From patchwork Fri Nov 22 16:58:18 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 11258171 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 8FC1B109A for ; Fri, 22 Nov 2019 16:58:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A0922071F for ; Fri, 22 Nov 2019 16:58:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726784AbfKVQ6U (ORCPT ); Fri, 22 Nov 2019 11:58:20 -0500 Received: from mga07.intel.com ([134.134.136.100]:51805 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726620AbfKVQ6U (ORCPT ); Fri, 22 Nov 2019 11:58:20 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 22 Nov 2019 08:58:19 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,230,1571727600"; d="scan'208";a="201580258" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.41]) by orsmga008.jf.intel.com with ESMTP; 22 Nov 2019 08:58:19 -0800 From: Sean Christopherson To: Paolo Bonzini , =?utf-8?b?UmFkaW0gS3LEjW3DocWZ?= Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] KVM: x86: Grab KVM's srcu lock when setting nested state Date: Fri, 22 Nov 2019 08:58:18 -0800 Message-Id: <20191122165818.32558-1-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.24.0 MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Acquire kvm->srcu for the duration of ->set_nested_state() to fix a bug where nVMX derefences ->memslots without holding ->srcu or ->slots_lock. The other half of nested migration, ->get_nested_state(), does not need to acquire ->srcu as it is a purely a dump of internal KVM (and CPU) state to userspace. Detected as an RCU lockdep splat that is 100% reproducible by running KVM's state_test selftest with CONFIG_PROVE_LOCKING=y. Note that the failing function, kvm_is_visible_gfn(), is only checking the validity of a gfn, it's not actually accessing guest memory (which is more or less unsupported during vmx_set_nested_state() due to incorrect MMU state), i.e. vmx_set_nested_state() itself isn't fundamentally broken. In any case, setting nested state isn't a fast path so there's no reason to go out of our way to avoid taking ->srcu. ============================= WARNING: suspicious RCU usage 5.4.0-rc7+ #94 Not tainted ----------------------------- include/linux/kvm_host.h:626 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 1 lock held by evmcs_test/10939: #0: ffff88826ffcb800 (&vcpu->mutex){+.+.}, at: kvm_vcpu_ioctl+0x85/0x630 [kvm] stack backtrace: CPU: 1 PID: 10939 Comm: evmcs_test Not tainted 5.4.0-rc7+ #94 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: dump_stack+0x68/0x9b kvm_is_visible_gfn+0x179/0x180 [kvm] mmu_check_root+0x11/0x30 [kvm] fast_cr3_switch+0x40/0x120 [kvm] kvm_mmu_new_cr3+0x34/0x60 [kvm] nested_vmx_load_cr3+0xbd/0x1f0 [kvm_intel] nested_vmx_enter_non_root_mode+0xab8/0x1d60 [kvm_intel] vmx_set_nested_state+0x256/0x340 [kvm_intel] kvm_arch_vcpu_ioctl+0x491/0x11a0 [kvm] kvm_vcpu_ioctl+0xde/0x630 [kvm] do_vfs_ioctl+0xa2/0x6c0 ksys_ioctl+0x66/0x70 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x54/0x200 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7f59a2b95f47 Fixes: 8fcc4b5923af5 ("kvm: nVMX: Introduce KVM_CAP_NESTED_STATE") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 5d530521f11d..656878a9802e 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4421,6 +4421,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp, case KVM_SET_NESTED_STATE: { struct kvm_nested_state __user *user_kvm_nested_state = argp; struct kvm_nested_state kvm_state; + int idx; r = -EINVAL; if (!kvm_x86_ops->set_nested_state) @@ -4444,7 +4445,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp, && !(kvm_state.flags & KVM_STATE_NESTED_GUEST_MODE)) break; + idx = srcu_read_lock(&vcpu->kvm->srcu); r = kvm_x86_ops->set_nested_state(vcpu, user_kvm_nested_state, &kvm_state); + srcu_read_unlock(&vcpu->kvm->srcu, idx); break; } case KVM_GET_SUPPORTED_HV_CPUID: {