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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 E8914FA3728 for ; Wed, 16 Oct 2019 21:53:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD68121D7A for ; Wed, 16 Oct 2019 21:53:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571262792; bh=hNYIw7BePq0zXre+xmi6ULiuwQlpVyI6psPdkO41fes=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=DEiHrNe2Lzv9H8AhLx5C9cZDYRWVSuWyqMXy3JViTH0lGADRS6yVDBDou4jcy2VTx B0LapAAVen77OQZXljFZyo9x6vszTR3//BZPalylN4Vmx665aRJg5DM6PL1jHSIrxy XVwWbUw9ZF2LU+SQJO3i/J3FoIsO7HvxWe4T7buk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437337AbfJPVxL (ORCPT ); Wed, 16 Oct 2019 17:53:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:41752 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394828AbfJPVxI (ORCPT ); Wed, 16 Oct 2019 17:53:08 -0400 Received: from localhost (unknown [192.55.54.58]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 18E1520872; Wed, 16 Oct 2019 21:53:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571262787; bh=hNYIw7BePq0zXre+xmi6ULiuwQlpVyI6psPdkO41fes=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vbkm/avg6TosfxcmQZQhA2hfwwrNcc4TySCUxIg6140GNmxwh8CnNeLMzN2w5R8Z+ /bNZnivjVjXBoZxxvABdgjo5nDPIpFf2+ZG11EaqXyHQ9c9RCK6Kyyj1Dcj4shXoSH Ct/xDv6bUqgeX08SjZxEGbrpf0W+q7V6KvvNGV58= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Will Deacon , Xogium , Kees Cook , Russell King , Ingo Molnar , Petr Mladek , Feng Tang , Andrew Morton , Linus Torvalds Subject: [PATCH 4.4 28/79] panic: ensure preemption is disabled during panic() Date: Wed, 16 Oct 2019 14:50:03 -0700 Message-Id: <20191016214755.396779680@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191016214729.758892904@linuxfoundation.org> References: <20191016214729.758892904@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Will Deacon commit 20bb759a66be52cf4a9ddd17fddaf509e11490cd upstream. Calling 'panic()' on a kernel with CONFIG_PREEMPT=y can leave the calling CPU in an infinite loop, but with interrupts and preemption enabled. From this state, userspace can continue to be scheduled, despite the system being "dead" as far as the kernel is concerned. This is easily reproducible on arm64 when booting with "nosmp" on the command line; a couple of shell scripts print out a periodic "Ping" message whilst another triggers a crash by writing to /proc/sysrq-trigger: | sysrq: Trigger a crash | Kernel panic - not syncing: sysrq triggered crash | CPU: 0 PID: 1 Comm: init Not tainted 5.2.15 #1 | Hardware name: linux,dummy-virt (DT) | Call trace: | dump_backtrace+0x0/0x148 | show_stack+0x14/0x20 | dump_stack+0xa0/0xc4 | panic+0x140/0x32c | sysrq_handle_reboot+0x0/0x20 | __handle_sysrq+0x124/0x190 | write_sysrq_trigger+0x64/0x88 | proc_reg_write+0x60/0xa8 | __vfs_write+0x18/0x40 | vfs_write+0xa4/0x1b8 | ksys_write+0x64/0xf0 | __arm64_sys_write+0x14/0x20 | el0_svc_common.constprop.0+0xb0/0x168 | el0_svc_handler+0x28/0x78 | el0_svc+0x8/0xc | Kernel Offset: disabled | CPU features: 0x0002,24002004 | Memory Limit: none | ---[ end Kernel panic - not syncing: sysrq triggered crash ]--- | Ping 2! | Ping 1! | Ping 1! | Ping 2! The issue can also be triggered on x86 kernels if CONFIG_SMP=n, otherwise local interrupts are disabled in 'smp_send_stop()'. Disable preemption in 'panic()' before re-enabling interrupts. Link: http://lkml.kernel.org/r/20191002123538.22609-1-will@kernel.org Link: https://lore.kernel.org/r/BX1W47JXPMR8.58IYW53H6M5N@dragonstone Signed-off-by: Will Deacon Reported-by: Xogium Reviewed-by: Kees Cook Cc: Russell King Cc: Greg Kroah-Hartman Cc: Ingo Molnar Cc: Petr Mladek Cc: Feng Tang Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/panic.c | 1 + 1 file changed, 1 insertion(+) --- a/kernel/panic.c +++ b/kernel/panic.c @@ -84,6 +84,7 @@ void panic(const char *fmt, ...) * after the panic_lock is acquired) from invoking panic again. */ local_irq_disable(); + preempt_disable_notrace(); /* * It's possible to come here directly from a panic-assertion and