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=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 61063C47425 for ; Thu, 1 Oct 2020 11:54:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2B44121481 for ; Thu, 1 Oct 2020 11:54:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601553253; bh=ehSrBxJgqmsMMkm4bs4LW9SlzHsN1fYrrmWK3mPVO04=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=H+OjSXnpbOH1yTr/Kyc8oZ8O+wI4euilVaS0U8WCVxgjgPglZs5fi7c20AsD1/yl1 EeSVfVUevq4YYorJVEZ2hxAzSxjfMWvM1Xy2hlI61fHMqXPm51/t7xM5b8Mon3HhzP m8EQevzV/Xue+FHooEzHcMI3HisaFco4/H3OzJqI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731921AbgJALyH (ORCPT ); Thu, 1 Oct 2020 07:54:07 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:35197 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731767AbgJALyE (ORCPT ); Thu, 1 Oct 2020 07:54:04 -0400 Received: by mail-wr1-f67.google.com with SMTP id e16so5363908wrm.2; Thu, 01 Oct 2020 04:54:02 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=QjEMtQV4+mKov3RyEvL2p8vci/KPjj4gyXV5HFr4bPc=; b=b4h+AThi7lMNfqipaCF70dryQ7rghrc3kGH1kfJ6QRJ6sbselZbvESFc7c2r9ARXrS hvd/f09+8mFbKTppTX0Gp8WpI0fOqZ+AtHIfqe+qZzbYwWgZmsai1K1qpJMwgu4zokES 7WWHvJ1GCbsFsJsI9v/qyfS9IsdtIF6u87ltsj7BbNHfBPeDnyknNcdvmHXi4Vg4j33I gNrdWb6PU6pLFZeIgu5hFxFvq3qc9s3T/vKiL5QEIh4tlU3wcOO4CvPSsg5Qkj2JTjKb 51qvgS3DyXSkPYqP+HJKGMx+X4d3CmNv4ZCd74dTFfnQaeNRq00ilKV8cTM+Rnmgkl68 /TMQ== X-Gm-Message-State: AOAM530PBmLvpo1qCWXc+J4RhnhKQpRLRldKN2dJooS6H6olKBy89CKY L7NVomr+j6zXnFs21cWRpIw= X-Google-Smtp-Source: ABdhPJzfEPCoC4dSc6yo8yiwrjfjgNGFM6Ov812hYIpeuIQMHakZq8GmSq7lhhZTC7m73NSlbg0kRA== X-Received: by 2002:a5d:6404:: with SMTP id z4mr8995115wru.423.1601553241933; Thu, 01 Oct 2020 04:54:01 -0700 (PDT) Received: from liuwe-devbox-debian-v2 ([51.145.34.42]) by smtp.gmail.com with ESMTPSA id s19sm5286587wmc.0.2020.10.01.04.54.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Oct 2020 04:54:01 -0700 (PDT) Date: Thu, 1 Oct 2020 11:53:59 +0000 From: Wei Liu To: Vitaly Kuznetsov Cc: Sasha Levin , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, mikelley@microsoft.com, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, stable@kernel.org, kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, wei.liu@kernel.org Subject: Re: [PATCH] x86/hyper-v: guard against cpu mask changes in hyperv_flush_tlb_others() Message-ID: <20201001115359.6jhhrybemnhizgok@liuwe-devbox-debian-v2> References: <20201001013814.2435935-1-sashal@kernel.org> <87o8lm9te3.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87o8lm9te3.fsf@vitty.brq.redhat.com> User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Thu, Oct 01, 2020 at 11:40:04AM +0200, Vitaly Kuznetsov wrote: > Sasha Levin writes: > > > cpumask can change underneath us, which is generally safe except when we > > call into hv_cpu_number_to_vp_number(): if cpumask ends up empty we pass > > num_cpu_possible() into hv_cpu_number_to_vp_number(), causing it to read > > garbage. As reported by KASAN: > > > > [ 83.504763] BUG: KASAN: slab-out-of-bounds in hyperv_flush_tlb_others (include/asm-generic/mshyperv.h:128 arch/x86/hyperv/mmu.c:112) > > [ 83.908636] Read of size 4 at addr ffff888267c01370 by task kworker/u8:2/106 > > [ 84.196669] CPU: 0 PID: 106 Comm: kworker/u8:2 Tainted: G W 5.4.60 #1 > > [ 84.196669] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090008 12/07/2018 > > [ 84.196669] Workqueue: writeback wb_workfn (flush-8:0) > > [ 84.196669] Call Trace: > > [ 84.196669] dump_stack (lib/dump_stack.c:120) > > [ 84.196669] print_address_description.constprop.0 (mm/kasan/report.c:375) > > [ 84.196669] __kasan_report.cold (mm/kasan/report.c:507) > > [ 84.196669] kasan_report (arch/x86/include/asm/smap.h:71 mm/kasan/common.c:635) > > [ 84.196669] hyperv_flush_tlb_others (include/asm-generic/mshyperv.h:128 arch/x86/hyperv/mmu.c:112) > > [ 84.196669] flush_tlb_mm_range (arch/x86/include/asm/paravirt.h:68 arch/x86/mm/tlb.c:798) > > [ 84.196669] ptep_clear_flush (arch/x86/include/asm/tlbflush.h:586 mm/pgtable-generic.c:88) > > > > Fixes: 0e4c88f37693 ("x86/hyper-v: Use cheaper HVCALL_FLUSH_VIRTUAL_ADDRESS_{LIST,SPACE} hypercalls when possible") > > Cc: Vitaly Kuznetsov > > Cc: stable@kernel.org > > Signed-off-by: Sasha Levin > > --- > > arch/x86/hyperv/mmu.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c > > index 5208ba49c89a9..b1d6afc5fc4a3 100644 > > --- a/arch/x86/hyperv/mmu.c > > +++ b/arch/x86/hyperv/mmu.c > > @@ -109,7 +109,9 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus, > > * must. We will also check all VP numbers when walking the > > * supplied CPU set to remain correct in all cases. > > */ > > - if (hv_cpu_number_to_vp_number(cpumask_last(cpus)) >= 64) > > + int last = cpumask_last(cpus); > > + > > + if (last < num_possible_cpus() && hv_cpu_number_to_vp_number(last) >= 64) > > goto do_ex_hypercall; > > In case 'cpus' can end up being empty (I'm genuinely suprised it can) > the check is mandatory indeed. I would, however, just return directly in > this case: > > if (last < num_possible_cpus()) > return; I think you want last >= num_possible_cpus() here? A more important question is, if the mask can change willy-nilly, what is stopping it from changing between these checks? I.e. is there still a windows that hv_cpu_number_to_vp_number(last) can return garbage? Wei. > > if (hv_cpu_number_to_vp_number(last) >= 64) > goto do_ex_hypercall; > > as there's nothing to flush, no need to call into > hyperv_flush_tlb_others_ex(). > > Anyway, the fix seems to be correct, so > > Reviewed-by: Vitaly Kuznetsov > > > > > for_each_cpu(cpu, cpus) { > > -- > Vitaly >