8 stream[CHACHA20_BLOCK_SIZE] __aligned(sizeof(long));
>  
>  	if (dst != src)
>  		memcpy(dst, src, bytes);
>  
>  	while (bytes >= CHACHA20_BLOCK_SIZE) {
>  		chacha20_block(state, stream);
> -		crypto_xor(dst, (const u8 *)stream, CHACHA20_BLOCK_SIZE);
> +		crypto_xor(dst, stream, CHACHA20_BLOCK_SIZE);
>  		bytes -= CHACHA20_BLOCK_SIZE;
>  		dst += CHACHA20_BLOCK_SIZE;
>  	}
>  	if (bytes) {
>  		chacha20_block(state, stream);
> -		crypto_xor(dst, (const u8 *)stream, bytes);
> +		crypto_xor(dst, stream, bytes);
>  	}
>  }
>  
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index bf5f99fc36f1..d22d967c50f0 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1003,7 +1003,7 @@ static void extract_crng(__u32 out[CHACHA20_BLOCK_WORDS])
>   * enough) to mutate the CRNG key to provide backtracking protection.
>   */
>  static void _crng_backtrack_protect(struct crng_state *crng,
> -				    __u32 tmp[CHACHA20_BLOCK_WORDS], int used)
> +				    __u8 tmp[CHACHA20_BLOCK_SIZE], int used)
>  {
>  	unsigned long	flags;
>  	__u32		*s, *d;
> @@ -1015,14 +1015,14 @@ static void _crng_backtrack_protect(struct crng_state *crng,
>  		used = 0;
>  	}
>  	spin_lock_irqsave(&crng->lock, flags);
> -	s = &tmp[used / sizeof(__u32)];
> +	s = (__u32 *) &tmp[used];

This introduces a alignment issue: tmp is not aligned for __u32, but is
dereferenced as such later.

>  	d = &crng->state[4];
>  	for (i=0; i < 8; i++)
>  		*d++ ^= *s++;
>  	spin_unlock_irqrestore(&crng->lock, flags);
>  }
>  

Regards.
Eric Biggers Sept. 14, 2018, 4:25 p.m. UTC | #2 
Hi Yann,

On Wed, Sep 12, 2018 at 11:50:00AM +0200, Yann Droneaud wrote:
> Hi,
> 
> Le mardi 11 septembre 2018 à 20:05 -0700, Eric Biggers a écrit :
> > From: Eric Biggers <ebiggers@google.com>
> > 
> > In commit 9f480faec58c ("crypto: chacha20 - Fix keystream alignment for
> > chacha20_block()"), I had missed that chacha20_block() can be called
> > directly on the buffer passed to get_random_bytes(), which can have any
> > alignment.  So, while my commit didn't break anything, it didn't fully
> > solve the alignment problems.
> > 
> > Revert my solution and just update chacha20_block() to use
> > put_unaligned_le32(), so the output buffer need not be aligned.
> > This is simpler, and on many CPUs it's the same speed.
> > 
> > But, I kept the 'tmp' buffers in extract_crng_user() and
> > _get_random_bytes() 4-byte aligned, since that alignment is actually
> > needed for _crng_backtrack_protect() too.
> > 
> > Reported-by: Stephan Müller <smueller@chronox.de>
> > Cc: Theodore Ts'o <tytso@mit.edu>
> > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > ---
> >  crypto/chacha20_generic.c |  7 ++++---
> >  drivers/char/random.c     | 24 ++++++++++++------------
> >  include/crypto/chacha20.h |  3 +--
> >  lib/chacha20.c            |  6 +++---
> >  4 files changed, 20 insertions(+), 20 deletions(-)
> > 
> > diff --git a/crypto/chacha20_generic.c b/crypto/chacha20_generic.c
> > index e451c3cb6a56..3ae96587caf9 100644
> > --- a/crypto/chacha20_generic.c
> > +++ b/crypto/chacha20_generic.c
> > @@ -18,20 +18,21 @@
> >  static void chacha20_docrypt(u32 *state, u8 *dst, const u8 *src,
> >  			     unsigned int bytes)
> >  {
> > -	u32 stream[CHACHA20_BLOCK_WORDS];
> > +	/* aligned to potentially speed up crypto_xor() */
> > +	u8 stream[CHACHA20_BLOCK_SIZE] __aligned(sizeof(long));
> >  
> >  	if (dst != src)
> >  		memcpy(dst, src, bytes);
> >  
> >  	while (bytes >= CHACHA20_BLOCK_SIZE) {
> >  		chacha20_block(state, stream);
> > -		crypto_xor(dst, (const u8 *)stream, CHACHA20_BLOCK_SIZE);
> > +		crypto_xor(dst, stream, CHACHA20_BLOCK_SIZE);
> >  		bytes -= CHACHA20_BLOCK_SIZE;
> >  		dst += CHACHA20_BLOCK_SIZE;
> >  	}
> >  	if (bytes) {
> >  		chacha20_block(state, stream);
> > -		crypto_xor(dst, (const u8 *)stream, bytes);
> > +		crypto_xor(dst, stream, bytes);
> >  	}
> >  }
> >  
> > diff --git a/drivers/char/random.c b/drivers/char/random.c
> > index bf5f99fc36f1..d22d967c50f0 100644
> > --- a/drivers/char/random.c
> > +++ b/drivers/char/random.c
> > @@ -1003,7 +1003,7 @@ static void extract_crng(__u32 out[CHACHA20_BLOCK_WORDS])
> >   * enough) to mutate the CRNG key to provide backtracking protection.
> >   */
> >  static void _crng_backtrack_protect(struct crng_state *crng,
> > -				    __u32 tmp[CHACHA20_BLOCK_WORDS], int used)
> > +				    __u8 tmp[CHACHA20_BLOCK_SIZE], int used)
> >  {
> >  	unsigned long	flags;
> >  	__u32		*s, *d;
> > @@ -1015,14 +1015,14 @@ static void _crng_backtrack_protect(struct crng_state *crng,
> >  		used = 0;
> >  	}
> >  	spin_lock_irqsave(&crng->lock, flags);
> > -	s = &tmp[used / sizeof(__u32)];
> > +	s = (__u32 *) &tmp[used];
> 
> This introduces a alignment issue: tmp is not aligned for __u32, but is
> dereferenced as such later.
> 
> >  	d = &crng->state[4];
> >  	for (i=0; i < 8; i++)
> >  		*d++ ^= *s++;
> >  	spin_unlock_irqrestore(&crng->lock, flags);
> >  }
> >  
> 

I explained this in the patch; the callers ensure the buffer is aligned.

- Eric
Herbert Xu Sept. 21, 2018, 5:44 a.m. UTC | #3 
On Tue, Sep 11, 2018 at 08:05:10PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> In commit 9f480faec58c ("crypto: chacha20 - Fix keystream alignment for
> chacha20_block()"), I had missed that chacha20_block() can be called
> directly on the buffer passed to get_random_bytes(), which can have any
> alignment.  So, while my commit didn't break anything, it didn't fully
> solve the alignment problems.
> 
> Revert my solution and just update chacha20_block() to use
> put_unaligned_le32(), so the output buffer need not be aligned.
> This is simpler, and on many CPUs it's the same speed.
> 
> But, I kept the 'tmp' buffers in extract_crng_user() and
> _get_random_bytes() 4-byte aligned, since that alignment is actually
> needed for _crng_backtrack_protect() too.
> 
> Reported-by: Stephan Müller <smueller@chronox.de>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  crypto/chacha20_generic.c |  7 ++++---
>  drivers/char/random.c     | 24 ++++++++++++------------
>  include/crypto/chacha20.h |  3 +--
>  lib/chacha20.c            |  6 +++---
>  4 files changed, 20 insertions(+), 20 deletions(-)

Patch applied.  Thanks.
diff mbox series

Patch

diff --git a/crypto/chacha20_generic.c b/crypto/chacha20_generic.c
index e451c3cb6a56..3ae96587caf9 100644
--- a/crypto/chacha20_generic.c
+++ b/crypto/chacha20_generic.c
@@ -18,20 +18,21 @@ 
 static void chacha20_docrypt(u32 *state, u8 *dst, const u8 *src,
 			     unsigned int bytes)
 {
-	u32 stream[CHACHA20_BLOCK_WORDS];
+	/* aligned to potentially speed up crypto_xor() */
+	u8 stream[CHACHA20_BLOCK_SIZE] __aligned(sizeof(long));
 
 	if (dst != src)
 		memcpy(dst, src, bytes);
 
 	while (bytes >= CHACHA20_BLOCK_SIZE) {
 		chacha20_block(state, stream);
-		crypto_xor(dst, (const u8 *)stream, CHACHA20_BLOCK_SIZE);
+		crypto_xor(dst, stream, CHACHA20_BLOCK_SIZE);
 		bytes -= CHACHA20_BLOCK_SIZE;
 		dst += CHACHA20_BLOCK_SIZE;
 	}
 	if (bytes) {
 		chacha20_block(state, stream);
-		crypto_xor(dst, (const u8 *)stream, bytes);
+		crypto_xor(dst, stream, bytes);
 	}
 }
 
diff --git a/drivers/char/random.c b/drivers/char/random.c
index bf5f99fc36f1..d22d967c50f0 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -433,9 +433,9 @@  static int crng_init_cnt = 0;
 static unsigned long crng_global_init_time = 0;
 #define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)
 static void _extract_crng(struct crng_state *crng,
-			  __u32 out[CHACHA20_BLOCK_WORDS]);
+			  __u8 out[CHACHA20_BLOCK_SIZE]);
 static void _crng_backtrack_protect(struct crng_state *crng,
-				    __u32 tmp[CHACHA20_BLOCK_WORDS], int used);
+				    __u8 tmp[CHACHA20_BLOCK_SIZE], int used);
 static void process_random_ready_list(void);
 static void _get_random_bytes(void *buf, int nbytes);
 
@@ -921,7 +921,7 @@  static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
 	unsigned long	flags;
 	int		i, num;
 	union {
-		__u32	block[CHACHA20_BLOCK_WORDS];
+		__u8	block[CHACHA20_BLOCK_SIZE];
 		__u32	key[8];
 	} buf;
 
@@ -968,7 +968,7 @@  static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
 }
 
 static void _extract_crng(struct crng_state *crng,
-			  __u32 out[CHACHA20_BLOCK_WORDS])
+			  __u8 out[CHACHA20_BLOCK_SIZE])
 {
 	unsigned long v, flags;
 
@@ -985,7 +985,7 @@  static void _extract_crng(struct crng_state *crng,
 	spin_unlock_irqrestore(&crng->lock, flags);
 }
 
-static void extract_crng(__u32 out[CHACHA20_BLOCK_WORDS])
+static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
 {
 	struct crng_state *crng = NULL;
 
@@ -1003,7 +1003,7 @@  static void extract_crng(__u32 out[CHACHA20_BLOCK_WORDS])
  * enough) to mutate the CRNG key to provide backtracking protection.
  */
 static void _crng_backtrack_protect(struct crng_state *crng,
-				    __u32 tmp[CHACHA20_BLOCK_WORDS], int used)
+				    __u8 tmp[CHACHA20_BLOCK_SIZE], int used)
 {
 	unsigned long	flags;
 	__u32		*s, *d;
@@ -1015,14 +1015,14 @@  static void _crng_backtrack_protect(struct crng_state *crng,
 		used = 0;
 	}
 	spin_lock_irqsave(&crng->lock, flags);
-	s = &tmp[used / sizeof(__u32)];
+	s = (__u32 *) &tmp[used];
 	d = &crng->state[4];
 	for (i=0; i < 8; i++)
 		*d++ ^= *s++;
 	spin_unlock_irqrestore(&crng->lock, flags);
 }
 
-static void crng_backtrack_protect(__u32 tmp[CHACHA20_BLOCK_WORDS], int used)
+static void crng_backtrack_protect(__u8 tmp[CHACHA20_BLOCK_SIZE], int used)
 {
 	struct crng_state *crng = NULL;
 
@@ -1038,7 +1038,7 @@  static void crng_backtrack_protect(__u32 tmp[CHACHA20_BLOCK_WORDS], int used)
 static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
 {
 	ssize_t ret = 0, i = CHACHA20_BLOCK_SIZE;
-	__u32 tmp[CHACHA20_BLOCK_WORDS];
+	__u8 tmp[CHACHA20_BLOCK_SIZE] __aligned(4);
 	int large_request = (nbytes > 256);
 
 	while (nbytes) {
@@ -1617,7 +1617,7 @@  static void _warn_unseeded_randomness(const char *func_name, void *caller,
  */
 static void _get_random_bytes(void *buf, int nbytes)
 {
-	__u32 tmp[CHACHA20_BLOCK_WORDS];
+	__u8 tmp[CHACHA20_BLOCK_SIZE] __aligned(4);
 
 	trace_get_random_bytes(nbytes, _RET_IP_);
 
@@ -2243,7 +2243,7 @@  u64 get_random_u64(void)
 	if (use_lock)
 		read_lock_irqsave(&batched_entropy_reset_lock, flags);
 	if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
-		extract_crng((__u32 *)batch->entropy_u64);
+		extract_crng((u8 *)batch->entropy_u64);
 		batch->position = 0;
 	}
 	ret = batch->entropy_u64[batch->position++];
@@ -2273,7 +2273,7 @@  u32 get_random_u32(void)
 	if (use_lock)
 		read_lock_irqsave(&batched_entropy_reset_lock, flags);
 	if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
-		extract_crng(batch->entropy_u32);
+		extract_crng((u8 *)batch->entropy_u32);
 		batch->position = 0;
 	}
 	ret = batch->entropy_u32[batch->position++];
diff --git a/include/crypto/chacha20.h b/include/crypto/chacha20.h
index b83d66073db0..f76302d99e2b 100644
--- a/include/crypto/chacha20.h
+++ b/include/crypto/chacha20.h
@@ -13,13 +13,12 @@ 
 #define CHACHA20_IV_SIZE	16
 #define CHACHA20_KEY_SIZE	32
 #define CHACHA20_BLOCK_SIZE	64
-#define CHACHA20_BLOCK_WORDS	(CHACHA20_BLOCK_SIZE / sizeof(u32))
 
 struct chacha20_ctx {
 	u32 key[8];
 };
 
-void chacha20_block(u32 *state, u32 *stream);
+void chacha20_block(u32 *state, u8 *stream);
 void crypto_chacha20_init(u32 *state, struct chacha20_ctx *ctx, u8 *iv);
 int crypto_chacha20_setkey(struct crypto_skcipher *tfm, const u8 *key,
 			   unsigned int keysize);
diff --git a/lib/chacha20.c b/lib/chacha20.c
index c1cc50fb68c9..d907fec6a9ed 100644
--- a/lib/chacha20.c
+++ b/lib/chacha20.c
@@ -16,9 +16,9 @@ 
 #include <asm/unaligned.h>
 #include <crypto/chacha20.h>
 
-void chacha20_block(u32 *state, u32 *stream)
+void chacha20_block(u32 *state, u8 *stream)
 {
-	u32 x[16], *out = stream;
+	u32 x[16];
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(x); i++)
@@ -67,7 +67,7 @@  void chacha20_block(u32 *state, u32 *stream)
 	}
 
 	for (i = 0; i < ARRAY_SIZE(x); i++)
-		out[i] = cpu_to_le32(x[i] + state[i]);
+		put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]);
 
 	state[12]++;
 }