From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932155AbcLNEAF (ORCPT ); Tue, 13 Dec 2016 23:00:05 -0500 Received: from frisell.zx2c4.com ([192.95.5.64]:60423 "EHLO frisell.zx2c4.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753230AbcLNEAD (ORCPT ); Tue, 13 Dec 2016 23:00:03 -0500 From: "Jason A. Donenfeld" To: Netdev , kernel-hardening@lists.openwall.com, LKML , linux-crypto@vger.kernel.org Cc: "Jason A. Donenfeld" , Jean-Philippe Aumasson , Ted Tso Subject: [PATCH v2 4/4] random: use siphash24 instead of md5 for get_random_int/long Date: Wed, 14 Dec 2016 04:59:27 +0100 Message-Id: <20161214035927.30004-4-Jason@zx2c4.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20161214035927.30004-1-Jason@zx2c4.com> References: <20161214035927.30004-1-Jason@zx2c4.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This duplicates the current algorithm for get_random_int/long, but uses siphash24 instead. This comes with several benefits. It's certainly faster and more cryptographically secure than MD5. This patch also hashes the pid, entropy, and timestamp as fixed width fields, in order to increase diffusion. The previous md5 algorithm used a per-cpu md5 state, which caused successive calls to the function to chain upon each other. While it's not entirely clear that this kind of chaining is absolutely necessary when using a secure PRF like siphash24, it can't hurt, and the timing of the call chain does add a degree of natural entropy. So, in keeping with this design, instead of the massive per-cpu 64-byte md5 state, there is instead a per-cpu previously returned value for chaining. Signed-off-by: Jason A. Donenfeld Cc: Jean-Philippe Aumasson Cc: Ted Tso --- Changes from v1->v2: - Uses u64 instead of uint64_t - Uses get_cpu_ptr instead of get_cpu_var drivers/char/random.c | 50 +++++++++++++++++++++++++++++++------------------- 1 file changed, 31 insertions(+), 19 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index d6876d506220..61c4b45427dc 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -262,6 +262,7 @@ #include #include #include +#include #include #include @@ -2042,7 +2043,7 @@ struct ctl_table random_table[] = { }; #endif /* CONFIG_SYSCTL */ -static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned; +static u8 random_int_secret[SIPHASH24_KEY_LEN]; int random_int_secret_init(void) { @@ -2050,8 +2051,7 @@ int random_int_secret_init(void) return 0; } -static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash) - __aligned(sizeof(unsigned long)); +static DEFINE_PER_CPU(u64, get_random_int_chaining); /* * Get a random word for internal kernel use only. Similar to urandom but @@ -2061,19 +2061,25 @@ static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash) */ unsigned int get_random_int(void) { - __u32 *hash; unsigned int ret; + struct { + u64 chaining; + unsigned long ts; + unsigned long entropy; + pid_t pid; + } __packed combined; + u64 *chaining; if (arch_get_random_int(&ret)) return ret; - hash = get_cpu_var(get_random_int_hash); - - hash[0] += current->pid + jiffies + random_get_entropy(); - md5_transform(hash, random_int_secret); - ret = hash[0]; - put_cpu_var(get_random_int_hash); - + chaining = get_cpu_ptr(&get_random_int_chaining); + combined.chaining = *chaining; + combined.ts = jiffies; + combined.entropy = random_get_entropy(); + combined.pid = current->pid; + ret = *chaining = siphash24((u8 *)&combined, sizeof(combined), random_int_secret); + put_cpu_ptr(chaining); return ret; } EXPORT_SYMBOL(get_random_int); @@ -2083,19 +2089,25 @@ EXPORT_SYMBOL(get_random_int); */ unsigned long get_random_long(void) { - __u32 *hash; unsigned long ret; + struct { + u64 chaining; + unsigned long ts; + unsigned long entropy; + pid_t pid; + } __packed combined; + u64 *chaining; if (arch_get_random_long(&ret)) return ret; - hash = get_cpu_var(get_random_int_hash); - - hash[0] += current->pid + jiffies + random_get_entropy(); - md5_transform(hash, random_int_secret); - ret = *(unsigned long *)hash; - put_cpu_var(get_random_int_hash); - + chaining = get_cpu_ptr(&get_random_int_chaining); + combined.chaining = *chaining; + combined.ts = jiffies; + combined.entropy = random_get_entropy(); + combined.pid = current->pid; + ret = *chaining = siphash24((u8 *)&combined, sizeof(combined), random_int_secret); + put_cpu_ptr(chaining); return ret; } EXPORT_SYMBOL(get_random_long); -- 2.11.0