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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 12E5EC4332F for ; Thu, 10 Nov 2022 12:03:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230269AbiKJMDi (ORCPT ); Thu, 10 Nov 2022 07:03:38 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54922 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229575AbiKJMDg (ORCPT ); Thu, 10 Nov 2022 07:03:36 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E33C1788D for ; Thu, 10 Nov 2022 04:03:34 -0800 (PST) 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 sin.source.kernel.org (Postfix) with ESMTPS id 50562CE2256 for ; Thu, 10 Nov 2022 12:03:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBD5DC433D6; Thu, 10 Nov 2022 12:03:27 +0000 (UTC) Date: Thu, 10 Nov 2022 12:03:24 +0000 From: Catalin Marinas To: Joey Gouly Cc: Kees Cook , Andrew Morton , Lennart Poettering , Zbigniew =?utf-8?Q?J=C4=99drzejewski-Szmek?= , Alexander Viro , 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, 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221110112714.GA1201@e124191.cambridge.arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Catalin 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 A9084C4332F for ; Thu, 10 Nov 2022 12:05:42 +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=D7NJ6VoNmLT88dhfOmlKb4rSWb9wWUt4zGtOaEyww/A=; b=jixG67F7u9+omt I0xAmHQjTKeYxZZxnZa7F3+L6ldUYesUezroxMh70iWzfAz08binANQPVpF/+65A+T9/qaUAgGO1C 1jB+BxZa1iVZw35z9+8MPwJUxqwHz6FEZxgkxcpJWOL5UVApt9DNrMkNs/eyBBqHPar+VarTZ9IUe pIXsfq94238dLuFCxHLNZzq2TsvEhGQA1Ck/q+bv/dH6dlq3CukrGXV1sNXYFIM9IbXRC9ADBffC6 Gu1lgk7RdXypkcas6t5Mx2cbeF+v3d6BLCV9+a52Ri1Crt3WgNUk6RetMTNAXJHGr01IyiErx2caq L+8JjBRI/w4AlQKmWxKA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ot6IO-005dQd-NQ; Thu, 10 Nov 2022 12:04:37 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1ot6HM-005cwv-7a for linux-arm-kernel@lists.infradead.org; Thu, 10 Nov 2022 12:03:33 +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 dfw.source.kernel.org (Postfix) with ESMTPS id 2B87361557; Thu, 10 Nov 2022 12:03:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBD5DC433D6; Thu, 10 Nov 2022 12:03:27 +0000 (UTC) Date: Thu, 10 Nov 2022 12:03:24 +0000 From: Catalin Marinas To: Joey Gouly Cc: Kees Cook , Andrew Morton , Lennart Poettering , Zbigniew =?utf-8?Q?J=C4=99drzejewski-Szmek?= , Alexander Viro , 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, 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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20221110112714.GA1201@e124191.cambridge.arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221110_040332_342563_8EE488D3 X-CRM114-Status: GOOD ( 32.48 ) 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 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. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel