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=-12.3 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 81D09C4363D for ; Mon, 5 Oct 2020 14:58:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E94C2078A for ; Mon, 5 Oct 2020 14:58:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601909938; bh=ZWNmrkKLhMQn6xnGg4I0pWPYsJ37uroHKwdVL5gZBBM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=qwIZ73PYtu27UT4d8VCdDgSYMe009gYVS8qeXHvszW9eZ7IqPXZlZl3OCDdOhRjz0 vKYzdPH+JE14/j5H8ZAQWlrV7H4kKHKzCBfxzm8xORJibon1aKWX2V/14XI+hYT/GD pDqN8leBwt6C6cAAkjNRPZTb5GsgfENPS6V+gXWw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726087AbgJEO65 (ORCPT ); Mon, 5 Oct 2020 10:58:57 -0400 Received: from mail-wr1-f66.google.com ([209.85.221.66]:40182 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725936AbgJEO64 (ORCPT ); Mon, 5 Oct 2020 10:58:56 -0400 Received: by mail-wr1-f66.google.com with SMTP id j2so9959587wrx.7; Mon, 05 Oct 2020 07:58:54 -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=arf4WDavo4mH+NimIUSRraS6XCsUtA2SCJsUc8RhY20=; b=lSk5q0B9Ef+s7sW2sGAkfZ6mHMVcJkTJts3bZlIhNwpE5vdyn0dxqpgLYe0FN6zvRf H/p0St/fKzqyDkiLURnXXrIzPmqy4z0I6PHJWt0DMrOuW5SAlJLUA0SmjRximKe9a3Mq OON5R2z5dfB+KnJg7PhE5LTF5ZxSvLHFn8icT3JBmRUW7uktOGvRWdpC8KfZtoffIJie +ICStHwCQxxJIAcehyTdHTNmjQjSUvMOPUiE3vEhi12W6qxSiUvN9N0J0IE/RIZWCScQ E9KGx9xnPzws1iEDnGtHEhF0y4foHK5Qu2iUKr0FOTvK7WX1nPEzkNs3sXDsx81jqBzp fAcA== X-Gm-Message-State: AOAM532Uorhy52nbt3zM7n9wwS3FGN5QiILfH7wgRCJFELRfCcrJPSMo oaNr2eWo+lvahrOZwlw+l4KVuAxGc9E= X-Google-Smtp-Source: ABdhPJwsmYfIdZo5A7MWOv7wthty+N7BmpngScIGBIplUKSh8CDx3xU7kBEDNGlby8jxVEiqswcdew== X-Received: by 2002:adf:f44d:: with SMTP id f13mr17984801wrp.224.1601909933711; Mon, 05 Oct 2020 07:58:53 -0700 (PDT) Received: from liuwe-devbox-debian-v2 ([51.145.34.42]) by smtp.gmail.com with ESMTPSA id t16sm2961wmi.18.2020.10.05.07.58.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Oct 2020 07:58:53 -0700 (PDT) Date: Mon, 5 Oct 2020 14:58:51 +0000 From: Wei Liu To: Michael Kelley Cc: Sasha Levin , Wei Liu , vkuznets , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "x86@kernel.org" , "hpa@zytor.com" , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "stable@kernel.org" , KY Srinivasan , Haiyang Zhang , Stephen Hemminger Subject: Re: [PATCH] x86/hyper-v: guard against cpu mask changes in hyperv_flush_tlb_others() Message-ID: <20201005145851.hdyaeqo3celt2wtr@liuwe-devbox-debian-v2> References: <20201001013814.2435935-1-sashal@kernel.org> <87o8lm9te3.fsf@vitty.brq.redhat.com> <20201001115359.6jhhrybemnhizgok@liuwe-devbox-debian-v2> <20201001130400.GE2415204@sasha-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 03, 2020 at 05:40:15PM +0000, Michael Kelley wrote: > From: Sasha Levin Sent: Thursday, October 1, 2020 6:04 AM > > > > On Thu, Oct 01, 2020 at 11:53:59AM +0000, Wei Liu wrote: > > >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) > > > > I was just as surprised as you and spent the good part of a day > > debugging this. However, a: > > > > WARN_ON(cpumask_empty(cpus)); > > > > triggers at that line of code even though we check for cpumask_empty() > > at the entry of the function. > > What does the call stack look like when this triggers? I'm curious about > the path where the 'cpus' could be changing while the flush call is in > progress. > > I wonder if CPUs could ever be added to the mask? Removing CPUs can > be handled with some care because an unnecessary flush doesn't hurt > anything. But adding CPUs has serious correctness problems. > The cpumask_empty check is done before disabling irq. Is it possible the mask is modified by an interrupt? If there is a reliable way to trigger this bug, we may be able to test the following patch. diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c index 5208ba49c89a..23fa08d24c1a 100644 --- a/arch/x86/hyperv/mmu.c +++ b/arch/x86/hyperv/mmu.c @@ -66,11 +66,13 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus, if (!hv_hypercall_pg) goto do_native; - if (cpumask_empty(cpus)) - return; - local_irq_save(flags); + if (cpumask_empty(cpus)) { + local_irq_restore(flags); + return; + } + flush_pcpu = (struct hv_tlb_flush **) this_cpu_ptr(hyperv_pcpu_input_arg);