From: "Theodore Ts'o" <tytso@mit.edu>
To: Linux Kernel Developers List <linux-kernel@vger.kernel.org>
Cc: linux-crypto@vger.kernel.org, smueller@chronox.de,
herbert@gondor.apana.org.au, andi@firstfloor.org,
sandyinchina@gmail.com, jsd@av8n.com, hpa@zytor.com,
"Theodore Ts'o" <tytso@mit.edu>
Subject: [PATCH 7/7] random: add backtracking protection to the CRNG
Date: Mon, 13 Jun 2016 11:48:39 -0400 [thread overview]
Message-ID: <1465832919-11316-8-git-send-email-tytso@mit.edu> (raw)
In-Reply-To: <1465832919-11316-1-git-send-email-tytso@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
drivers/char/random.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 49 insertions(+), 5 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index d640865..963a6a9 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -436,7 +436,8 @@ static int crng_init = 0;
#define crng_ready() (likely(crng_init > 0))
static void _extract_crng(struct crng_state *crng,
__u8 out[CHACHA20_BLOCK_SIZE]);
-static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE]);
+static void _crng_backtrack_protect(struct crng_state *crng,
+ __u8 tmp[CHACHA20_BLOCK_SIZE], int used);
static void process_random_ready_list(void);
/**********************************************************************
@@ -826,8 +827,11 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
num = extract_entropy(r, &buf, 32, 16, 0);
if (num == 0)
return;
- } else
+ } else {
_extract_crng(&primary_crng, buf.block);
+ _crng_backtrack_protect(&primary_crng, buf.block,
+ CHACHA20_KEY_SIZE);
+ }
spin_lock_irqsave(&primary_crng.lock, flags);
for (i = 0; i < 8; i++) {
unsigned long rv;
@@ -889,9 +893,46 @@ static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
_extract_crng(crng, out);
}
+/*
+ * Use the leftover bytes from the CRNG block output (if there is
+ * enough) to mutate the CRNG key to provide backtracking protection.
+ */
+static void _crng_backtrack_protect(struct crng_state *crng,
+ __u8 tmp[CHACHA20_BLOCK_SIZE], int used)
+{
+ unsigned long flags;
+ __u32 *s, *d;
+ int i;
+
+ used = round_up(used, sizeof(__u32));
+ if (used + CHACHA20_KEY_SIZE > CHACHA20_BLOCK_SIZE) {
+ extract_crng(tmp);
+ used = 0;
+ }
+ spin_lock_irqsave(&crng->lock, flags);
+ 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(__u8 tmp[CHACHA20_BLOCK_SIZE], int used)
+{
+ struct crng_state *crng = NULL;
+
+#ifdef CONFIG_NUMA
+ if (crng_node_pool)
+ crng = crng_node_pool[numa_node_id()];
+ if (crng == NULL)
+#endif
+ crng = &primary_crng;
+ _crng_backtrack_protect(crng, tmp, used);
+}
+
static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
{
- ssize_t ret = 0, i;
+ ssize_t ret = 0, i = CHACHA20_BLOCK_SIZE;
__u8 tmp[CHACHA20_BLOCK_SIZE];
int large_request = (nbytes > 256);
@@ -916,6 +957,7 @@ static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
buf += i;
ret += i;
}
+ crng_backtrack_protect(tmp, i);
/* Wipe data just written to memory */
memzero_explicit(tmp, sizeof(tmp));
@@ -1473,8 +1515,10 @@ void get_random_bytes(void *buf, int nbytes)
if (nbytes > 0) {
extract_crng(tmp);
memcpy(buf, tmp, nbytes);
- memzero_explicit(tmp, nbytes);
- }
+ crng_backtrack_protect(tmp, nbytes);
+ } else
+ crng_backtrack_protect(tmp, CHACHA20_BLOCK_SIZE);
+ memzero_explicit(tmp, sizeof(tmp));
}
EXPORT_SYMBOL(get_random_bytes);
--
2.5.0
next prev parent reply other threads:[~2016-06-13 15:49 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-13 15:48 [PATCH-v4 0/7] random: replace urandom pool with a CRNG Theodore Ts'o
2016-06-13 15:48 ` [PATCH 1/7] random: initialize the non-blocking pool via add_hwgenerator_randomness() Theodore Ts'o
2016-06-13 15:48 ` [PATCH 2/7] random: print a warning for the first ten uninitialized random users Theodore Ts'o
2016-06-13 15:48 ` [PATCH 3/7] random: add interrupt callback to VMBus IRQ handler Theodore Ts'o
2016-06-13 15:48 ` [PATCH 4/7] random: properly align get_random_int_hash Theodore Ts'o
2016-06-13 15:48 ` [PATCH 5/7] random: replace non-blocking pool with a Chacha20-based CRNG Theodore Ts'o
2016-06-13 18:00 ` Stephan Mueller
2016-06-13 19:03 ` Theodore Ts'o
2016-06-15 14:59 ` Herbert Xu
2016-06-19 23:18 ` Theodore Ts'o
2016-06-20 1:25 ` Herbert Xu
2016-06-20 5:02 ` Theodore Ts'o
2016-06-20 5:19 ` Herbert Xu
2016-06-20 15:01 ` Theodore Ts'o
2016-06-20 15:49 ` Stephan Mueller
2016-06-20 18:52 ` H. Peter Anvin
2016-06-20 23:48 ` Theodore Ts'o
2016-06-26 18:47 ` Pavel Machek
2016-06-26 19:10 ` Stephan Mueller
2016-06-26 22:51 ` Theodore Ts'o
2016-06-13 15:48 ` [PATCH 6/7] random: make /dev/urandom scalable for silly userspace programs Theodore Ts'o
2016-08-21 9:53 ` Jan Varho
2016-08-21 11:36 ` Theodore Ts'o
2016-06-13 15:48 ` Theodore Ts'o [this message]
2016-06-26 18:47 ` [PATCH 7/7] random: add backtracking protection to the CRNG Pavel Machek
2016-06-26 23:05 ` Theodore Ts'o
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