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=-5.2 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 DFBF9C433E6 for ; Fri, 28 Aug 2020 09:56:49 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 825E9208FE for ; Fri, 28 Aug 2020 09:56:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 825E9208FE 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 E41786B0003; Fri, 28 Aug 2020 05:56:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DF1A06B0006; Fri, 28 Aug 2020 05:56:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D09D66B0007; Fri, 28 Aug 2020 05:56:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0024.hostedemail.com [216.40.44.24]) by kanga.kvack.org (Postfix) with ESMTP id BA0DB6B0003 for ; Fri, 28 Aug 2020 05:56:48 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 8CC119418 for ; Fri, 28 Aug 2020 09:56:48 +0000 (UTC) X-FDA: 77199523296.23.horn02_1a1458027074 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin23.hostedemail.com (Postfix) with ESMTP id 5532337604 for ; Fri, 28 Aug 2020 09:56:48 +0000 (UTC) X-HE-Tag: horn02_1a1458027074 X-Filterd-Recvd-Size: 5353 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf03.hostedemail.com (Postfix) with ESMTP for ; Fri, 28 Aug 2020 09:56:47 +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 3CAEB208D5; Fri, 28 Aug 2020 09:56:44 +0000 (UTC) Date: Fri, 28 Aug 2020 10:56:41 +0100 From: Catalin Marinas To: Evgenii Stepanov Cc: Andrey Konovalov , Vincenzo Frascino , Dmitry Vyukov , kasan-dev , Andrey Ryabinin , Alexander Potapenko , Marco Elver , 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: <20200828095641.GD3169@gaia> References: <20200827095429.GC29264@gaia> <20200827131045.GM29264@gaia> <20200827145642.GO29264@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: 5532337604 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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 12:14:26PM -0700, Evgenii Stepanov wrote: > On Thu, Aug 27, 2020 at 7:56 AM Catalin Marinas wrote: > > 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. > > Changing the memory tag can cause faults in other threads, and that > could be very confusing. It could indeed trigger a chain of faults. It's not even other threads, it could be the same thread in a different function. > Probably the safest thing is to retag the register, single step and > then retag it back, but be careful with the instructions that change > the address register (like ldr x0, [x0]). This gets complicated if you have to parse the opcode. If you can single-step, just set PSTATE.TCO for the instruction. But the single-step machinery gets more complicated, probably interacts badly with kprobes. I think the best option is to disable the MTE checks in TCF on an _unhandled_ kernel fault, report and continue. For the KASAN tests, add accessors similar to get_user/put_user which are able to handle the fault and return an error. Such accessors, since they have a fixup handler, would not lead to the MTE checks being disabled. -- Catalin