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 ADDD9C04E69 for ; Mon, 14 Aug 2023 20:02:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232374AbjHNUBw (ORCPT ); Mon, 14 Aug 2023 16:01:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48108 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232360AbjHNUBd (ORCPT ); Mon, 14 Aug 2023 16:01:33 -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 D7CC410F0 for ; Mon, 14 Aug 2023 13:01:31 -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 6BCBE637E4 for ; Mon, 14 Aug 2023 20:01:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7D273C433C7; Mon, 14 Aug 2023 20:01:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692043290; bh=0Dopu3Kr2QfFROt/Fub5T1L31qUpIl/MqUeM9m/mw6k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gjlvrGkAmq08fLoMQW3+seEBRrwbC1oUNnbb4Sfr5On5w7i9mKc7jnCN5+IeMdKCK awmk8fNryGoirR1GXJYvB4rJZExPxljLRyxGfZIjRzIysuIucF2pI0eeYt2vMvzxxU wJtJGLBLhko//QZBkzOKCUj5TYW9Iw1zW/lpd1LzKNBtQMQ/GaEZXWGPtJL6ZYAXkQ P5YSh3QcG2njGoSpHPANJSFJYXVBIK257zefhVfXqEufK6wBvfd1Or+eeu8iasPu+C GlUzRXRN5xKxZNSRNit5TeWtGhZsLegcudKiHXlZrcXxyFSILZ4FweNvOcVf4ffd7c lZVO49Zeq5vnQ== Date: Mon, 14 Aug 2023 13:01:28 -0700 From: Josh Poimboeuf To: Borislav Petkov Cc: Peter Zijlstra , x86@kernel.org, linux-kernel@vger.kernel.org, David.Kaplan@amd.com, Andrew.Cooper3@citrix.com, gregkh@linuxfoundation.org, nik.borisov@suse.com Subject: Re: [PATCH v2 00/11] Fix up SRSO stuff Message-ID: <20230814200128.ioas5lk2r3yzfkkv@treble> References: <20230814114426.057251214@infradead.org> <20230814164447.GFZNpZ/64H4lENIe94@fat_crate.local> <20230814195153.2zxtp6zx552trgh6@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230814195153.2zxtp6zx552trgh6@treble> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 14, 2023 at 12:51:55PM -0700, Josh Poimboeuf wrote: > On Mon, Aug 14, 2023 at 06:44:47PM +0200, Borislav Petkov wrote: > > On Mon, Aug 14, 2023 at 01:44:26PM +0200, Peter Zijlstra wrote: > > > The one open techinical issue I have with the mitigation is the alignment of > > > the RET inside srso_safe_ret(). The details given for retbleed stated that RET > > > should be on a 64byte boundary, which is not the case here. > > > > I have written this in the hope to make this more clear: > > > > /* > > * Some generic notes on the untraining sequences: > > * > > * They are interchangeable when it comes to flushing potentially wrong > > * RET predictions from the BTB. > > * > > * The SRSO Zen1/2 (MOVABS) untraining sequence is longer than the > > * Retbleed sequence because the return sequence done there > > * (srso_safe_ret()) is longer and the return sequence must fully nest > > * (end before) the untraining sequence. Therefore, the untraining > > * sequence must overlap the return sequence. > > * > > * Regarding alignment - the instructions which need to be untrained, > > * must all start at a cacheline boundary for Zen1/2 generations. That > > * is, both the ret in zen_untrain_ret() and srso_safe_ret() in the > > * srso_untrain_ret() must both be placed at the beginning of > > * a cacheline. > > */ > > It's a good comment, but RET in srso_safe_ret() is still misaligned. > Don't we need something like so? Scratch that, I guess I misread the confusingly worded comment: "both the ret in zen_untrain_ret() and srso_safe_ret()..." to mean the RET in each function. How about: "both the RET in zen_untrain_ret() and the LEA in srso_untrain_ret()" ? -- Josh