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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham 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 26E58C282DD for ; Thu, 23 May 2019 09:04:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E37A82133D for ; Thu, 23 May 2019 09:04:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730049AbfEWJEh (ORCPT ); Thu, 23 May 2019 05:04:37 -0400 Received: from foss.arm.com ([217.140.101.70]:40630 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726230AbfEWJEh (ORCPT ); Thu, 23 May 2019 05:04:37 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 409B2341; Thu, 23 May 2019 02:04:36 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A78AC3F575; Thu, 23 May 2019 02:04:30 -0700 (PDT) Date: Thu, 23 May 2019 10:04:28 +0100 From: Catalin Marinas To: Evgenii Stepanov Cc: Andrey Konovalov , Linux ARM , Linux Memory Management List , LKML , amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, kvm@vger.kernel.org, "open list:KERNEL SELFTEST FRAMEWORK" , Vincenzo Frascino , Will Deacon , Mark Rutland , Andrew Morton , Greg Kroah-Hartman , Kees Cook , Yishai Hadas , Felix Kuehling , Alexander Deucher , Christian Koenig , Mauro Carvalho Chehab , Jens Wiklander , Alex Williamson , Leon Romanovsky , Dmitry Vyukov , Kostya Serebryany , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Robin Murphy , Luc Van Oostenryck , Dave Martin , Kevin Brodsky , Szabolcs Nagy Subject: Re: [PATCH v15 05/17] arms64: untag user pointers passed to memory syscalls Message-ID: <20190523090427.GA44383@arrakis.emea.arm.com> References: <00eb4c63fefc054e2c8d626e8fedfca11d7c2600.1557160186.git.andreyknvl@google.com> <20190522114910.emlckebwzv2qz42i@mbp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Wed, May 22, 2019 at 02:16:57PM -0700, Evgenii Stepanov wrote: > On Wed, May 22, 2019 at 4:49 AM Catalin Marinas wrote: > > On Mon, May 06, 2019 at 06:30:51PM +0200, Andrey Konovalov wrote: > > > This patch is a part of a series that extends arm64 kernel ABI to allow to > > > pass tagged user pointers (with the top byte set to something else other > > > than 0x00) as syscall arguments. > > > > > > This patch allows tagged pointers to be passed to the following memory > > > syscalls: brk, get_mempolicy, madvise, mbind, mincore, mlock, mlock2, > > > mmap, mmap_pgoff, mprotect, mremap, msync, munlock, munmap, > > > remap_file_pages, shmat and shmdt. > > > > > > This is done by untagging pointers passed to these syscalls in the > > > prologues of their handlers. > > > > I'll go through them one by one to see if we can tighten the expected > > ABI while having the MTE in mind. > > > > > diff --git a/arch/arm64/kernel/sys.c b/arch/arm64/kernel/sys.c > > > index b44065fb1616..933bb9f3d6ec 100644 > > > --- a/arch/arm64/kernel/sys.c > > > +++ b/arch/arm64/kernel/sys.c > > > @@ -35,10 +35,33 @@ SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len, > > > { > > > if (offset_in_page(off) != 0) > > > return -EINVAL; > > > - > > > + addr = untagged_addr(addr); > > > return ksys_mmap_pgoff(addr, len, prot, flags, fd, off >> PAGE_SHIFT); > > > } > > > > If user passes a tagged pointer to mmap() and the address is honoured > > (or MAP_FIXED is given), what is the expected return pointer? Does it > > need to be tagged with the value from the hint? > > For HWASan the most convenient would be to use the tag from the hint. > But since in the TBI (not MTE) mode the kernel has no idea what > meaning userspace assigns to pointer tags, perhaps it should not try > to guess, and should return raw (zero-tagged) address instead. Then, just to relax the ABI for hwasan, shall we simply disallow tagged pointers on mmap() arguments? We can leave them in for mremap(old_address), madvise(). > > With MTE, we may want to use this as a request for the default colour of > > the mapped pages (still under discussion). > > I like this - and in that case it would make sense to return the > pointer that can be immediately dereferenced without crashing the > process, i.e. with the matching tag. This came up from the Android investigation work where large memory allocations (using mmap) could be more efficiently pre-tagged by the kernel on page fault. Not sure about the implementation details yet. -- Catalin