From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 9D7E33858419 for ; Wed, 13 Jul 2022 20:16:06 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 9D7E33858419 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-425-iMHqPL0oPWmJ3tCXASEiOg-1; Wed, 13 Jul 2022 16:16:03 -0400 X-MC-Unique: iMHqPL0oPWmJ3tCXASEiOg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B8EED3C025BF; Wed, 13 Jul 2022 20:16:02 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.60]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DFCF61121314; Wed, 13 Jul 2022 20:16:01 +0000 (UTC) From: Florian Weimer To: Noah Goldstein Cc: Adhemerval Zanella , GNU C Library Subject: Re: [PATCH v9 6/9] x86: Add AVX2 optimized chacha20 References: <20220713173657.516725-1-adhemerval.zanella@linaro.org> <20220713173657.516725-7-adhemerval.zanella@linaro.org> Date: Wed, 13 Jul 2022 22:16:00 +0200 In-Reply-To: (Noah Goldstein's message of "Wed, 13 Jul 2022 11:07:27 -0700") Message-ID: <87cze8zs3j.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-5.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_NUMSUBJECT, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 13 Jul 2022 20:16:07 -0000 * Noah Goldstein: > Since `arc4random ()` might need to read from /dev/urandom I don't > think this function could ever truly be RTM safe so we may not care. > > If im missing something we do want to support RTM, should there be a > '!CPU_FEATURE_USABLE_P (cpu_features, RTM)' check for the avx2 > implementation? Calling arc4random from a transaction is potentially unsafe anyway because it may act as an oracle that reveals the internal PRNG state. The application needs to avoid that. I think we can use the AVX2 implementation even with RTM enabled. Thanks, Florian