On Thu, Aug 09, 2018 at 12:07:18PM -0700, Eric Biggers wrote:
> On Thu, Aug 09, 2018 at 08:38:56PM +0200, Stephan Müller wrote:
> > The function extract_crng invokes the ChaCha20 block operation directly
> > on the user-provided buffer. The block operation operates on u32 words.
> > Thus the extract_crng function expects the buffer to be aligned to u32
> > as it is visible with the parameter type of extract_crng. However,
> > get_random_bytes uses a void pointer which may or may not be aligned.
> > Thus, an alignment check is necessary and the temporary buffer must be
> > used if the alignment to u32 is not ensured.
> >
> > Cc: <sta...@vger.kernel.org> # v4.16+
> > Cc: Ted Tso <ty...@mit.edu>
> > Signed-off-by: Stephan Mueller <smuel...@chronox.de>
> > ---
> > drivers/char/random.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/char/random.c b/drivers/char/random.c
> > index bd449ad52442..23f336872426 100644
> > --- a/drivers/char/random.c
> > +++ b/drivers/char/random.c
> > @@ -1617,8 +1617,14 @@ static void _get_random_bytes(void *buf, int nbytes)
> > trace_get_random_bytes(nbytes, _RET_IP_);
> >
> > while (nbytes >= CHACHA20_BLOCK_SIZE) {
> > - extract_crng(buf);
> > - buf += CHACHA20_BLOCK_SIZE;
> > + if (likely((unsigned long)buf & (sizeof(tmp[0]) - 1))) {
> > + extract_crng(buf);
> > + buf += CHACHA20_BLOCK_SIZE;
> > + } else {
> > + extract_crng(tmp);
> > + memcpy(buf, tmp, CHACHA20_BLOCK_SIZE);
> > + }
> > +
> > nbytes -= CHACHA20_BLOCK_SIZE;
> > }
> >
> > --
> > 2.17.1
>
> This patch is backwards: the temporary buffer is used when the buffer is
> *aligned*, not misaligned. And more problematically, 'buf' is never
> incremented
> in one of the cases...
>
> Note that I had tried to fix the chacha20_block() alignment bugs in commit
> 9f480faec58cd6197a ("crypto: chacha20 - Fix keystream alignment for
> chacha20_block()"), but I had missed this case. I don't like seeing the
> alignment requirement being worked around with a temporary buffer; it's
> error-prone, and inefficient on common platforms. How about we instead make
> the
> output of chacha20_block() a u8 array and output the 16 32-bit words using
> put_unaligned_le32()? In retrospect I probably should have just done that,
> but
> at the time I didn't know of any case where the alignment would be a problem.
>
> - Eric
For example:
-----8<-----
From: Eric Biggers <ebigg...@google.com>
Subject: [PATCH] crypto: chacha20 - Fix keystream alignment for
chacha20_block() (again)
In commit 9f480faec58cd6 ("crypto: chacha20 - Fix keystream alignment
for chacha20_block()") I had missed that chacha20_block() can end up
being called on the buffer passed to get_random_bytes(), which can have
any alignment. So, while my commit didn't break anything since
chacha20_block() has actually always had a u32-alignment requirement for
the output, 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 doesn't have to be aligned.
This is simpler, and on many CPUs it's the same speed.
Reported-by: Stephan Müller <smuel...@chronox.de>
Signed-off-by: Eric Biggers <ebigg...@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 bd449ad52442..b8f4345a50f4 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);
@@ -912,7 +912,7 @@ 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;
@@ -959,7 +959,7 @@ 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;
@@ -976,7 +976,7 @@ 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;
@@ -994,7 +994,7 @@ 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;
@@ -1006,14 +1006,14 @@ 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;
@@ -1029,7 +1029,7 @@ 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];
int large_request = (nbytes > 256);
while (nbytes) {
@@ -1612,7 +1612,7 @@ 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];
trace_get_random_bytes(nbytes, _RET_IP_);
@@ -2222,7 +2222,7 @@ 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++];
@@ -2252,7 +2252,7 @@ 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]++;
}
--
2.18.0.597.ga71716f1ad-goog
