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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 611AAC433E1 for ; Thu, 27 Aug 2020 14:56:51 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 140BC22B4B for ; Thu, 27 Aug 2020 14:56:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 140BC22B4B 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 874C98E0008; Thu, 27 Aug 2020 10:56:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8251B8E0006; Thu, 27 Aug 2020 10:56:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 73BAA8E0008; Thu, 27 Aug 2020 10:56:50 -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 5EF138E0006 for ; Thu, 27 Aug 2020 10:56:50 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id F31E03642 for ; Thu, 27 Aug 2020 14:56:49 +0000 (UTC) X-FDA: 77196650538.15.pan88_5c084462706e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 037F11814B0D4 for ; Thu, 27 Aug 2020 14:56:48 +0000 (UTC) X-HE-Tag: pan88_5c084462706e X-Filterd-Recvd-Size: 4494 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf02.hostedemail.com (Postfix) with ESMTP for ; Thu, 27 Aug 2020 14:56:48 +0000 (UTC) Received: from gaia (unknown [46.69.195.127]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 178032054F; Thu, 27 Aug 2020 14:56:44 +0000 (UTC) Date: Thu, 27 Aug 2020 15:56:42 +0100 From: Catalin Marinas To: Andrey Konovalov Cc: Vincenzo Frascino , Dmitry Vyukov , kasan-dev , Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Elena Petrova , Branislav Rankov , Kevin Brodsky , Will Deacon , Andrew Morton , Linux ARM , Linux Memory Management List , LKML Subject: Re: [PATCH 21/35] arm64: mte: Add in-kernel tag fault handler Message-ID: <20200827145642.GO29264@gaia> References: <20200827095429.GC29264@gaia> <20200827131045.GM29264@gaia> 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-Rspamd-Queue-Id: 037F11814B0D4 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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, Aug 27, 2020 at 03:34:42PM +0200, Andrey Konovalov wrote: > On Thu, Aug 27, 2020 at 3:10 PM Catalin Marinas wrote: > > On Thu, Aug 27, 2020 at 02:31:23PM +0200, Andrey Konovalov wrote: > > > On Thu, Aug 27, 2020 at 11:54 AM Catalin Marinas > > > wrote: > > > > On Fri, Aug 14, 2020 at 07:27:03PM +0200, Andrey Konovalov wrote: > > > > > +static int do_tag_recovery(unsigned long addr, unsigned int esr, > > > > > + struct pt_regs *regs) > > > > > +{ > > > > > + report_tag_fault(addr, esr, regs); > > > > > + > > > > > + /* Skip over the faulting instruction and continue: */ > > > > > + arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE); > > > > > > > > Ooooh, do we expect the kernel to still behave correctly after this? I > > > > thought the recovery means disabling tag checking altogether and > > > > restarting the instruction rather than skipping over it. [...] > > > Can we disable MTE, reexecute the instruction, and then reenable MTE, > > > or something like that? > > > > If you want to preserve the MTE enabled, you could single-step the > > instruction or execute it out of line, though it's a bit more convoluted > > (we have a similar mechanism for kprobes/uprobes). > > > > Another option would be to attempt to set the matching tag in memory, > > under the assumption that it is writable (if it's not, maybe it's fine > > to panic). Not sure how this interacts with the slub allocator since, > > presumably, the logical tag in the pointer is wrong rather than the > > allocation one. > > > > Yet another option would be to change the tag in the register and > > re-execute but this may confuse the compiler. > > Which one of these would be simpler to implement? Either 2 or 3 would be simpler (re-tag the memory location or the pointer) with the caveats I mentioned. Also, does the slab allocator need to touch the memory on free with a tagged pointer? Otherwise slab may hit an MTE fault itself. > Perhaps we could somehow only skip faulting instructions that happen > in the KASAN test module?.. Decoding stack trace would be an option, > but that's a bit weird. If you want to restrict this to the KASAN tests, just add some MTE-specific accessors with a fixup entry similar to get_user/put_user. __do_kernel_fault() (if actually called) will invoke the fixup code which skips the access and returns an error. This way KASAN tests can actually verify that tag checking works, I'd find this a lot more useful. -- Catalin