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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7B945C433EF for ; Fri, 8 Oct 2021 11:05:56 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DA19660F22 for ; Fri, 8 Oct 2021 11:05:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org DA19660F22 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:45164 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mYnhK-000800-SD for qemu-devel@archiver.kernel.org; Fri, 08 Oct 2021 07:05:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40694) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYndE-0005IA-HB for qemu-devel@nongnu.org; Fri, 08 Oct 2021 07:01:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:23053) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYnd6-0006g7-CI for qemu-devel@nongnu.org; Fri, 08 Oct 2021 07:01:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633690890; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=S3Le4MG/sH+0J17/DA3PcBuwRRGIPbf8AqLU211Mo2w=; b=b2zX06XSLR8iAMMwnvw3fplookrect98P60PmSDntFly+9UScu5UMKj7i2NeACAvLtOpVX 7lHJm7ZQUKAsfB4blmgKydrXkKQj0BXw3Q+3/3AdwyjLWOFI9hdbry4Oz+2nFi8xC/Yqef RDOh67joJ9FaKqgJJBGCLqnGDi1VHYA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-386-mIx1sSxjM12PXwYVWlgFNg-1; Fri, 08 Oct 2021 07:01:14 -0400 X-MC-Unique: mIx1sSxjM12PXwYVWlgFNg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D06CC802CB5; Fri, 8 Oct 2021 11:01:12 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5205460CCC; Fri, 8 Oct 2021 11:01:10 +0000 (UTC) Date: Fri, 8 Oct 2021 12:01:07 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Alex =?utf-8?Q?Benn=C3=A9e?= Subject: Re: Approaches for same-on-same linux-user execve? Message-ID: References: <877deoevj8.fsf@linaro.org> MIME-Version: 1.0 In-Reply-To: <877deoevj8.fsf@linaro.org> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.051, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: assad.hashmi@linaro.org, Richard Henderson , Laurent Vivier , qemu-devel@nongnu.org, James Bottomley , qemu-arm@nongnu.org, "Eric W. Biederman" , Arnd Bergmann Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Oct 07, 2021 at 03:32:19PM +0100, Alex Bennée wrote: > Hi, > > I came across a use-case this week for ARM although this may be also > applicable to architectures where QEMU's emulation is ahead of the > hardware currently widely available - for example if you want to > exercise SVE code on AArch64. When the linux-user architecture is not > the same as the host architecture then binfmt_misc works perfectly fine. > > However in the case you are running same-on-same you can't use > binfmt_misc to redirect execution to using QEMU because any attempt to > trap native binaries will cause your userspace to hang as binfmt_misc > will be invoked to run the QEMU binary needed to run your application > and a deadlock ensues. > > There are some hacks you can apply at a local level like tweaking the > elf header of the binaries you want to run under emulation and adjusting > the binfmt_mask appropriately. This works but is messy and a faff to > set-up. > > An ideal setup would be would be for the kernel to catch a SIGILL from a > failing user space program and then to re-launch the process using QEMU > with the old processes maps and execution state so it could continue. > However I suspect there are enough moving parts to make this very > fragile (e.g. what happens to the results of library feature probing > code). So two approaches I can think of are: > > Trap execve in QEMU linux-user > ------------------------------ > > We could add a flag to QEMU so at the point of execve it manually > invokes the new process with QEMU, passing on the flag to persist this > behaviour. > > > Add path mask to binfmt_misc > ---------------------------- > > The other option would be to extend binfmt_misc to have a path mask so > it only applies it's alternative execution scheme to binaries in a > particular section of the file-system (or maybe some sort of pattern?). > > Are there any other approaches you could take? Which do you think has > the most merit? Could a new Linux personality flag be useful in combination with a new flag in binfmt_misc. eg a flag "E" for binfmt_misc which indicates the rule must only be applied if the process is execve()d with PER_USE_BINFMT personality set. That would let you add a native match rule to binfmt_misc without it affecting your system initially. To then run native binaries via qemu-user you just need to set the personality() flag and the only that sub-process tree gets redirected. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|