From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161096AbcE3FkO (ORCPT ); Mon, 30 May 2016 01:40:14 -0400 Received: from imap.thunk.org ([74.207.234.97]:45498 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161016AbcE3FkM (ORCPT ); Mon, 30 May 2016 01:40:12 -0400 From: "Theodore Ts'o" To: Linux Kernel Developers List Cc: smueller@chronox.de, herbert@gondor.apana.org.au, andi@firstfloor.org, sandyinchina@gmail.com, cryptography@lakedaemon.net, jsd@av8n.com, hpa@zytor.com, linux-crypto@vger.kernel.org, "Theodore Ts'o" Subject: [PATCH 4/5] random: add backtracking protection to the CRNG Date: Mon, 30 May 2016 01:39:24 -0400 Message-Id: <1464586765-14436-5-git-send-email-tytso@mit.edu> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1464586765-14436-1-git-send-email-tytso@mit.edu> References: <1464586765-14436-1-git-send-email-tytso@mit.edu> X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Signed-off-by: Theodore Ts'o --- drivers/char/random.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 47 insertions(+), 5 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index bf370a3..860862f 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 >= 2)) 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); /********************************************************************** @@ -832,8 +833,11 @@ 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; @@ -893,9 +897,44 @@ 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) +{ +#ifdef CONFIG_NUMA + struct crng_state *crng = crng_node_pool[numa_node_id()]; +#else + struct crng_state *crng = &primary_crng; +#endif + + _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); @@ -920,6 +959,7 @@ 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 +1513,10 @@ 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