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 X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3F06DC43331 for ; Tue, 12 Nov 2019 17:11:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E0012196E for ; Tue, 12 Nov 2019 17:11:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727561AbfKLRLB (ORCPT ); Tue, 12 Nov 2019 12:11:01 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:35030 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726954AbfKLRLA (ORCPT ); Tue, 12 Nov 2019 12:11:00 -0500 Received: from p5b06da22.dip0.t-ipconnect.de ([91.6.218.34] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1iUZgv-0008Dy-2g; Tue, 12 Nov 2019 18:10:57 +0100 Date: Tue, 12 Nov 2019 18:10:56 +0100 (CET) From: Thomas Gleixner To: Andy Lutomirski cc: LKML , X86 ML , Linus Torvalds , Stephen Hemminger , Willy Tarreau , Juergen Gross , Sean Christopherson , "H. Peter Anvin" , Linus Torvalds Subject: Re: [patch V2 08/16] x86/ioperm: Add bitmap sequence number In-Reply-To: Message-ID: References: <20191111220314.519933535@linutronix.de> <20191111223052.292300453@linutronix.de> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 12 Nov 2019, Andy Lutomirski wrote: > On Mon, Nov 11, 2019 at 2:35 PM Thomas Gleixner wrote: > > /* > > + * The bitmap pointer and the sequence number of the last active > > + * bitmap. last_bitmap cannot be dereferenced. It's solely for > > + * comparison. > > + */ > > + struct io_bitmap *last_bitmap; > > + u64 last_sequence; > > + > > + /* > > * Store the dirty size of the last io bitmap offender. The next > > * one will have to do the cleanup as the switch out to a non io > > * bitmap user will just set x86_tss.io_bitmap_base to a value > > Why is all this stuff in the TSS? Would it make more sense in a > percpu variable tss_state? By putting it in the TSS, you're putting > it in cpu_entry_area, which is at least a bit odd if not an actual > security problem. > > And why do you need a last_bitmap pointer? I thin that comparing just > last_sequence should be enough. Keeping last_bitmap around at all is > asking for trouble, since it might point to freed memory. The bitmap pointer is pointless as I said in an earlier reply to Peter. It will go away. The sequence number and the dirty size are surely not a problem leakage wise, but yes, we could put it into a per cpu variable as well. Not sure whether it buys much. > > - memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes, > > - max(tss->io_bitmap_prev_max, iobm->io_bitmap_max)); > > + if (tss->last_bitmap != iobm || > > + tss->last_sequence != iobm->sequence) > > As above, I think this could just be if (tss->last_sequence != > iobm->sequence) or even if (this_cpu_read(cpu_tss_state.iobm_sequence) > != iobm->sequence). Already fixed as per Peter's comments. Thanks, tglx