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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 895DEC433E0 for ; Thu, 28 May 2020 16:35:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 401F920721 for ; Thu, 28 May 2020 16:35:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 401F920721 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C75638001A; Thu, 28 May 2020 12:34:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C4B8180010; Thu, 28 May 2020 12:34:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B88888001A; Thu, 28 May 2020 12:34:59 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0099.hostedemail.com [216.40.44.99]) by kanga.kvack.org (Postfix) with ESMTP id A2DAA80010 for ; Thu, 28 May 2020 12:34:59 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 52305180ACF0E for ; Thu, 28 May 2020 16:34:59 +0000 (UTC) X-FDA: 76866677118.25.rice93_601ca8d224907 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin25.hostedemail.com (Postfix) with ESMTP id EAF8C180385ED for ; Thu, 28 May 2020 16:34:20 +0000 (UTC) X-HE-Tag: rice93_601ca8d224907 X-Filterd-Recvd-Size: 6073 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Thu, 28 May 2020 16:34:20 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E2A7D30E; Thu, 28 May 2020 09:34:17 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 165B93F305; Thu, 28 May 2020 09:34:15 -0700 (PDT) Date: Thu, 28 May 2020 17:34:13 +0100 From: Catalin Marinas To: Szabolcs Nagy Cc: Peter Collingbourne , Linux ARM , linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon , Dave P Martin , Vincenzo Frascino , Kevin Brodsky , Andrey Konovalov , Evgenii Stepanov , nd@arm.com Subject: Re: [PATCH v4 11/26] arm64: mte: Add PROT_MTE support to mmap() and mprotect() Message-ID: <20200528163412.GC2961@gaia> References: <20200515171612.1020-1-catalin.marinas@arm.com> <20200515171612.1020-12-catalin.marinas@arm.com> <20200528091445.GA2961@gaia> <20200528110509.GA18623@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200528110509.GA18623@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: EAF8C180385ED X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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, May 28, 2020 at 12:05:09PM +0100, Szabolcs Nagy wrote: > The 05/28/2020 10:14, Catalin Marinas wrote: > > On Wed, May 27, 2020 at 11:57:39AM -0700, Peter Collingbourne wrote: > > > On Fri, May 15, 2020 at 10:16 AM Catalin Marinas > > > wrote: > > > > To enable tagging on a memory range, the user must explicitly opt in via > > > > a new PROT_MTE flag passed to mmap() or mprotect(). Since this is a new > > > > memory type in the AttrIndx field of a pte, simplify the or'ing of these > > > > bits over the protection_map[] attributes by making MT_NORMAL index 0. > > > > > > Should the userspace stack always be mapped as if with PROT_MTE if the > > > hardware supports it? Such a change would be invisible to non-MTE > > > aware userspace since it would already need to opt in to tag checking > > > via prctl. This would let userspace avoid a complex stack > > > initialization sequence when running with stack tagging enabled on the > > > main thread. > > > > I don't think the stack initialisation is that difficult. On program > > startup (can be the dynamic loader). Something like (untested): > > > > register unsigned long stack asm ("sp"); > > unsigned long page_sz = sysconf(_SC_PAGESIZE); > > > > mprotect((void *)(stack & ~(page_sz - 1)), page_sz, > > PROT_READ | PROT_WRITE | PROT_MTE | PROT_GROWSDOWN); > > > > (the essential part it PROT_GROWSDOWN so that you don't have to specify > > a stack lower limit) > > does this work even if the currently mapped stack is more than page_sz? > determining the mapped main stack area is i think non-trivial to do in > userspace (requires parsing /proc/self/maps or similar). Because of PROT_GROWSDOWN, the kernel adjusts the start of the range down automatically. It is potentially problematic if the top of the stack is more than a page away and you want the whole stack coloured. I haven't run a test but my reading of the kernel code is that the stack vma would be split in this scenario, so the range beyond sp+page_sz won't have PROT_MTE set. My assumption is that if you do this during program start, the stack is smaller than a page. Alternatively, could we use argv or envp to determine the top of the user stack (the bottom is taken care of by the kernel)? > > I'm fine, however, with enabling PROT_MTE on the main stack based on > > some ELF note. > > note that would likely mean an elf note on the dynamic linker > (because a dynamic linked executable may not be loaded by the > kernel and ctors in loaded libs run before the executable entry > code anyway, so the executable alone cannot be in charge of this > decision) i.e. one global switch for all dynamic linked binaries. I guess parsing such note in the kernel is only useful for static binaries. > i think a dynamic linker can map a new stack and switch to it > if it needs to control the properties of the stack at runtime > (it's wasteful though). There is already user code to check for HWCAP2_MTE and the prctl(), so adding an mprotect() doesn't look like a significant overhead. > and i think there should be a runtime mechanism for the brk area: > it should be possible to request that future brk expansions are > mapped as PROT_MTE so an mte aware malloc implementation can use > brk. i think this is not important in the initial design, but if > a prctl flag can do it that may be useful to add (may be at a > later time). Looking at the kernel code briefly, I think this would work. We do end up with two vmas for the brk, only the expansion having PROT_MTE, and I'd to find a way to store the extra flag. >From a coding perspective, it's easier to just set PROT_MTE by default on both brk and initial stack ;) (VM_DATA_DEFAULT_FLAGS). > (and eventually there should be a way to use PROT_MTE on > writable global data and appropriate code generation that > takes colors into account when globals are accessed, but > that requires significant ELF, ld.so and compiler changes, > that need not be part of the initial mte design). The .data section needs to be driven by the ELF information. It's also a file mapping and we don't support PROT_MTE on them even if MAP_PRIVATE. There are complications like DAX where the file you mmap for CoW may be hosted on memory that does not support MTE (copied to RAM on write). Is there a use-case for global data to be tagged? -- Catalin