From patchwork Thu Mar 24 05:09:30 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 12790368 X-Patchwork-Delegate: herbert@gondor.apana.org.au Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D040CC433F5 for ; Thu, 24 Mar 2022 05:09:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236035AbiCXFLN (ORCPT ); Thu, 24 Mar 2022 01:11:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229911AbiCXFLM (ORCPT ); Thu, 24 Mar 2022 01:11:12 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 086D556406; Wed, 23 Mar 2022 22:09:40 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5E3D260ACB; Thu, 24 Mar 2022 05:09:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CF8CBC340EC; Thu, 24 Mar 2022 05:09:38 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="BFq7sgrG" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1648098576; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EIf6XUpZNn8sdyg0oBZDJvT0q3CuPDNYwe6tNeipyVU=; b=BFq7sgrG6Kfp/UxzBKwBahmmqFqH3YoVM+Qfud2jawdf25sDFMS5ZZNAu8qpXokoNlFx9t N5DdkFJh0amprbtj/wuGIjDKsHGxnx/a287nq75d3oICW3EBPjCkCxcFrPnOhKDvH/Ud7t SrCrpkUzzEoPOgpv45UPfC64dWHUKqk= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 1da81b14 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Thu, 24 Mar 2022 05:09:36 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org Cc: "Jason A. Donenfeld" , Theodore Ts'o , Graham Christensen , Ard Biesheuvel , Dominik Brodowski Subject: [PATCH v2] random: treat bootloader trust toggle the same way as cpu trust toggle Date: Wed, 23 Mar 2022 23:09:30 -0600 Message-Id: <20220324050930.207107-1-Jason@zx2c4.com> In-Reply-To: <20220323041123.146459-1-Jason@zx2c4.com> References: <20220323041123.146459-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org If CONFIG_RANDOM_TRUST_CPU is set, the RNG initializes using RDRAND. But, the user can disable (or enable) this behavior by setting `random.trust_cpu=0/1` on the kernel command line. This allows system builders to do reasonable things while avoiding howls from tinfoil hatters. (Or vice versa.) CONFIG_RANDOM_TRUST_BOOTLOADER is basically the same thing, but regards the seed passed via EFI or device tree, which might come from RDRAND or a TPM or somewhere else. In order to allow distros to more easily enable this while avoiding those same howls (or vice versa), this commit adds the corresponding `random.trust_bootloader=0/1` toggle. Cc: Theodore Ts'o Cc: Graham Christensen Reviewed-by: Ard Biesheuvel Reviewed-by: Dominik Brodowski Link: https://github.com/NixOS/nixpkgs/pull/165355 Signed-off-by: Jason A. Donenfeld --- v2 updates the documentation, using the same verbage as the trust_cpu text. Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ drivers/char/Kconfig | 3 ++- drivers/char/random.c | 8 +++++++- 3 files changed, 15 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index c658e5d2d52c..b9d764a49207 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4400,6 +4400,12 @@ fully seed the kernel's CRNG. Default is controlled by CONFIG_RANDOM_TRUST_CPU. + random.trust_bootloader={on,off} + [KNL] Enable or disable trusting the use of the + a seed passed by the bootloader (if available) to + fully seed the kernel's CRNG. Default is controlled + by CONFIG_RANDOM_TRUST_BOOTLOADER. + randomize_kstack_offset= [KNL] Enable or disable kernel stack offset randomization, which provides roughly 5 bits of diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig index 740811893c57..55f48375e3fe 100644 --- a/drivers/char/Kconfig +++ b/drivers/char/Kconfig @@ -449,6 +449,7 @@ config RANDOM_TRUST_BOOTLOADER device randomness. Say Y here to assume the entropy provided by the booloader is trustworthy so it will be added to the kernel's entropy pool. Otherwise, say N here so it will be regarded as device input that - only mixes the entropy pool. + only mixes the entropy pool. This can also be configured at boot with + "random.trust_bootloader=on/off". endmenu diff --git a/drivers/char/random.c b/drivers/char/random.c index 81dab72b611a..40107f8b9e9e 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -949,11 +949,17 @@ static bool drain_entropy(void *buf, size_t nbytes, bool force) **********************************************************************/ static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); +static bool trust_bootloader __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER); static int __init parse_trust_cpu(char *arg) { return kstrtobool(arg, &trust_cpu); } +static int __init parse_trust_bootloader(char *arg) +{ + return kstrtobool(arg, &trust_bootloader); +} early_param("random.trust_cpu", parse_trust_cpu); +early_param("random.trust_bootloader", parse_trust_bootloader); /* * The first collection of entropy occurs at system boot while interrupts @@ -1161,7 +1167,7 @@ EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); */ void add_bootloader_randomness(const void *buf, size_t size) { - if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER)) + if (trust_bootloader) add_hwgenerator_randomness(buf, size, size * 8); else add_device_randomness(buf, size);