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 63AE8C433DF for ; Thu, 27 Aug 2020 13:10:53 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2ACD6207CD for ; Thu, 27 Aug 2020 13:10:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2ACD6207CD 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 89BC08E000D; Thu, 27 Aug 2020 09:10:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 84C428E0006; Thu, 27 Aug 2020 09:10:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 73BB48E000D; Thu, 27 Aug 2020 09:10:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0102.hostedemail.com [216.40.44.102]) by kanga.kvack.org (Postfix) with ESMTP id 5E3AD8E0006 for ; Thu, 27 Aug 2020 09:10:52 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 1E62E181AEF15 for ; Thu, 27 Aug 2020 13:10:52 +0000 (UTC) X-FDA: 77196383544.23.paste42_3c0c8672706d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin23.hostedemail.com (Postfix) with ESMTP id E2B5537608 for ; Thu, 27 Aug 2020 13:10:51 +0000 (UTC) X-HE-Tag: paste42_3c0c8672706d X-Filterd-Recvd-Size: 4532 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Thu, 27 Aug 2020 13:10:51 +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 10065206F0; Thu, 27 Aug 2020 13:10:47 +0000 (UTC) Date: Thu, 27 Aug 2020 14:10:45 +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: <20200827131045.GM29264@gaia> References: <20200827095429.GC29264@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: E2B5537608 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 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. > > The intention is to be able to catch multiple MTE faults without > panicking or disabling MTE when executing KASAN tests (those do > multiple bad accesses one after another). The problem is that for MTE synchronous tag check faults, the access has not happened, so you basically introduce memory corruption by skipping the access. > We do arm64_skip_faulting_instruction() for software tag-based KASAN > too, it's not ideal, but works for testing purposes. IIUC, KASAN only skips over the brk instruction which doesn't have any other side-effects. Has the actual memory access taken place when it hits the brk? > 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. > When running in-kernel MTE in production, we'll either panic or > disable MTE after the first fault. This was controlled by the > panic_on_mte_fault option Vincenzo initially had. I prefer to disable MTE, print something and continue, but no panic. > > We only skip if we emulated it. > > I'm not sure I understand this part, what do you mean by emulating? Executing it out of line or other form of instruction emulation (see arch/arm64/kernel/probes/simulate-insn.c) so that the access actually takes place. But you can single-step or experiment with some of the other tricks above. -- Catalin