From patchwork Tue Jun 6 17:47:52 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 9769369 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id C688C60393 for ; Tue, 6 Jun 2017 17:48:43 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C1CE42849E for ; Tue, 6 Jun 2017 17:48:43 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B6999284E4; Tue, 6 Jun 2017 17:48:43 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_MED,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id A07012849E for ; Tue, 6 Jun 2017 17:48:42 +0000 (UTC) Received: (qmail 32656 invoked by uid 550); 6 Jun 2017 17:48:23 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 32597 invoked from network); 6 Jun 2017 17:48:21 -0000 DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=zx2c4.com; h=from:to:cc :subject:date:message-id:in-reply-to:references; s=mail; bh=gsZO oOe/C5FahZT0pAD8J4akcjM=; b=DSkM9ObezkqFywUuZA25BcSmkQLH78lTuPuF 2JXCN3RfaK0RC8XjM7OEdVdJ32UYnB5y5Qx658qF3qjqku7Tq8NLYo2Aljd4aIZa 1OQNMWZ2xhXgficqD+CSxiQHdzuOEfwSywcTFRq+tRVKU4pwo2eeAfGlGmtFBUtY RVB1WwXkKR7Dkdxhs9sT8cAnBpfN3obLRBJF70RqScV74gZZhaKyC8QClrpCutA5 SB0ksop2VkzrnbW+f25l6GhD3S6xbKi9eqG03zw+FpXQwAouxVdJKYFiGKpbrjEh I1//T9IXJtVTbryndh/GQYPI0JoNy8X9r/Lto5E6Ibf3DvYVNA== From: "Jason A. Donenfeld" To: Theodore Ts'o , Linux Crypto Mailing List , LKML , kernel-hardening@lists.openwall.com, Greg Kroah-Hartman , David Miller , Eric Biggers Cc: "Jason A. Donenfeld" Date: Tue, 6 Jun 2017 19:47:52 +0200 Message-Id: <20170606174804.31124-2-Jason@zx2c4.com> X-Mailer: git-send-email 2.13.0 In-Reply-To: <20170606174804.31124-1-Jason@zx2c4.com> References: <20170606174804.31124-1-Jason@zx2c4.com> Subject: [kernel-hardening] [PATCH v4 01/13] random: invalidate batched entropy after crng init X-Virus-Scanned: ClamAV using ClamSMTP It's possible that get_random_{u32,u64} is used before the crng has initialized, in which case, its output might not be cryptographically secure. For this problem, directly, this patch set is introducing the *_wait variety of functions, but even with that, there's a subtle issue: what happens to our batched entropy that was generated before initialization. Prior to this commit, it'd stick around, supplying bad numbers. After this commit, we force the entropy to be re-extracted after each phase of the crng has initialized. In order to avoid a race condition with the position counter, we introduce a simple rwlock for this invalidation. Since it's only during this awkward transition period, after things are all set up, we stop using it, so that it doesn't have an impact on performance. This should probably be backported to 4.11. (Also: adding my copyright to the top. With the patch series from January, this patch, and then the ones that come after, I think there's a relevant amount of code in here to add my name to the top.) Signed-off-by: Jason A. Donenfeld Cc: Greg Kroah-Hartman --- drivers/char/random.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/drivers/char/random.c b/drivers/char/random.c index 0ab024918907..2291e6224ed3 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1,6 +1,9 @@ /* * random.c -- A strong random number generator * + * Copyright (C) 2017 Jason A. Donenfeld . All + * Rights Reserved. + * * Copyright Matt Mackall , 2003, 2004, 2005 * * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All @@ -762,6 +765,8 @@ static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait); static struct crng_state **crng_node_pool __read_mostly; #endif +static void invalidate_batched_entropy(void); + static void crng_initialize(struct crng_state *crng) { int i; @@ -799,6 +804,7 @@ static int crng_fast_load(const char *cp, size_t len) cp++; crng_init_cnt++; len--; } if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { + invalidate_batched_entropy(); crng_init = 1; wake_up_interruptible(&crng_init_wait); pr_notice("random: fast init done\n"); @@ -836,6 +842,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r) memzero_explicit(&buf, sizeof(buf)); crng->init_time = jiffies; if (crng == &primary_crng && crng_init < 2) { + invalidate_batched_entropy(); crng_init = 2; process_random_ready_list(); wake_up_interruptible(&crng_init_wait); @@ -2019,6 +2026,7 @@ struct batched_entropy { }; unsigned int position; }; +static rwlock_t batched_entropy_reset_lock = __RW_LOCK_UNLOCKED(batched_entropy_reset_lock); /* * Get a random word for internal kernel use only. The quality of the random @@ -2029,6 +2037,8 @@ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64); u64 get_random_u64(void) { u64 ret; + bool use_lock = crng_init < 2; + unsigned long flags; struct batched_entropy *batch; #if BITS_PER_LONG == 64 @@ -2041,11 +2051,15 @@ u64 get_random_u64(void) #endif batch = &get_cpu_var(batched_entropy_u64); + if (use_lock) + read_lock_irqsave(&batched_entropy_reset_lock, flags); if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) { extract_crng((u8 *)batch->entropy_u64); batch->position = 0; } ret = batch->entropy_u64[batch->position++]; + if (use_lock) + read_unlock_irqrestore(&batched_entropy_reset_lock, flags); put_cpu_var(batched_entropy_u64); return ret; } @@ -2055,22 +2069,45 @@ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32); u32 get_random_u32(void) { u32 ret; + bool use_lock = crng_init < 2; + unsigned long flags; struct batched_entropy *batch; if (arch_get_random_int(&ret)) return ret; batch = &get_cpu_var(batched_entropy_u32); + if (use_lock) + read_lock_irqsave(&batched_entropy_reset_lock, flags); if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) { extract_crng((u8 *)batch->entropy_u32); batch->position = 0; } ret = batch->entropy_u32[batch->position++]; + if (use_lock) + read_unlock_irqrestore(&batched_entropy_reset_lock, flags); put_cpu_var(batched_entropy_u32); return ret; } EXPORT_SYMBOL(get_random_u32); +/* It's important to invalidate all potential batched entropy that might + * be stored before the crng is initialized, which we can do lazily by + * simply resetting the counter to zero so that it's re-extracted on the + * next usage. */ +static void invalidate_batched_entropy(void) +{ + int cpu; + unsigned long flags; + + write_lock_irqsave(&batched_entropy_reset_lock, flags); + for_each_possible_cpu (cpu) { + per_cpu_ptr(&batched_entropy_u32, cpu)->position = 0; + per_cpu_ptr(&batched_entropy_u64, cpu)->position = 0; + } + write_unlock_irqrestore(&batched_entropy_reset_lock, flags); +} + /** * randomize_page - Generate a random, page aligned address * @start: The smallest acceptable address the caller will take.