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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 78D5BC54FCE for ; Mon, 23 Mar 2020 16:39:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5392420722 for ; Mon, 23 Mar 2020 16:39:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727650AbgCWQj1 (ORCPT ); Mon, 23 Mar 2020 12:39:27 -0400 Received: from mga09.intel.com ([134.134.136.24]:20398 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727479AbgCWQj1 (ORCPT ); Mon, 23 Mar 2020 12:39:27 -0400 IronPort-SDR: YQD3g7pZTFbkZtaxU6+O1FOEqGnvMkziwgZwnUpar6yJxQ4Q2eWUhG2KxxHnYainQmqfdLGsfV fnBhqoUQrfUg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Mar 2020 09:39:26 -0700 IronPort-SDR: CbB0ngl3XhoDgFa+je1ygSyt/uHRvif4A2KEUIoYhgEeWnTyYSiYMqs3zRyRyuhEtk4MF8sbae 3iVvhMFf35uw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,297,1580803200"; d="scan'208";a="419559426" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga005.jf.intel.com with ESMTP; 23 Mar 2020 09:39:25 -0700 Date: Mon, 23 Mar 2020 09:39:25 -0700 From: Sean Christopherson To: Alexander Potapenko Cc: Paolo Bonzini , Dmitry Vyukov , syzbot , clang-built-linux , Borislav Petkov , "H. Peter Anvin" , Jim Mattson , Joerg Roedel , KVM list , LKML , Ingo Molnar , syzkaller-bugs , Thomas Gleixner , Vitaly Kuznetsov , wanpengli@tencent.com, the arch/x86 maintainers Subject: Re: BUG: unable to handle kernel NULL pointer dereference in handle_external_interrupt_irqoff Message-ID: <20200323163925.GP28711@linux.intel.com> References: <000000000000277a0405a16bd5c9@google.com> <5058aabe-f32d-b8ef-57ed-f9c0206304c5@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 23, 2020 at 05:31:15PM +0100, Alexander Potapenko wrote: > On Mon, Mar 23, 2020 at 9:18 AM Paolo Bonzini wrote: > > > > On 22/03/20 07:59, Dmitry Vyukov wrote: > > > > > > The commit range is presumably > > > fb279f4e238617417b132a550f24c1e86d922558..63849c8f410717eb2e6662f3953ff674727303e7 > > > But I don't see anything that says "it's me". The only commit that > > > does non-trivial changes to x86/vmx seems to be "KVM: VMX: check > > > descriptor table exits on instruction emulation": > > > > That seems unlikely, it's a completely different file and it would only > > affect the outside (non-nested) environment rather than your own kernel. > > > > The only instance of "0x86" in the registers is in the flags: > > > > > RSP: 0018:ffffc90001ac7998 EFLAGS: 00010086 > > > RAX: ffffc90001ac79c8 RBX: fffffe0000000000 RCX: 0000000000040000 > > > RDX: ffffc9000e20f000 RSI: 000000000000b452 RDI: 000000000000b453 > > > RBP: 0000000000000ec0 R08: ffffffff83987523 R09: ffffffff811c7eca > > > R10: ffff8880a4e94200 R11: 0000000000000002 R12: dffffc0000000000 > > > R13: fffffe0000000ec8 R14: ffffffff880016f0 R15: fffffe0000000ecb > > > FS: 00007fb50e370700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000 > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > CR2: 000000000000005c CR3: 0000000092fc7000 CR4: 00000000001426f0 > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > > > That would suggest a miscompilation of the inline assembly, which does > > push the flags: > > > > #ifdef CONFIG_X86_64 > > "mov %%" _ASM_SP ", %[sp]\n\t" > > "and $0xfffffffffffffff0, %%" _ASM_SP "\n\t" > > "push $%c[ss]\n\t" > > "push %[sp]\n\t" > > #endif > > "pushf\n\t" > > __ASM_SIZE(push) " $%c[cs]\n\t" > > CALL_NOSPEC > > > > > > It would not explain why it suddenly started to break, unless the clang > > version also changed, but it would be easy to ascertain and fix (in > > either KVM or clang). Dmitry, can you send me the vmx.o and > > kvm-intel.ko files? > > On a quick glance, Clang does not miscompile this part. Clang definitely miscompiles the asm, the indirect call operates on the EFLAGS value, not on @entry as expected. It looks like clang doesn't honor ASM_CALL_CONSTRAINT, which effectively tells the compiler that %rsp is getting clobbered, e.g. the "mov %r14,0x8(%rsp)" is loading @entry for "callq *0x8(%rsp)", which breaks because of asm's pushes. clang: kvm_before_interrupt(vcpu); asm volatile( ffffffff811b798e: 4c 89 74 24 08 mov %r14,0x8(%rsp) ffffffff811b7993: 48 89 e0 mov %rsp,%rax ffffffff811b7996: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp ffffffff811b799a: 6a 18 pushq $0x18 ffffffff811b799c: 50 push %rax ffffffff811b799d: 9c pushfq ffffffff811b799e: 6a 10 pushq $0x10 ffffffff811b79a0: ff 54 24 08 callq *0x8(%rsp) <--------- calls the EFLAGS value kvm_after_interrupt(): gcc: kvm_before_interrupt(vcpu); asm volatile( ffffffff8118e17c: 48 89 e0 mov %rsp,%rax ffffffff8118e17f: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp ffffffff8118e183: 6a 18 pushq $0x18 ffffffff8118e185: 50 push %rax ffffffff8118e186: 9c pushfq ffffffff8118e187: 6a 10 pushq $0x10 ffffffff8118e189: ff d3 callq *%rbx <-------- calls @entry kvm_after_interrupt():