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 15CA8C433FE for ; Thu, 21 Apr 2022 18:33:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4F50C6B0072; Thu, 21 Apr 2022 14:33:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4A4076B0073; Thu, 21 Apr 2022 14:33:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 36C2D6B0074; Thu, 21 Apr 2022 14:33:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.25]) by kanga.kvack.org (Postfix) with ESMTP id 27B4C6B0072 for ; Thu, 21 Apr 2022 14:33:15 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id D65E23804 for ; Thu, 21 Apr 2022 18:33:14 +0000 (UTC) X-FDA: 79381733508.20.016D4BB Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf23.hostedemail.com (Postfix) with ESMTP id BB70014002A for ; Thu, 21 Apr 2022 18:33:11 +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 3C5DB60B38; Thu, 21 Apr 2022 18:33:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3B3E6C385A9; Thu, 21 Apr 2022 18:33:09 +0000 (UTC) Date: Thu, 21 Apr 2022 19:33:05 +0100 From: Catalin Marinas To: Kees Cook Cc: Topi Miettinen , Andrew Morton , Christoph Hellwig , Lennart Poettering , Zbigniew =?utf-8?Q?J=C4=99drzejewski-Szmek?= , Will Deacon , Alexander Viro , Eric Biederman , Szabolcs Nagy , Mark Brown , Jeremy Linton , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-abi-devel@lists.sourceforge.net, linux-hardening@vger.kernel.org, Jann Horn , Salvatore Mesoraca , Igor Zhbanov Subject: Re: [PATCH RFC 0/4] mm, arm64: In-kernel support for memory-deny-write-execute (MDWE) Message-ID: References: <20220413134946.2732468-1-catalin.marinas@arm.com> <202204141028.0482B08@keescook> <202204201610.093C9D5FE8@keescook> <202204210941.4318DE6E8@keescook> <202204211030.B0093CC14@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202204211030.B0093CC14@keescook> Authentication-Results: imf23.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none); spf=pass (imf23.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: rspam12 X-Rspamd-Queue-Id: BB70014002A X-Stat-Signature: hm38qbs3uwx93wf5oxcgr7iq6f151hs9 X-HE-Tag: 1650565991-392353 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 Thu, Apr 21, 2022 at 10:41:43AM -0700, Kees Cook wrote: > On Thu, Apr 21, 2022 at 06:24:21PM +0100, Catalin Marinas wrote: > > On Thu, Apr 21, 2022 at 09:42:23AM -0700, Kees Cook wrote: > > > On Thu, Apr 21, 2022 at 04:35:15PM +0100, Catalin Marinas wrote: > > > > Do we want the "was PROT_WRITE" or we just reject mprotect(PROT_EXEC) if > > > > the vma is not already PROT_EXEC? The latter is closer to the current > > > > systemd approach. The former allows an mprotect(PROT_EXEC) if the > > > > mapping was PROT_READ only for example. > > > > > > > > I'd drop the "was PROT_WRITE" for now if the aim is a drop-in > > > > replacement for BPF MDWE. > > > > > > I think "was PROT_WRITE" is an important part of the defense that > > > couldn't be done with a simple seccomp filter (which is why the filter > > > ended up being a problem in the first place). > > > > I would say "was PROT_WRITE" is slightly more relaxed than "is not > > already PROT_EXEC". The seccomp filter can't do "is not already > > PROT_EXEC" either since it only checks the mprotect() arguments, not the > > current vma flags. > > > > So we have (with sub-cases): > > > > 1. Current BPF filter: > > > > a) mmap(PROT_READ|PROT_WRITE|PROT_EXEC); // fails > > > > b) mmap(PROT_READ|PROT_EXEC); > > mprotect(PROT_READ|PROT_EXEC|PROT_BTI); // fails > > > > c) mmap(PROT_READ); > > mprotect(PROT_READ|PROT_EXEC); // fails > > > > d) mmap(PROT_READ|PROT_WRITE); > > mprotect(PROT_READ); > > mprotect(PROT_READ|PROT_EXEC); // fails > > > > 2. "is not already PROT_EXEC": > > > > a) mmap(PROT_READ|PROT_WRITE|PROT_EXEC); // fails > > > > b) mmap(PROT_READ|PROT_EXEC); > > mprotect(PROT_READ|PROT_EXEC|PROT_BTI); // passes > > > > c) mmap(PROT_READ); > > mprotect(PROT_READ|PROT_EXEC); // fails > > > > d) mmap(PROT_READ|PROT_WRITE); > > mprotect(PROT_READ); > > mprotect(PROT_READ|PROT_EXEC); // fails > > > > 3. "is or was not PROT_WRITE": > > > > a) mmap(PROT_READ|PROT_WRITE|PROT_EXEC); // fails > > > > b) mmap(PROT_READ|PROT_EXEC); > > mprotect(PROT_READ|PROT_EXEC|PROT_BTI); // passes > > > > c) mmap(PROT_READ); > > mprotect(PROT_READ|PROT_EXEC); // passes > > > > d) mmap(PROT_READ|PROT_WRITE); > > mprotect(PROT_READ); > > mprotect(PROT_READ|PROT_EXEC); // fails > > [edited above to show each case] Thanks, I was in a rush to get home ;). > restated what was already summarized: > Problem is 1.b. 2 and 3 solve it. 3 is more relaxed (c passes). > > > If we don't care about 3.c, we might as well go for (2). I don't mind, > > already went for (3) in this series. I think either of them would not be > > a regression on MDWE, unless there is some test that attempts 3.c and > > expects it to fail. > > I should stop arguing for a less restrictive mode. ;) It just feels weird > that the combinations are API-mediated, rather than logically defined: > I can do PROT_READ|PROT_EXEC with mmap but not mprotect under 2. As > opposed to saying "the vma cannot be executable if it is or ever was > writable". I find the latter much easier to reason about as far as the > expectations of system state. I had the same reasoning, hence option 3 in this series. I prefer to treat mmap(PROT_READ|PROT_EXEC) and mprotect(PROT_READ|PROT_EXEC) in a similar way. -- Catalin