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 CB0B4C001DF for ; Tue, 25 Jul 2023 15:56:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231819AbjGYP4t (ORCPT ); Tue, 25 Jul 2023 11:56:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37520 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230283AbjGYP4r (ORCPT ); Tue, 25 Jul 2023 11:56:47 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95642212F for ; Tue, 25 Jul 2023 08:56:35 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id 3f1490d57ef6-cf4cb742715so6434521276.2 for ; Tue, 25 Jul 2023 08:56:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1690300594; x=1690905394; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=192puc/qm0mn1nvHJQQuZAuevgCM+LQ+IAyFRTMu9UI=; b=oZHJ5tW0tbTnU+JGXamk16o2P6x09kfVHnHealC4waOtd6uXLmoIBdHIRK87U6tn0V O7wXly7QjyM+RqIH00hD9j1PbLvZ5JX0+cSSJRodxGhdLozQ2FNv3xhpnZ+sOcMNjHpe n2JcqSB6sFrK/WeSbuokR9t4Fic7FZrd8pfhMgNmPv+Bl5wmLR/a+DIc0biujeuW0iHU M9Eyd0CSXzzqdiUe7RZx6meZy/OfW3ddKDQaS7Hl0QGSh7UAkW1TPUEOfqbrzXVHdP06 8jVzjfcMBdqEJqqK0+gT7/L/6GDvRN7t9iuWU/pmK/HDM13UVjs+VuNn0FQw2or4fDn6 1Z7g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690300594; x=1690905394; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=192puc/qm0mn1nvHJQQuZAuevgCM+LQ+IAyFRTMu9UI=; b=WgiTRPHz8vkpFOX1TWMag5gWssWISCyZNKyU5EK2JrnegSv4CdJ/KvXmvRV2S1cUH4 3Bt9rVneaOmE1wgGThUvnBEjdas5vcXfG2FsCIhfnAd5PcU9nAABcw7Z3OFGlkNVKohW 8h7XEuAUB9u0JoFqhTf+4PjL9vrCAuuR3NcJCXrLfhyxgl65PPCg8Mowg5nBQLaMuOdG E3Dqe7StZyxgRUefEv32616DpzVBhbyN4/aBhG+nobyeCtBaHTr/33pszrAaYNPnQM2S jwDLQYAQsd0ykOeBPhIAv7vs+TzvdneUZjOkaAm5+PxTFygXhqVrxxOxdt5JY6d2lw/L Q4BA== X-Gm-Message-State: ABy/qLag3sYYcZ680RdmXtlHdigrhryi6ZwkEaAo0uUzTgwPyfHvpdk5 g68VomHjju5DwY+8lIlNFUWY7JXiZ0M= X-Google-Smtp-Source: APBJJlEAyggedsH1gCoghZnma/qZapoi1yuUBu5b3Q+lCrrgQv4F06/B9A6hcBih6sdIzQsURAg3KiFRP8M= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a25:cc82:0:b0:d0d:cce3:d32d with SMTP id l124-20020a25cc82000000b00d0dcce3d32dmr41470ybf.6.1690300594623; Tue, 25 Jul 2023 08:56:34 -0700 (PDT) Date: Tue, 25 Jul 2023 08:56:32 -0700 In-Reply-To: <20230725103945.wfa5zdupen3oo6xl@linux.intel.com> Mime-Version: 1.0 References: <20230722012350.2371049-1-seanjc@google.com> <20230722012350.2371049-4-seanjc@google.com> <20230725103945.wfa5zdupen3oo6xl@linux.intel.com> Message-ID: Subject: Re: [PATCH 3/5] KVM: x86/mmu: Harden TDP MMU iteration against root w/o shadow page From: Sean Christopherson To: Yu Zhang Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Reima Ishii Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Jul 25, 2023, Yu Zhang wrote: > On Fri, Jul 21, 2023 at 06:23:48PM -0700, Sean Christopherson wrote: > > Explicitly check that tdp_iter_start() is handed a valid shadow page > > to harden KVM against bugs where > > Sorry, where? Gah, I must have seen something shiny when writing the changelog. > It's not about guest using an invisible GFN, it's about a KVM bug, right? Yes, the intent is to guard against a KVM bug, e.g. if KVM managed to get into the TDP MMU with an invalid root, or a root belonging to a shadow MMU. I'll fix the changelog in v2. > > Opportunistically stop the TDP MMU iteration instead of continuing on > > with garbage if the incoming root is bogus. Attempting to walk a garbage > > root is more likely to caused major problems than doing nothing. > > > > Signed-off-by: Sean Christopherson > > --- > > arch/x86/kvm/mmu/tdp_iter.c | 11 ++++++----- > > 1 file changed, 6 insertions(+), 5 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c > > index d2eb0d4f8710..bd30ebfb2f2c 100644 > > --- a/arch/x86/kvm/mmu/tdp_iter.c > > +++ b/arch/x86/kvm/mmu/tdp_iter.c > > @@ -39,13 +39,14 @@ void tdp_iter_restart(struct tdp_iter *iter) > > void tdp_iter_start(struct tdp_iter *iter, struct kvm_mmu_page *root, > > int min_level, gfn_t next_last_level_gfn) > > { > > - int root_level = root->role.level; > > - > > - WARN_ON(root_level < 1); > > - WARN_ON(root_level > PT64_ROOT_MAX_LEVEL); > > + if (WARN_ON_ONCE(!root || (root->role.level < 1) || > > + (root->role.level > PT64_ROOT_MAX_LEVEL))) { > > + iter->valid = false; > > + return; > > + } > > > > I saw many usages of WARN_ON_ONCE() and WARN_ON() in KVM. And just wonder, > is there any criteria for KVM when to use which? Heh, already a step ahead of you :-) https://lore.kernel.org/all/20230721230006.2337941-5-seanjc@google.com