From mboxrd@z Thu Jan 1 00:00:00 1970 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 B7FDCC04A6A for ; Tue, 1 Aug 2023 18:52:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231773AbjHASwl (ORCPT ); Tue, 1 Aug 2023 14:52:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34592 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231205AbjHASwi (ORCPT ); Tue, 1 Aug 2023 14:52:38 -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 B1B5526AF; Tue, 1 Aug 2023 11:52:29 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E8CC26168C; Tue, 1 Aug 2023 18:52:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECE18C433C7; Tue, 1 Aug 2023 18:52:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690915948; bh=6xMg5NjfuoUSj5drampUB+oWq/nZBffbC1u9O3r6w58=; h=Date:To:Cc:Subject:From:References:In-Reply-To:From; b=nVSBZCT7NGQU/KvgBbPbDZlWg0KHHTxYw66AIKWEYaqzfFqjTTX/Mx/aZbu7pMkNs yl3QxjQBqVUgQq1y7jI2ctSifMAPV9HLd7hp6a5/BAUZZB6bfl35gt/c37fWoZ5JiX tprK7DIAZiQeCwrWos2TSkMP6CpWl2ocoVkfhyqH55PSSN4hPTVoHEkSW2UMNkRnEj S3RuJN3LNXo1Cz0ORk52JfFH1+fsk7S/eXI0MQxFFppbab0SC481XCOhQM6xY6P45G 9oKCAcbkUJ+JArmBv8OlOxOPDjg/eW+cvkXP43dWN5ZySbzsGItuDl1Y+29/n9k3IZ Fr/y1h9WfvdxQ== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 01 Aug 2023 21:52:23 +0300 Message-Id: To: "Mario Limonciello" , "Jason A. Donenfeld" , "Linus Torvalds" Cc: , "Daniil Stas" , , , , , Subject: Re: [PATCH 1/1] tpm: disable hwrng for fTPM on some AMD designs From: "Jarkko Sakkinen" X-Mailer: aerc 0.14.0 References: <20230727183805.69c36d6e@g14> <20230727193949.55c18805@g14> <65a1c307-826d-4ca3-0336-07a185684e5d@amd.com> <20230727195019.41abb48d@g14> <67eefe98-e6df-e152-3169-44329e22478d@amd.com> <20230727200527.4080c595@g14> <105b9d13-cedd-7d3c-1f29-2c65199f1de7@amd.com> <61b363bc-286a-535c-27da-0f52673768ad@amd.com> In-Reply-To: <61b363bc-286a-535c-27da-0f52673768ad@amd.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue Aug 1, 2023 at 6:04 AM EEST, Mario Limonciello wrote: > On 7/31/23 18:40, Jason A. Donenfeld wrote: > > Hi all, > >=20 > > I've been tracking this issue with Mario on various threads and > > bugzilla for a while now. My suggestion over at bugzilla was to just > > disable all current AMD fTPMs by bumping the check for a major version > > number, so that the hardware people can reenable it i it's ever fixed, > > but only if this is something that the hardware people would actually > > respect. As I understand it, Mario was going to check into it and see. > > Failing that, yea, just disabling hwrng on fTPM seems like a fine > > enough thing to do. > >=20 > > The reason I'm not too concerned about that is twofold: > > - Systems with fTPM all have RDRAND anyway, so there's no entropy probl= em. > > - fTPM *probably* uses the same random source as RDRAND -- the > > TRNG_OUT MMIO register -- so it's not really doing much more than what > > we already have available. > > Yeah I have conversations ongoing about this topic, but also I concluded > your suspicion is correct. They both get their values from the=20 > integrated CCP HW IP. > > >=20 > > So this all seems fine. And Jarkko's patch seems more or less the > > straight forward way of disabling it. But with that said, in order of > > priority, maybe we should first try these: > >=20 > > 1) Adjust the version check to a major-place fTPM version that AMD's > > hardware team pinky swears will have this bug fixed. (Though, I can > > already imagine somebody on the list shouting, "we don't trust > > hardware teams to do anything with unreleased stuff!", which could be > > valid.) > > I find it very likely the actual root cause is similar to what Linus=20 > suggested. If that's the case I don't think the bug can be fixed > by just an fTPM fix but would rather require a BIOS fix. > > This to me strengthens the argument to either not register fTPM as RNG=20 > in the first place or just use TPM for boot time entropy. > > > 2) Remove the version check, but add some other query to detect AMD > > fTPM vs realTPM, and ban fTPM. > > AMD doesn't make dTPMs, only fTPMs. It's tempting to try to use=20 > TPM2_PT_VENDOR_TPM_TYPE, but this actually is a vendor specific value. > > I don't see a reliable way in the spec to do this. > > > - Remove the version check, and just check for AMD; this is Jarrko's pa= tch. > > I have a counter-proposal to Jarkko's patch attached. This has two=20 > notable changes: > > 1) It only disables RNG generation in the case of having RDRAND or RDSEED= . > 2) It also matches Intel PTT. > > I still do also think Linus' idea of TPMs only providing boot time=20 > entropy is worth weighing out. You should add something like TPM_CHIP_HWRNG_DISABLED instead and set this in tpm_crb before calling tpm_chip_register(). Nothing else concerning AMD hardware should be done in tpm-chip.c. It should only check TPM_CHIP_HWRNG_DISABLED in the beginning of tpm_add_hwrng(). BR, Jarkko