From patchwork Tue Jun 6 17:48:04 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: 9769417 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 C93BE6035D for ; Tue, 6 Jun 2017 17:50:19 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C5689223A6 for ; Tue, 6 Jun 2017 17:50:19 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B9FB726E1A; Tue, 6 Jun 2017 17:50:19 +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 C3D55223A6 for ; Tue, 6 Jun 2017 17:50:18 +0000 (UTC) Received: (qmail 5171 invoked by uid 550); 6 Jun 2017 17:48:51 -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 1874 invoked from network); 6 Jun 2017 17:48:37 -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=BsdC aIk2Rn0rGBp8DtWuc9y5Ki4=; b=yE0OqxkyFgo05omtK84OEgQv+odY+jLEuXnX J9DImgZDBkphfyvmj1xVBF3NtmCqE1qc3H0uENc/8uqvUpn410V9xuvcD3YUPT4D WRgiIMWtgP4Y7sh4R6S9Yn0d7apH36fEXmZgFaQ3CoAGmUbzWNbo0iUoSj0wJmqW v6dQhEyLyiJ/VxdMa4PphMB6CM/erfM4tpsWdS4LAV/EhXjZj1Oq55pfYKWI9RNl 8CNec/eVO97oyfOt1uFzcX1N1EeZ6jlHVs9gJQq8pMHtoDT4ADdBAT8LJ/wNwrlX xDcNwXcJz52e0PqA5IXd+Yu7NftOgJrLIZxfZ9468zT9o1Pmvg== 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 19:48:04 +0200 Message-Id: <20170606174804.31124-14-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 13/13] random: warn when kernel uses unseeded randomness X-Virus-Scanned: ClamAV using ClamSMTP This enables an important dmesg notification about when drivers have used the crng without it being seeded first. Prior, these errors would occur silently, and so there hasn't been a great way of diagnosing these types of bugs for obscure setups. By adding this as a config option, we can leave it on by default, so that we learn where these issues happen, in the field, will still allowing some people to turn it off, if they really know what they're doing and do not want the log entries. However, we don't leave it _completely_ by default. An earlier version of this patch simply had `default y`. I'd really love that, but it turns out, this problem with unseeded randomness being used is really quite present and is going to take a long time to fix. Thus, as a compromise between log-messages-for-all and nobody-knows, this is `default y`, except it is also `depends on DEBUG_KERNEL`. This will ensure that the curious see the messages while others don't have to. Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 15 +++++++++++++-- lib/Kconfig.debug | 16 ++++++++++++++++ 2 files changed, 29 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 36cdb2406610..33a9ec86d101 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -288,7 +288,6 @@ #define SEC_XFER_SIZE 512 #define EXTRACT_SIZE 10 -#define DEBUG_RANDOM_BOOT 0 #define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long)) @@ -1477,7 +1476,7 @@ void get_random_bytes(void *buf, int nbytes) { __u8 tmp[CHACHA20_BLOCK_SIZE]; -#if DEBUG_RANDOM_BOOT > 0 +#ifdef CONFIG_WARN_UNSEEDED_RANDOM if (!crng_ready()) printk(KERN_NOTICE "random: %pF get_random_bytes called " "with crng_init = %d\n", (void *) _RET_IP_, crng_init); @@ -2071,6 +2070,12 @@ u64 get_random_u64(void) return ret; #endif +#ifdef CONFIG_WARN_UNSEEDED_RANDOM + if (!crng_ready()) + printk(KERN_NOTICE "random: %pF get_random_u64 called " + "with crng_init = %d\n", (void *) _RET_IP_, crng_init); +#endif + batch = &get_cpu_var(batched_entropy_u64); if (use_lock) read_lock_irqsave(&batched_entropy_reset_lock, flags); @@ -2097,6 +2102,12 @@ u32 get_random_u32(void) if (arch_get_random_int(&ret)) return ret; +#ifdef CONFIG_WARN_UNSEEDED_RANDOM + if (!crng_ready()) + printk(KERN_NOTICE "random: %pF get_random_u32 called " + "with crng_init = %d\n", (void *) _RET_IP_, crng_init); +#endif + batch = &get_cpu_var(batched_entropy_u32); if (use_lock) read_lock_irqsave(&batched_entropy_reset_lock, flags); diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index e4587ebe52c7..c4159605bfbf 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1209,6 +1209,22 @@ config STACKTRACE It is also used by various kernel debugging features that require stack trace generation. +config WARN_UNSEEDED_RANDOM + bool "Warn when kernel uses unseeded randomness" + default y + depends on DEBUG_KERNEL + help + Some parts of the kernel contain bugs relating to their use of + cryptographically secure random numbers before it's actually possible + to generate those numbers securely. This setting ensures that these + flaws don't go unnoticed, by enabling a message, should this ever + occur. This will allow people with obscure setups to know when things + are going wrong, so that they might contact developers about fixing + it. + + Say Y here, unless you simply do not care about using unseeded + randomness and do not want a potential warning message in your logs. + config DEBUG_KOBJECT bool "kobject debugging" depends on DEBUG_KERNEL