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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham 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 54B7CC352AA for ; Tue, 1 Oct 2019 20:50:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2F263215EA for ; Tue, 1 Oct 2019 20:50:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727404AbfJAUuZ (ORCPT ); Tue, 1 Oct 2019 16:50:25 -0400 Received: from mga02.intel.com ([134.134.136.20]:27912 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726436AbfJAUuZ (ORCPT ); Tue, 1 Oct 2019 16:50:25 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 01 Oct 2019 13:50:24 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,571,1559545200"; d="scan'208";a="197979063" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.41]) by FMSMGA003.fm.intel.com with ESMTP; 01 Oct 2019 13:50:24 -0700 From: Sean Christopherson To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org Cc: "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: [PATCH] x86/apic/x2apic: Fix a NULL pointer deref when handling a dying cpu Date: Tue, 1 Oct 2019 13:50:19 -0700 Message-Id: <20191001205019.5789-1-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.22.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Check that the per-cpu cluster mask pointer has been set prior to clearing a dying cpu's bit. The per-cpu pointer is not set until the target cpu reaches smp_callin() during CPUHP_BRINGUP_CPU, whereas the teardown function, x2apic_dead_cpu(), is associated with the earlier CPUHP_X2APIC_PREPARE. If an error occurs before the cpu is awakened, e.g. if do_boot_cpu() itself fails, x2apic_dead_cpu() will dereference the NULL pointer and cause a panic. smpboot: do_boot_cpu failed(-22) to wakeup CPU#1 BUG: kernel NULL pointer dereference, address: 0000000000000008 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP PTI CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.2.0+ #120 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:x2apic_dead_cpu+0x1a/0x30 Code: 48 0f b3 78 08 31 c0 c3 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 RSP: 0000:ffffc9000001be58 EFLAGS: 00010286 RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000 RDX: ffff88817bb00000 RSI: 0000000000000027 RDI: 0000000000000001 RBP: 0000000000000027 R08: 0000000000000000 R09: 0000000000000001 R10: 0000000000000266 R11: 0000000000000002 R12: 0000000000000000 R13: ffffffff81038c00 R14: 00000000fffffffb R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff88817ba00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000008 CR3: 000000000500a001 CR4: 0000000000160ef0 Call Trace: cpuhp_invoke_callback+0x9a/0x580 _cpu_up+0x10d/0x140 do_cpu_up+0x69/0xb0 smp_init+0x63/0xa9 kernel_init_freeable+0xd7/0x229 ? rest_init+0xa0/0xa0 kernel_init+0xa/0x100 ret_from_fork+0x35/0x40 Fixes: 023a611748fd5 ("x86/apic/x2apic: Simplify cluster management") Cc: stable@vger.kernel.org Cc: Thomas Gleixner Signed-off-by: Sean Christopherson --- The do_boot_cpu() -EINVAL failure is due to unrelated code that isn't in mainline, i.e. there is no underlying bug that needs to be investigated. arch/x86/kernel/apic/x2apic_cluster.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c index 45e92cba92f5..b0889c48a2ac 100644 --- a/arch/x86/kernel/apic/x2apic_cluster.c +++ b/arch/x86/kernel/apic/x2apic_cluster.c @@ -156,7 +156,8 @@ static int x2apic_dead_cpu(unsigned int dead_cpu) { struct cluster_mask *cmsk = per_cpu(cluster_masks, dead_cpu); - cpumask_clear_cpu(dead_cpu, &cmsk->mask); + if (cmsk) + cpumask_clear_cpu(dead_cpu, &cmsk->mask); free_cpumask_var(per_cpu(ipi_mask, dead_cpu)); return 0; } -- 2.22.0