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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A0CB1C4332F for ; Tue, 15 Nov 2022 15:37:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=NSqxAT6EGQdsx9Le3uCCVtBY2evINfCP/p/lAlmdE6M=; b=bZVm8KlcgUfAaZ WQRc85HwiXoyb1URAwMSXiStER1EuVUwElCpuMWJl7H+hPA6b5B1P0EXToQV929iQkqXSCMU9piwE VjGzlPmbaj651ddM+N8xvXUbNSqE638LXyLd/j0nt/vWQKKOIfbYvClnTxLL0heX9yahr67V+6Bk4 fBFonEe2ArCge5Ky04VnRADuBUhYFSKq8ST1bAjn+2/G2c2ZzoOV/c4TYpNwH7uYPEAOs1Lyp4bbA PPk0VRzYkYECRAiHaLYNrnkVWXxwZ4XSm3vrsDTgxZYX9jta4OHJ7phZ7B8v0CpDoHful1qPLUUWM JmbuAemB5oMRNyvrVueA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ouxyl-00CMRe-Hp; Tue, 15 Nov 2022 15:36:03 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1ouxyi-00CMPo-IT for linux-arm-kernel@lists.infradead.org; Tue, 15 Nov 2022 15:36:02 +0000 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 ams.source.kernel.org (Postfix) with ESMTPS id CD274B81999; Tue, 15 Nov 2022 15:35:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CDC18C433D6; Tue, 15 Nov 2022 15:35:53 +0000 (UTC) Date: Tue, 15 Nov 2022 15:35:49 +0000 From: Catalin Marinas To: Topi Miettinen Cc: Joey Gouly , Kees Cook , Andrew Morton , Lennart Poettering , Zbigniew =?utf-8?Q?J=C4=99drzejewski-Szmek?= , Alexander Viro , 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, nd@arm.com, shuah@kernel.org Subject: Re: [PATCH v1 1/2] mm: Implement memory-deny-write-execute as a prctl Message-ID: References: <20221026150457.36957-1-joey.gouly@arm.com> <20221026150457.36957-2-joey.gouly@arm.com> <202210281053.904BE2F@keescook> <20221110112714.GA1201@e124191.cambridge.arm.com> <45419a7d-04dd-2749-2534-6ba3bbd5d060@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <45419a7d-04dd-2749-2534-6ba3bbd5d060@gmail.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221115_073600_983072_EEF56103 X-CRM114-Status: GOOD ( 41.42 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, Nov 12, 2022 at 08:11:24AM +0200, Topi Miettinen wrote: > On 10.11.2022 14.03, Catalin Marinas wrote: > > On Thu, Nov 10, 2022 at 11:27:14AM +0000, Joey Gouly wrote: > > > On Fri, Oct 28, 2022 at 11:51:00AM -0700, Kees Cook wrote: > > > > On Wed, Oct 26, 2022 at 04:04:56PM +0100, Joey Gouly wrote: > > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > > > > index 099468aee4d8..42eaf6683216 100644 > > > > > --- a/mm/mmap.c > > > > > +++ b/mm/mmap.c > > > > > @@ -1409,6 +1409,9 @@ unsigned long do_mmap(struct file *file, unsigned long addr, > > > > > vm_flags |= VM_NORESERVE; > > > > > } > > > > > + if (map_deny_write_exec(NULL, vm_flags)) > > > > > + return -EACCES; > > > > > + > > > > > > > > This seems like the wrong place to do the check -- that the vma argument > > > > is a hard-coded "NULL" is evidence that something is wrong. Shouldn't > > > > it live in mmap_region()? What happens with MAP_FIXED, when there is > > > > an underlying vma? i.e. an MAP_FIXED will, I think, bypass the intended > > > > check. For example, we had "c" above: > > > > > > > > c) mmap(PROT_READ); > > > > mprotect(PROT_READ|PROT_EXEC); // fails > > > > > > > > But this would allow another case: > > > > > > > > e) addr = mmap(..., PROT_READ, ...); > > > > mmap(addr, ..., PROT_READ | PROT_EXEC, MAP_FIXED, ...); // passes > > > > > > I can move the check into mmap_region() but it won't fix the MAP_FIXED > > > example that you showed here. > > > > > > mmap_region() calls do_mas_munmap(..) which will unmap overlapping regions. > > > However the `vma` for the 'old' region is not kept around, and a new vma will > > > be allocated later on "vma = vm_area_alloc(mm);", and the vm_flags are just set > > > to what is passed into mmap_region(), so map_deny_write_exec(vma, vm_flags) > > > will just be as good as passing NULL. > > > > > > It's possible to save the vm_flags from the region that is unmapped, but Catalin > > > suggested it might be better if that is part of a later extension, what do you > > > think? > > > > I thought initially we should keep the behaviour close to what systemd > > achieves via SECCOMP while only relaxing an mprotect(PROT_EXEC) if the > > vma is already executable (i.e. check actual permission change not just > > the PROT_* flags). > > > > We could pass the old vm_flags for that region (and maybe drop the vma > > pointer entirely, just check old and new vm_flags). But this feels like > > tightening slightly systemd's MDWE approach. If user-space doesn't get > > confused by this, I'm fine to go with it. Otherwise we can add a new > > flag later for this behaviour > > > > I guess that's more of a question for Topi on whether point tightening > > point (e) is feasible/desirable. > > I think we want 1:1 compatibility with seccomp() for the basic version, so > MAP_FIXED shouldn't change the verdict. Later we can introduce more versions > (perhaps even less strict, too) when it's requested by configuration, like > MemoryDenyWriteExecute=[relaxed | strict]. Are you ok with allowing mprotect(PROT_EXEC|PROT_BTI) if the mapping is already PROT_EXEC? Or you'd rather reject that as well? -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel