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[217.140.101.70]) by mx.google.com with ESMTP id z17si4959206eju.125.2019.05.23.02.04.37 for ; Thu, 23 May 2019 02:04:37 -0700 (PDT) Received-SPF: pass (google.com: domain of catalin.marinas@arm.com designates 217.140.101.70 as permitted sender) client-ip=217.140.101.70; Authentication-Results: mx.google.com; spf=pass (google.com: domain of catalin.marinas@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=catalin.marinas@arm.com 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) 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 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