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=-15.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 D29F1C11F66 for ; Tue, 29 Jun 2021 10:03:32 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9B26361CB1 for ; Tue, 29 Jun 2021 10:03:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9B26361CB1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:Cc:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=xQY5R0e5pzwwgRxiVzpP3R9oulZfTYIctBRy6GW/iHk=; b=Hdz4HgzRRcxRmYclNmVr2lLKcX aaS08F1netiVPyIb1V6+uS4dJNIeZjmOxksgFMlAUD0BINyZwOsOWZloyl0s2e70KVZyUsaUo3DzY 5e21O/PyeZDkLI3Bj0e9CWbNP5HPm5Fn4sFaPQTAoayElqrm0AtkSptkrrzN3fx36MnzzYdO7DpEg 1gzKTxgjjLT6cNoqljN5ZKMtsVn5kql9bW64ASfzSai8+AYnPqGU7xLqWTdfDlDtdShtjMUxViQM5 TsZfxANc2NJg3EioeG4C9Lc2mSaNnBXw8c22MOZ9UcjpXH7NQKCnBDh2B4UmbdDjp6PzQmikoXDaG ldPfys1g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lyAYu-00ATFb-2f; Tue, 29 Jun 2021 10:01:48 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lyAYq-00ATEv-9a for linux-arm-kernel@lists.infradead.org; Tue, 29 Jun 2021 10:01:46 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2DF651042; Tue, 29 Jun 2021 03:01:39 -0700 (PDT) Received: from [10.57.46.146] (unknown [10.57.46.146]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E36AC3F694; Tue, 29 Jun 2021 03:01:36 -0700 (PDT) Subject: Re: [BUG] arm64: an infinite loop in generic_perform_write() To: Catalin Marinas Cc: Chen Huang , Al Viro , Matthew Wilcox , Christoph Hellwig , Mark Rutland , Andrew Morton , Stephen Rothwell , Randy Dunlap , Will Deacon , Linux ARM , linux-mm , open list References: <1c635945-fb25-8871-7b34-f475f75b2caf@huawei.com> <27fbb8c1-2a65-738f-6bec-13f450395ab7@arm.com> <20210624185554.GC25097@arm.com> <20210625103905.GA20835@arm.com> <7f14271a-9b2f-1afc-3caf-c4e5b36efa73@arm.com> <20210629083052.GA10900@arm.com> From: Robin Murphy Message-ID: Date: Tue, 29 Jun 2021 11:01:31 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210629083052.GA10900@arm.com> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210629_030144_492090_B946A233 X-CRM114-Status: GOOD ( 24.49 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2021-06-29 09:30, Catalin Marinas wrote: > On Mon, Jun 28, 2021 at 05:22:30PM +0100, Robin Murphy wrote: >> From: Robin Murphy >> Subject: [PATCH] arm64: Avoid premature usercopy failure >> >> Al reminds us that the usercopy API must only return complete failure >> if absolutely nothing could be copied. Currently, if userspace does >> something silly like giving us an unaligned pointer to Device memory, >> or a size which overruns MTE tag bounds, we may fail to honour that >> requirement when faulting on a multi-byte access even though a smaller >> access could have succeeded. >> >> Add a mitigation to the fixup routines to fall back to a single-byte >> copy if we faulted on a larger access before anything has been written >> to the destination, to guarantee making *some* forward progress. We >> needn't be too concerned about the overall performance since this should >> only occur when callers are doing something a bit dodgy in the first >> place. Particularly broken userspace might still be able to trick >> generic_perform_write() into an infinite loop by targeting write() at >> an mmap() of some read-only device register where the fault-in load >> succeeds but any store synchronously aborts such that copy_to_user() is >> genuinely unable to make progress, but, well, don't do that... >> >> Reported-by: Chen Huang >> Suggested-by: Al Viro >> Signed-off-by: Robin Murphy > > Thanks Robin for putting this together. I'll write some MTE kselftests > to check for regressions in the future. > >> diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S >> index 95cd62d67371..5b720a29a242 100644 >> --- a/arch/arm64/lib/copy_from_user.S >> +++ b/arch/arm64/lib/copy_from_user.S >> @@ -29,7 +29,7 @@ >> .endm >> .macro ldrh1 reg, ptr, val >> - user_ldst 9998f, ldtrh, \reg, \ptr, \val >> + user_ldst 9997f, ldtrh, \reg, \ptr, \val >> .endm >> .macro strh1 reg, ptr, val >> @@ -37,7 +37,7 @@ >> .endm >> .macro ldr1 reg, ptr, val >> - user_ldst 9998f, ldtr, \reg, \ptr, \val >> + user_ldst 9997f, ldtr, \reg, \ptr, \val >> .endm >> .macro str1 reg, ptr, val >> @@ -45,7 +45,7 @@ >> .endm >> .macro ldp1 reg1, reg2, ptr, val >> - user_ldp 9998f, \reg1, \reg2, \ptr, \val >> + user_ldp 9997f, \reg1, \reg2, \ptr, \val >> .endm >> .macro stp1 reg1, reg2, ptr, val >> @@ -53,8 +53,10 @@ >> .endm >> end .req x5 >> +srcin .req x15 >> SYM_FUNC_START(__arch_copy_from_user) >> add end, x0, x2 >> + mov srcin, x1 >> #include "copy_template.S" >> mov x0, #0 // Nothing to copy >> ret >> @@ -63,6 +65,12 @@ EXPORT_SYMBOL(__arch_copy_from_user) >> .section .fixup,"ax" >> .align 2 >> +9997: cmp dst, dstin >> + b.ne 9998f >> + // Before being absolutely sure we couldn't copy anything, try harder >> +USER(9998f, ldtrb tmp1w, [srcin]) >> + strb tmp1w, [dstin] >> + add dst, dstin, #1 > > Nitpick: can we do just strb tmb1w, [dst], #1? It matches the strb1 > macro in this file. Oh, of course; I think I befuddled myself there and failed to consider that by this point we've already mandated that dstin == dst (so that we can use srcin because src may have advanced already), so in fact we *can* use dst as the base register to avoid the shuffling, and post-index this one. I'll clean that up. > Either way, it looks fine to me. > > Reviewed-by: Catalin Marinas Thanks! Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel