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 83A45C433EF for ; Mon, 18 Apr 2022 13:33:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242979AbiDRNge (ORCPT ); Mon, 18 Apr 2022 09:36:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54052 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243627AbiDRNKU (ORCPT ); Mon, 18 Apr 2022 09:10:20 -0400 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E483C2E6; Mon, 18 Apr 2022 05:49:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1650286188; x=1681822188; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=ABkdpW+V2FJ0I93fLJrLSjfEAalvHr2mygxY11H9jGg=; b=IJKjD8MoL0bhRXaAvvtYx90ROTn/qZCbxRvS1xY9j2uWNz6xMXHN+029 6ov5hSFrAPgoUhQvIaPyY6MzQcGHDrtyEfKl5dpNGI6p1Bzz1sWtHxEkN EL0VW7zgIYEs+2zRBmBxbNlPEDFSqVcuvkl9TIs9KLfC4dgYmKBfLeweL QLGD8uhuC2z/64eZN4eJO84tEbud/M4rGYWOsyUJtars8scQE+oVUTmLk H1foY43tCH8wyPkI7tfs1CyFGPlPllm4vFuNRYeSI/0KKfg/lIRHHy6V9 6NXFjVeYRP4HIZmaoEB4NnIZqEwdN1TYxXqGalHB+g4MTtrBKKZny7J3X w==; X-IronPort-AV: E=McAfee;i="6400,9594,10320"; a="288598413" X-IronPort-AV: E=Sophos;i="5.90,269,1643702400"; d="scan'208";a="288598413" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2022 05:49:29 -0700 X-IronPort-AV: E=Sophos;i="5.90,269,1643702400"; d="scan'208";a="575558445" Received: from zengguan-mobl1.ccr.corp.intel.com (HELO [10.254.215.57]) ([10.254.215.57]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2022 05:49:22 -0700 Message-ID: <8dee4d22-8b32-e2b0-4f4f-8c1921fce5b3@intel.com> Date: Mon, 18 Apr 2022 20:49:05 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v8 9/9] KVM: VMX: enable IPI virtualization Content-Language: en-US To: Sean Christopherson Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , "kvm@vger.kernel.org" , Dave Hansen , "Luck, Tony" , Kan Liang , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Kim Phillips , Jarkko Sakkinen , Jethro Beekman , "Huang, Kai" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "Hu, Robert" , "Gao, Chao" References: <20220411090447.5928-1-guang.zeng@intel.com> <20220411090447.5928-10-guang.zeng@intel.com> From: Zeng Guang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/15/2022 11:25 PM, Sean Christopherson wrote: > On Mon, Apr 11, 2022, Zeng Guang wrote: >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index d1a39285deab..23fbf52f7bea 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -11180,11 +11180,15 @@ static int sync_regs(struct kvm_vcpu *vcpu) >> >> int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id) >> { >> + int ret = 0; >> + >> if (kvm_check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0) >> pr_warn_once("kvm: SMP vm created on host with unstable TSC; " >> "guest TSC will not be reliable\n"); >> >> - return 0; >> + if (kvm_x86_ops.alloc_ipiv_pid_table) >> + ret = static_call(kvm_x86_alloc_ipiv_pid_table)(kvm); > Add a generic kvm_x86_ops.vcpu_precreate, no reason to make this so specific. > And use KVM_X86_OP_RET0 instead of KVM_X86_OP_OPTIONAL, then this can simply be > > return static_call(kvm_x86_vcpu_precreate); > > That said, there's a flaw in my genius plan. > > 1. KVM_CREATE_VM > 2. KVM_CAP_MAX_VCPU_ID, set max_vcpu_ids=1 > 3. KVM_CREATE_VCPU, create IPIv table but ultimately fails > 4. KVM decrements created_vcpus back to '0' > 5. KVM_CAP_MAX_VCPU_ID, set max_vcpu_ids=4096 > 6. KVM_CREATE_VCPU w/ ID out of range > > In other words, malicious userspace could trigger buffer overflow. This is the tricky exploit that make max_vcpu_ids update more times. I think we can avoid this issue by checking pid table availability during the pre-creation of the first vCPU. If it's already allocated, free it and re-allocate to accommodate table size to new max_vcpu_ids if updated. > That could be solved by adding an arch hook to undo precreate, but that's gross > and a good indication that we're trying to solve this the wrong way. > > I think it's high time we add KVM_FINALIZE_VM, though that's probably a bad name > since e.g. TDX wants to use that name for VM really, really, being finalized[*], > i.e. after all vCPUs have been created. > > KVM_POST_CREATE_VM? That's not very good either. > > Paolo or anyone else, thoughts? > > [*] https://lore.kernel.org/all/83768bf0f786d24f49d9b698a45ba65441ef5ef0.1646422845.git.isaku.yamahata@intel.com