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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 ED545C8300D for ; Thu, 30 Apr 2020 09:50:16 +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 901F22082E for ; Thu, 30 Apr 2020 09:50:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="rZ3b33ke" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 901F22082E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-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.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=bjn6WsLrHSlUL+NhIGNC5uJVr38ibcQhrpxUyc/rUuE=; b=rZ3b33keSGEGr1 xohkwJSpPCRwPPu72U3KcGFqftEH7atr/NgP//na42BtnkGKITmgE777/P16u/m8jhT+qQmimUiny syIGCztuiKJocVGsr/X88xTgyTgY2n02B6SdiDfus9Ki7/0ASew1TpRAVB6lsHQDZnqrMj8zRuJtc xj9d8OiOVKT6VS0hQyAH2az2qwDgRYktHNdizCK/1VeDCk5h64FqwS3Et4S3aeIp/XIBxIEkkNjVt tIuJto1SMQsCedISRpWxYElQBX7CcXb/TKfgxuCr1zoBogs7FYAjjzUXiPd4urb5PB8hupClbvOa6 pK+oh2NMJ9HftvU8zLFg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jU5pa-0004Hp-0p; Thu, 30 Apr 2020 09:50:10 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jU5pW-0003S1-TX for linux-arm-kernel@lists.infradead.org; Thu, 30 Apr 2020 09:50:08 +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 5B4051063; Thu, 30 Apr 2020 02:50:05 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 127583F68F; Thu, 30 Apr 2020 02:50:03 -0700 (PDT) Date: Thu, 30 Apr 2020 10:50:01 +0100 From: Catalin Marinas To: Will Deacon Subject: Re: [PATCH v3] arm64: Expose original FAR_EL1 value in sigcontext Message-ID: <20200430095001.GD2717@gaia> References: <20200325174001.234803-1-pcc@google.com> <20200327191915.257116-1-pcc@google.com> <20200429210826.GA8604@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200429210826.GA8604@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200430_025007_022463_DFAA2F79 X-CRM114-Status: GOOD ( 17.00 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrey Konovalov , Kevin Brodsky , Kostya Serebryany , Evgenii Stepanov , Vincenzo Frascino , Peter Collingbourne , Linux ARM , Richard Henderson Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Apr 29, 2020 at 10:08:26PM +0100, Will Deacon wrote: > On Fri, Mar 27, 2020 at 12:19:15PM -0700, Peter Collingbourne wrote: > > The kernel currently clears the tag bits (i.e. bits 56-63) in the fault > > address exposed via siginfo.si_addr and sigcontext.fault_address. However, > > the tag bits may be needed by tools in order to accurately diagnose > > memory errors, such as HWASan [1] or future tools based on the Memory > > Tagging Extension (MTE). > > > > We should not stop clearing these bits in the existing fault address > > fields, because there may be existing userspace applications that are > > expecting the tag bits to be cleared. Instead, create a far_context in > > sigcontext (similar to the existing esr_context), and store the original > > value of FAR_EL1 (including the tag bits) there. > > > > [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html > > > > Signed-off-by: Peter Collingbourne > > --- > > v3: > > - add documentation to tagged-pointers.rst > > - update comments in sigcontext.h > > Hmm, although the code looks fine, why don't we just expose the tag in the > new field, rather than duplicate the address information? I'm nervous about > exposing privileged registers directly to userspace. That's for consistency with ESR_EL1 which we expose in a similar way, though with bits of it not relevant to user masked out. For FAR_EL1, all the bits are relevant, even if some of them are duplicated in the si_addr field. > Also, Catalin, could you elaborate on the MTE use-case please? The > architecture says that FAR_EL1[63:60] are UNKNOWN on a synchronous tag > check fault, so we'd have to *avoid* exposing them in that case! With MTE, FAR_EL1[63:60] will be cleared on sync tag check faults (not currently done as I don't have this patch in my MTE series). -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel