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=-16.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SHORT_TERM_PRICE, SPF_HELO_NONE,SPF_PASS 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 BF1F4C4320A for ; Tue, 24 Aug 2021 14:23:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F0446127B for ; Tue, 24 Aug 2021 14:23:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237744AbhHXOYg (ORCPT ); Tue, 24 Aug 2021 10:24:36 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:32987 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237496AbhHXOYf (ORCPT ); Tue, 24 Aug 2021 10:24:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1629815030; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=eaKLyjNYVTngBJTCQZRJWzBusqzdu0x0pJPgqNd0ExU=; b=HC2up+d/LPHm547ay1BEyx9UsJLFi/zTJTZjM/TKsmDyrTG1/mCxp7nF+8maVjDaROnt75 gj6qvX7EDZIkuBDhlV+DIrHQqCYDj0mW5SaaSMO/qtWCA4pdYHWGBMJnD526Hr0tlh1qYJ d0S5SOccYo0jIXfimXEJXPp1OPZ5Ci8= Received: from mail-lj1-f198.google.com (mail-lj1-f198.google.com [209.85.208.198]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-30-0BSRh2LCNs2l8yVayUnuqA-1; Tue, 24 Aug 2021 10:23:49 -0400 X-MC-Unique: 0BSRh2LCNs2l8yVayUnuqA-1 Received: by mail-lj1-f198.google.com with SMTP id c9-20020a2ea789000000b001bb60afc5e4so5898003ljf.12 for ; Tue, 24 Aug 2021 07:23:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=eaKLyjNYVTngBJTCQZRJWzBusqzdu0x0pJPgqNd0ExU=; b=raOc2xpb+Ac3oKG6wFiHOpqxSkI1NE94rhOEQzhi9SoIj7JNEb0D1Q9+zsGXiIoKXD FguwWx1IO7EJHZziw9EO528UB+B4BzMYmom2CtWARFVgkOJlalPEPjBDyQodrFI+AJZX R4Bp74zG65PJz/y/uw4CXCl/30sa7WDEIO1ZpJzI708dDzg8GNYTqqNVnWRCeuMDzn6w LV8gknf2vjGJfouoeKlwf7RB0PNSrwVpSB2qCvt9e2V+LC7mHFT3q4zlh0XLFjNZ0mi4 LupiMTpXxabVTL+TWydrDJ89agxXU8flx/adnaHPxbrNr5tzKPOJJHPBN+ACc1SvxIAq W2lg== X-Gm-Message-State: AOAM531Xyeb/vqr92+CNzomSS8D93CxrL3U5lToIs2mY96wEzACHgkn/ mfOyUVXPtiEVWpltw0sZoW/yWE0PsaPqxdbMsxk7KkmR23zDPA6764Jrr4XdqSIdFzVK6L+oMl9 6j9xff3YDYFyP2UHD1ejY52SpZcyO1nRQ1d+z27lK X-Received: by 2002:a05:6512:21b1:: with SMTP id c17mr29522541lft.34.1629815027674; Tue, 24 Aug 2021 07:23:47 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwqBcwBUKtfS96gz3cSbo4cZa2F2q9DeAxMRxLSLPa34KVfe28iJ/ILEaIZ8Byp1A3+/1L8Q21oBe7sOOnYHfs= X-Received: by 2002:a05:6512:21b1:: with SMTP id c17mr29522524lft.34.1629815027394; Tue, 24 Aug 2021 07:23:47 -0700 (PDT) MIME-Version: 1.0 References: <20210823143028.649818-1-vkuznets@redhat.com> <20210823143028.649818-5-vkuznets@redhat.com> <20210823185841.ov7ejn2thwebcwqk@habkost.net> <87mtp7jowv.fsf@vitty.brq.redhat.com> In-Reply-To: <87mtp7jowv.fsf@vitty.brq.redhat.com> From: Eduardo Habkost Date: Tue, 24 Aug 2021 10:23:31 -0400 Message-ID: Subject: Re: [PATCH v2 4/4] KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect() To: Vitaly Kuznetsov Cc: kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , "Dr. David Alan Gilbert" , Nitesh Narayan Lal , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 24, 2021 at 3:13 AM Vitaly Kuznetsov wrote: > > Eduardo Habkost writes: > > > On Mon, Aug 23, 2021 at 04:30:28PM +0200, Vitaly Kuznetsov wrote: > >> KASAN reports the following issue: > >> > >> BUG: KASAN: stack-out-of-bounds in kvm_make_vcpus_request_mask+0x174/0x440 [kvm] > >> Read of size 8 at addr ffffc9001364f638 by task qemu-kvm/4798 > >> > >> CPU: 0 PID: 4798 Comm: qemu-kvm Tainted: G X --------- --- > >> Hardware name: AMD Corporation DAYTONA_X/DAYTONA_X, BIOS RYM0081C 07/13/2020 > >> Call Trace: > >> dump_stack+0xa5/0xe6 > >> print_address_description.constprop.0+0x18/0x130 > >> ? kvm_make_vcpus_request_mask+0x174/0x440 [kvm] > >> __kasan_report.cold+0x7f/0x114 > >> ? kvm_make_vcpus_request_mask+0x174/0x440 [kvm] > >> kasan_report+0x38/0x50 > >> kasan_check_range+0xf5/0x1d0 > >> kvm_make_vcpus_request_mask+0x174/0x440 [kvm] > >> kvm_make_scan_ioapic_request_mask+0x84/0xc0 [kvm] > >> ? kvm_arch_exit+0x110/0x110 [kvm] > >> ? sched_clock+0x5/0x10 > >> ioapic_write_indirect+0x59f/0x9e0 [kvm] > >> ? static_obj+0xc0/0xc0 > >> ? __lock_acquired+0x1d2/0x8c0 > >> ? kvm_ioapic_eoi_inject_work+0x120/0x120 [kvm] > >> > >> The problem appears to be that 'vcpu_bitmap' is allocated as a single long > >> on stack and it should really be KVM_MAX_VCPUS long. We also seem to clear > >> the lower 16 bits of it with bitmap_zero() for no particular reason (my > >> guess would be that 'bitmap' and 'vcpu_bitmap' variables in > >> kvm_bitmap_or_dest_vcpus() caused the confusion: while the later is indeed > >> 16-bit long, the later should accommodate all possible vCPUs). > >> > >> Fixes: 7ee30bc132c6 ("KVM: x86: deliver KVM IOAPIC scan request to target vCPUs") > >> Fixes: 9a2ae9f6b6bb ("KVM: x86: Zero the IOAPIC scan request dest vCPUs bitmap") > >> Reported-by: Dr. David Alan Gilbert > >> Signed-off-by: Vitaly Kuznetsov > >> --- > >> arch/x86/kvm/ioapic.c | 10 +++++----- > >> 1 file changed, 5 insertions(+), 5 deletions(-) > >> > >> diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c > >> index ff005fe738a4..92cd4b02e9ba 100644 > >> --- a/arch/x86/kvm/ioapic.c > >> +++ b/arch/x86/kvm/ioapic.c > >> @@ -319,7 +319,7 @@ static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val) > >> unsigned index; > >> bool mask_before, mask_after; > >> union kvm_ioapic_redirect_entry *e; > >> - unsigned long vcpu_bitmap; > >> + unsigned long vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)]; > > > > Is there a way to avoid this KVM_MAX_VCPUS-sized variable on the > > stack? This might hit us back when we increase KVM_MAX_VCPUS to > > a few thousand VCPUs (I was planning to submit a patch for that > > soon). > > What's the short- or mid-term target? Short term target is 2048 (which was already tested). Mid-term target (not tested yet) is 4096, maybe 8192. > > Note, we're allocating KVM_MAX_VCPUS bits (not bytes!) here, this means > that for e.g. 2048 vCPUs we need 256 bytes of the stack only. In case > the target much higher than that, we will need to either switch to > dynamic allocation or e.g. use pre-allocated per-CPU variables and make > this a preempt-disabled region. I, however, would like to understand if > the problem with allocating this from stack is real or not first. Is 256 bytes too much here, or would that be OK? -- Eduardo