Commit a5e9f557 authored by Eric Biggers's avatar Eric Biggers Committed by Herbert Xu
Browse files

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



In commit 9f480fae ("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: default avatarStephan Müller <smueller@chronox.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 78105c7e

crypto/chacha20_generic.c

+4 −3
Original line number Diff line number Diff line
@@ -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);

	}

}

drivers/char/random.c

+12 −12
Original line number Diff line number Diff line
@@ -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++];

include/crypto/chacha20.h

+1 −2
Original line number Diff line number Diff line
@@ -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);

lib/chacha20.c

+3 −3
Original line number Diff line number Diff line
@@ -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]++;

}

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