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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 99C51C4332F for ; Fri, 22 Apr 2022 13:12:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 365136B0095; Fri, 22 Apr 2022 09:12:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3135D6B0096; Fri, 22 Apr 2022 09:12:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1DB2A6B0098; Fri, 22 Apr 2022 09:12:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.28]) by kanga.kvack.org (Postfix) with ESMTP id 0ED936B0095 for ; Fri, 22 Apr 2022 09:12:30 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id CDD31204B0 for ; Fri, 22 Apr 2022 13:12:29 +0000 (UTC) X-FDA: 79384554018.03.A35AA3A Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf03.hostedemail.com (Postfix) with ESMTP id 394F22000D for ; Fri, 22 Apr 2022 13:12:27 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 65AF56207A; Fri, 22 Apr 2022 13:12:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB0EBC385A8; Fri, 22 Apr 2022 13:12:24 +0000 (UTC) Date: Fri, 22 Apr 2022 14:12:21 +0100 From: Catalin Marinas To: David Hildenbrand Cc: Andrew Morton , Christoph Hellwig , Lennart Poettering , Zbigniew =?utf-8?Q?J=C4=99drzejewski-Szmek?= , Will Deacon , Alexander Viro , Eric Biederman , Kees Cook , Szabolcs Nagy , Mark Brown , Jeremy Linton , Topi Miettinen , "linux-mm@kvack.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-abi-devel@lists.sourceforge.net" Subject: Re: [PATCH RFC 2/4] mm, personality: Implement memory-deny-write-execute as a personality flag Message-ID: References: <20220413134946.2732468-1-catalin.marinas@arm.com> <20220413134946.2732468-3-catalin.marinas@arm.com> <443d978a-7092-b5b1-22f3-ae3a997080ad@redhat.com> <59401856-0e45-0ee6-1e45-667c8e00cf21@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <59401856-0e45-0ee6-1e45-667c8e00cf21@redhat.com> Authentication-Results: imf03.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none); spf=pass (imf03.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 394F22000D X-Stat-Signature: 3b55rwrxq5zni96jqy33dx1osyhn33cg X-HE-Tag: 1650633147-12629 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Apr 22, 2022 at 01:04:31PM +0200, David Hildenbrand wrote: > On 22.04.22 12:28, Catalin Marinas wrote: > > On Thu, Apr 21, 2022 at 06:37:49PM +0100, David Hildenbrand wrote: > >> Note that in the (FOLL_WRITE|FOLL_FORCE) we only require VM_MAYWRITE on > >> the vma and trigger a write fault. As the VMA is not VM_WRITE, we won't > >> actually map the PTE writable, but set it dirty. GUP will retry, find a > >> R/O pte that is dirty and where it knows that it broke COW and will > >> allow the read access, although the PTE is R/O. > >> > >> That mechanism is required to e.g., set breakpoints in R/O MAP_PRIVATE > >> kernel sections, but it's used elsewhere for page pinning as well. > >> > >> My gut feeling is that GUP(FOLL_WRITE|FOLL_FORCE) could be used right > >> now to bypass that mechanism, I might be wrong. > > > > GUP can be used to bypass this. But if an attacker can trigger such GUP > > paths via a syscall (e.g. ptrace(PTRACE_POKEDATA)), I think we need the > > checks on those paths (and reject the syscall) rather than on > > mmap/mprotect(). This would be covered by something like CAP_SYS_PTRACE. > > I was told that RDMA uses FOLL_FORCE|FOLL_WRITE and is available to > unprivileged users. Ah, do they really need this? At a quick search, ib_umem_get() for example: unsigned int gup_flags = FOLL_WRITE; ... if (!umem->writable) gup_flags |= FOLL_FORCE; I guess with a new MDWE flag we can make the GUP code ignore FOLL_FORCE if VM_EXEC. -- Catalin