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=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 38C6DC433B4 for ; Wed, 14 Apr 2021 12:20:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 17B186105A for ; Wed, 14 Apr 2021 12:20:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350778AbhDNMVS (ORCPT ); Wed, 14 Apr 2021 08:21:18 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:52923 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346904AbhDNMVM (ORCPT ); Wed, 14 Apr 2021 08:21:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618402850; h=from:from: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=NO4FGUOTnvyNv6ZEsf7CqScF3ifaTTajd0Qf2emlRl0=; b=YpS1w1cuS3xQcpeGuRymmMxzhteusWRnHMQGAS8iquKnbbXZ3mpk7McTt+ojglvvSVusfz eqLzd9ip+oUcSHiFaTD3/iE98RBgPqnSWBCWFF1XNSMPgyTctMqnHA05N/4OcFL5mzZqbm 8ZxxW6ybr1XpNXFFceGsu0tj9EY8tJw= 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-424-MbvmUyxeMQSe91Bt0GGgJQ-1; Wed, 14 Apr 2021 08:20:46 -0400 X-MC-Unique: MbvmUyxeMQSe91Bt0GGgJQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 03C101006C81; Wed, 14 Apr 2021 12:20:44 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-112-148.ams2.redhat.com [10.36.112.148]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 571D210016FE; Wed, 14 Apr 2021 12:20:34 +0000 (UTC) From: Florian Weimer To: Jann Horn Cc: Andrei Vagin , kernel list , Linux API , linux-um@lists.infradead.org, criu@openvz.org, Andrei Vagin , Andrew Morton , Andy Lutomirski , Anton Ivanov , Christian Brauner , Dmitry Safonov <0x7f454c46@gmail.com>, Ingo Molnar , Jeff Dike , Mike Rapoport , Michael Kerrisk , Oleg Nesterov , Peter Zijlstra , Richard Weinberger , Thomas Gleixner Subject: Re: [PATCH 0/4 POC] Allow executing code and syscalls in another address space References: <20210414055217.543246-1-avagin@gmail.com> <87blahb1pr.fsf@oldenburg.str.redhat.com> Date: Wed, 14 Apr 2021 14:20:48 +0200 In-Reply-To: (Jann Horn's message of "Wed, 14 Apr 2021 13:24:30 +0200") Message-ID: <874kg99hwf.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Jann Horn: > On Wed, Apr 14, 2021 at 12:27 PM Florian Weimer wrot= e: >> >> * Andrei Vagin: >> >> > We already have process_vm_readv and process_vm_writev to read and wri= te >> > to a process memory faster than we can do this with ptrace. And now it >> > is time for process_vm_exec that allows executing code in an address >> > space of another process. We can do this with ptrace but it is much >> > slower. >> > >> > =3D Use-cases =3D >> >> We also have some vaguely related within the same address space: running >> code on another thread, without modifying its stack, while it has signal >> handlers blocked, and without causing system calls to fail with EINTR. >> This can be used to implement certain kinds of memory barriers. > > That's what the membarrier() syscall is for, right? Unless you don't > want to register all threads for expedited membarrier use? membarrier is not sufficiently powerful for revoking biased locks, for example. For the EINTR issue, is an example. I believe CIFS has since seen a few fixes (after someone reported that tar on CIFS wouldn't work because the SIGCHLD causing utimensat to fail=E2=80=94and there isn't even a signal handler for SIGCHLD= !), but the time it took to get to this point doesn't give me confidence that it is safe to send signals to a thread that is running unknown code. But as you explained regarding the set*id broadcast, it seems that if we had this run-on-another-thread functionality, we would likely encounter issues similar to those with SA_RESTART. We don't see the issue with set*id today because it's a rare operation, and multi-threaded file servers that need to change credentials frequently opt out of the set*id broadcast anyway. (What I have in mind is a future world where any printf call, any malloc call, can trigger such a broadcast.) The cross-VM CRIU scenario would probably somewhere in between (not quite the printf/malloc level, but more frequent than set*id). Thanks, Florian From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lWeVo-007kKH-0H for linux-um@lists.infradead.org; Wed, 14 Apr 2021 12:20:53 +0000 From: Florian Weimer Subject: Re: [PATCH 0/4 POC] Allow executing code and syscalls in another address space References: <20210414055217.543246-1-avagin@gmail.com> <87blahb1pr.fsf@oldenburg.str.redhat.com> Date: Wed, 14 Apr 2021 14:20:48 +0200 In-Reply-To: (Jann Horn's message of "Wed, 14 Apr 2021 13:24:30 +0200") Message-ID: <874kg99hwf.fsf@oldenburg.str.redhat.com> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Jann Horn Cc: Andrei Vagin , kernel list , Linux API , linux-um@lists.infradead.org, criu@openvz.org, Andrei Vagin , Andrew Morton , Andy Lutomirski , Anton Ivanov , Christian Brauner , Dmitry Safonov <0x7f454c46@gmail.com>, Ingo Molnar , Jeff Dike , Mike Rapoport , Michael Kerrisk , Oleg Nesterov , Peter Zijlstra , Richard Weinberger , Thomas Gleixner KiBKYW5uIEhvcm46Cgo+IE9uIFdlZCwgQXByIDE0LCAyMDIxIGF0IDEyOjI3IFBNIEZsb3JpYW4g V2VpbWVyIDxmd2VpbWVyQHJlZGhhdC5jb20+IHdyb3RlOgo+Pgo+PiAqIEFuZHJlaSBWYWdpbjoK Pj4KPj4gPiBXZSBhbHJlYWR5IGhhdmUgcHJvY2Vzc192bV9yZWFkdiBhbmQgcHJvY2Vzc192bV93 cml0ZXYgdG8gcmVhZCBhbmQgd3JpdGUKPj4gPiB0byBhIHByb2Nlc3MgbWVtb3J5IGZhc3RlciB0 aGFuIHdlIGNhbiBkbyB0aGlzIHdpdGggcHRyYWNlLiBBbmQgbm93IGl0Cj4+ID4gaXMgdGltZSBm b3IgcHJvY2Vzc192bV9leGVjIHRoYXQgYWxsb3dzIGV4ZWN1dGluZyBjb2RlIGluIGFuIGFkZHJl c3MKPj4gPiBzcGFjZSBvZiBhbm90aGVyIHByb2Nlc3MuIFdlIGNhbiBkbyB0aGlzIHdpdGggcHRy YWNlIGJ1dCBpdCBpcyBtdWNoCj4+ID4gc2xvd2VyLgo+PiA+Cj4+ID4gPSBVc2UtY2FzZXMgPQo+ Pgo+PiBXZSBhbHNvIGhhdmUgc29tZSB2YWd1ZWx5IHJlbGF0ZWQgd2l0aGluIHRoZSBzYW1lIGFk ZHJlc3Mgc3BhY2U6IHJ1bm5pbmcKPj4gY29kZSBvbiBhbm90aGVyIHRocmVhZCwgd2l0aG91dCBt b2RpZnlpbmcgaXRzIHN0YWNrLCB3aGlsZSBpdCBoYXMgc2lnbmFsCj4+IGhhbmRsZXJzIGJsb2Nr ZWQsIGFuZCB3aXRob3V0IGNhdXNpbmcgc3lzdGVtIGNhbGxzIHRvIGZhaWwgd2l0aCBFSU5UUi4K Pj4gVGhpcyBjYW4gYmUgdXNlZCB0byBpbXBsZW1lbnQgY2VydGFpbiBraW5kcyBvZiBtZW1vcnkg YmFycmllcnMuCj4KPiBUaGF0J3Mgd2hhdCB0aGUgbWVtYmFycmllcigpIHN5c2NhbGwgaXMgZm9y LCByaWdodD8gVW5sZXNzIHlvdSBkb24ndAo+IHdhbnQgdG8gcmVnaXN0ZXIgYWxsIHRocmVhZHMg Zm9yIGV4cGVkaXRlZCBtZW1iYXJyaWVyIHVzZT8KCm1lbWJhcnJpZXIgaXMgbm90IHN1ZmZpY2ll bnRseSBwb3dlcmZ1bCBmb3IgcmV2b2tpbmcgYmlhc2VkIGxvY2tzLCBmb3IKZXhhbXBsZS4KCkZv ciB0aGUgRUlOVFIgaXNzdWUsIDxodHRwczovL2dpdGh1Yi5jb20vZ29sYW5nL2dvL2lzc3Vlcy8z ODgzNj4gaXMgYW4KZXhhbXBsZS4gIEkgYmVsaWV2ZSBDSUZTIGhhcyBzaW5jZSBzZWVuIGEgZmV3 IGZpeGVzIChhZnRlciBzb21lb25lCnJlcG9ydGVkIHRoYXQgdGFyIG9uIENJRlMgd291bGRuJ3Qg d29yayBiZWNhdXNlIHRoZSBTSUdDSExEIGNhdXNpbmcKdXRpbWVuc2F0IHRvIGZhaWzigJRhbmQg dGhlcmUgaXNuJ3QgZXZlbiBhIHNpZ25hbCBoYW5kbGVyIGZvciBTSUdDSExEISksCmJ1dCB0aGUg dGltZSBpdCB0b29rIHRvIGdldCB0byB0aGlzIHBvaW50IGRvZXNuJ3QgZ2l2ZSBtZSBjb25maWRl bmNlCnRoYXQgaXQgaXMgc2FmZSB0byBzZW5kIHNpZ25hbHMgdG8gYSB0aHJlYWQgdGhhdCBpcyBy dW5uaW5nIHVua25vd24KY29kZS4KCkJ1dCBhcyB5b3UgZXhwbGFpbmVkIHJlZ2FyZGluZyB0aGUg c2V0KmlkIGJyb2FkY2FzdCwgaXQgc2VlbXMgdGhhdCBpZiB3ZQpoYWQgdGhpcyBydW4tb24tYW5v dGhlci10aHJlYWQgZnVuY3Rpb25hbGl0eSwgd2Ugd291bGQgbGlrZWx5IGVuY291bnRlcgppc3N1 ZXMgc2ltaWxhciB0byB0aG9zZSB3aXRoIFNBX1JFU1RBUlQuICBXZSBkb24ndCBzZWUgdGhlIGlz c3VlIHdpdGgKc2V0KmlkIHRvZGF5IGJlY2F1c2UgaXQncyBhIHJhcmUgb3BlcmF0aW9uLCBhbmQg bXVsdGktdGhyZWFkZWQgZmlsZQpzZXJ2ZXJzIHRoYXQgbmVlZCB0byBjaGFuZ2UgY3JlZGVudGlh bHMgZnJlcXVlbnRseSBvcHQgb3V0IG9mIHRoZSBzZXQqaWQKYnJvYWRjYXN0IGFueXdheS4gIChX aGF0IEkgaGF2ZSBpbiBtaW5kIGlzIGEgZnV0dXJlIHdvcmxkIHdoZXJlIGFueQpwcmludGYgY2Fs bCwgYW55IG1hbGxvYyBjYWxsLCBjYW4gdHJpZ2dlciBzdWNoIGEgYnJvYWRjYXN0LikKClRoZSBj cm9zcy1WTSBDUklVIHNjZW5hcmlvIHdvdWxkIHByb2JhYmx5IHNvbWV3aGVyZSBpbiBiZXR3ZWVu IChub3QKcXVpdGUgdGhlIHByaW50Zi9tYWxsb2MgbGV2ZWwsIGJ1dCBtb3JlIGZyZXF1ZW50IHRo YW4gc2V0KmlkKS4KClRoYW5rcywKRmxvcmlhbgoKCl9fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fCmxpbnV4LXVtIG1haWxpbmcgbGlzdApsaW51eC11bUBsaXN0 cy5pbmZyYWRlYWQub3JnCmh0dHA6Ly9saXN0cy5pbmZyYWRlYWQub3JnL21haWxtYW4vbGlzdGlu Zm8vbGludXgtdW0K