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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 E6409C04AAF for ; Thu, 16 May 2019 14:16:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C1A2120862 for ; Thu, 16 May 2019 14:16:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727138AbfEPOQp (ORCPT ); Thu, 16 May 2019 10:16:45 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:47304 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726696AbfEPOQp (ORCPT ); Thu, 16 May 2019 10:16:45 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CEBF31715; Thu, 16 May 2019 07:16:44 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 782F93F71E; Thu, 16 May 2019 07:16:43 -0700 (PDT) Date: Thu, 16 May 2019 15:16:41 +0100 From: Mark Rutland To: Steven Price Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, Mike Rapoport , Andrew Morton , Will Deacon , Catalin Marinas Subject: Re: Bad virt_to_phys since commit 54c7a8916a887f35 Message-ID: <20190516141640.GC43059@lakrids.cambridge.arm.com> References: <20190516133820.GA43059@lakrids.cambridge.arm.com> <20190516134105.GB43059@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 16, 2019 at 03:05:31PM +0100, Steven Price wrote: > On 16/05/2019 14:41, Mark Rutland wrote: > > On Thu, May 16, 2019 at 02:38:20PM +0100, Mark Rutland wrote: > >> Hi, > >> > >> Since commit: > >> > >> 54c7a8916a887f35 ("initramfs: free initrd memory if opening /initrd.image fails") > > > > Ugh, I dropped a paragarph here. > > > > Since that commit, I'm seeing a boot-time splat on arm64 when using > > CONFIG_DEBUG_VIRTUAL. I'm running an arm64 syzkaller instance, and this > > kills the VM, preventing further testing, which is unfortunate. > > > > Mark. > > > >> IIUC prior to that commit, we'd only attempt to free an intird if we had > >> one, whereas now we do so unconditionally. AFAICT, in this case > >> initrd_start has not been initialized (I'm not using an initrd or > >> initramfs on my system), so we end up trying virt_to_phys() on a bogus > >> VA in free_initrd_mem(). > >> > >> Any ideas on the right way to fix this? > > Your analysis looks right to me. In my review I'd managed to spot the > change in behaviour when CONFIG_INITRAMFS_FORCE is set (the initrd is > freed), but I'd overlooked what happens if initrd_start == 0 (the > non-existent initrd is attempted to be freed). > > I suspect the following is sufficient to fix the problem: > > ----8<----- > diff --git a/init/initramfs.c b/init/initramfs.c > index 435a428c2af1..178130fd61c2 100644 > --- a/init/initramfs.c > +++ b/init/initramfs.c > @@ -669,7 +669,7 @@ static int __init populate_rootfs(void) > * If the initrd region is overlapped with crashkernel reserved region, > * free only memory that is not part of crashkernel region. > */ > - if (!do_retain_initrd && !kexec_free_initrd()) > + if (!do_retain_initrd && initrd_start && !kexec_free_initrd()) > free_initrd_mem(initrd_start, initrd_end); > initrd_start = 0; > initrd_end = 0; That works for me. If you spin this as a real patch: Tested-by: Mark Rutland As I mentioned, initrd_start has not been initialized at all, so I suspect we should also update its declaration in init/do_mounts_initrd.c such that it is guaranteed to be initialized to zero. We get away with that today, but that won't necessarily hold with LTO and so on... Thanks, Mark.