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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 5A83DC4360C for ; Wed, 2 Oct 2019 21:46:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F6A421A4C for ; Wed, 2 Oct 2019 21:46:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570052761; bh=O7NvbZugYvMLZ/+OzzjuvSo6dEQ9WQ3OuCN4ONY0600=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=wGqqbyKfK76oNAtl5c2jxd1eTLkqZzWASSUgXesn7ttLI7JglIZfj2QX+uc8j12LD TuJIw3yJHjAicfl1r18y5z2RWOlCSnqBA5hvU5nSfZdr471rT4wVUEGQ9x+mhpS4GO RNuaIfywiCH6W/NEPNRGKbpL/78kKu2qBrJiu6lY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728201AbfJBVqA (ORCPT ); Wed, 2 Oct 2019 17:46:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:44128 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727832AbfJBVqA (ORCPT ); Wed, 2 Oct 2019 17:46:00 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) (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 D25B7217D7; Wed, 2 Oct 2019 21:45:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570052759; bh=O7NvbZugYvMLZ/+OzzjuvSo6dEQ9WQ3OuCN4ONY0600=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=IoJhq4Pv0UhAVg1ket7V7IvKUNoWBUnQpaVqvxZCay/k28RCXEZQxTzXpCbrPbPME cgkeE7CWmXA8qmksbohVGhqJPnTg7I3v9HBgfbHffqP5+Ygdrbzc8YDtX+LZlPMol+ KmZyg78A51sNcAs9ORccMZAsCuWoBGBtM3/Z25FY= Date: Wed, 2 Oct 2019 14:45:58 -0700 From: Andrew Morton To: Will Deacon Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, contact@xogium.me, Russell King , Greg Kroah-Hartman , Ingo Molnar , Kees Cook , stable@vger.kernel.org Subject: Re: [PATCH] panic: Ensure preemption is disabled during panic() Message-Id: <20191002144558.87531ea9f68b535453fedd3e@linux-foundation.org> In-Reply-To: <20191002123538.22609-1-will@kernel.org> References: <20191002123538.22609-1-will@kernel.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2 Oct 2019 13:35:38 +0100 Will Deacon wrote: > 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. > > ... > > --- a/kernel/panic.c > +++ b/kernel/panic.c > @@ -180,6 +180,7 @@ void panic(const char *fmt, ...) > * after setting panic_cpu) from invoking panic() again. > */ > local_irq_disable(); > + preempt_disable_notrace(); > > /* > * It's possible to come here directly from a panic-assertion and We still do a lot of stuff (kexec, kgdb, etc) after this preempt_disable() and I worry that something in there will now trigger a might_sleep() warning as a result?