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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 09CF0C3A5A1 for ; Thu, 22 Aug 2019 16:37:37 +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 D1AA0206B7 for ; Thu, 22 Aug 2019 16:37:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="cT9jYcoe" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D1AA0206B7 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=+t6/+WW0CCM3jOQ/PJOr76/VIOL+r3mi1yYqQopAs48=; b=cT9jYcoeZ34vXq DnqSDxFUWb8eXcwLy9CGVhkC8GeJecB7CIuVSke+SYcI3PD8Au0m0WM3YXWu2xmqLDx1opAv4Rtwe GH9ZMX5Ni/hZnbSnuvvfb1/07gPZ2mHysBCftG+NNuXH8QrbTaZxBHaTgTfXpi5xfTBtK+r/lV4Xj FKjg74OPuN+3zpH7wfrnDFlj/XNT3TnOIESjA24bNi2eYavS/7HSV6uWZQVnhmbY/mnd0F9kMwZMf koB2/+DQGhlLcz3zdgMC4W1L0pCHrsiFYgYnFIVgZrnJ3H8tYogVTcT3xiEnyxbPAt4t6bhPhP8lG hW/Ah8Z15Yov6iWz05ng==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i0q5g-0006cc-7p; Thu, 22 Aug 2019 16:37:36 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i0q5Y-0006XG-2C for linux-arm-kernel@lists.infradead.org; Thu, 22 Aug 2019 16:37:34 +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 0F16E28; Thu, 22 Aug 2019 09:37:27 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5B9283F718; Thu, 22 Aug 2019 09:37:25 -0700 (PDT) Date: Thu, 22 Aug 2019 17:37:23 +0100 From: Dave Martin To: Catalin Marinas Subject: Re: [PATCH v9 3/3] arm64: Relax Documentation/arm64/tagged-pointers.rst Message-ID: <20190822163723.GF27757@arm.com> References: <20190821164730.47450-1-catalin.marinas@arm.com> <20190821164730.47450-4-catalin.marinas@arm.com> <20190821173352.yqfgaozi7nfhcofg@willie-the-truck> <20190821184649.GD27757@arm.com> <20190822155531.GB55798@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190822155531.GB55798@arrakis.emea.arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190822_093728_222286_526BAB4B X-CRM114-Status: GOOD ( 25.66 ) 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: linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Kevin Brodsky , Will Deacon , linux-mm@kvack.org, Andrew Morton , Vincenzo Frascino , Will Deacon , Dave Hansen , linux-arm-kernel@lists.infradead.org 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 Thu, Aug 22, 2019 at 04:55:32PM +0100, Catalin Marinas wrote: > On Wed, Aug 21, 2019 at 07:46:51PM +0100, Dave P Martin wrote: > > On Wed, Aug 21, 2019 at 06:33:53PM +0100, Will Deacon wrote: > > > On Wed, Aug 21, 2019 at 05:47:30PM +0100, Catalin Marinas wrote: > > > > @@ -59,6 +63,11 @@ be preserved. > > > > The architecture prevents the use of a tagged PC, so the upper byte will > > > > be set to a sign-extension of bit 55 on exception return. > > > > > > > > +This behaviour is maintained when the AArch64 Tagged Address ABI is > > > > +enabled. In addition, with the exceptions above, the kernel will > > > > +preserve any non-zero tags passed by the user via syscalls and stored in > > > > +kernel data structures (e.g. ``set_robust_list()``, ``sigaltstack()``). > > > > sigaltstack() is interesting, since we don't support tagged stacks. > > We should support tagged SP with the new ABI as they'll be required for > MTE. sigaltstack() and clone() are the two syscalls that come to mind > here. > > > Do we keep the ss_sp tag in the kernel, but squash it when delivering > > a signal to the alternate stack? > > We don't seem to be doing any untagging, so we just just use whatever > the caller asked for. We may need a small test to confirm. If we want to support tagged SP, then I guess we shouldn't be squashing the tag anywhere. A test for that would be sensible to have. > That said, on_sig_stack() probably needs some untagging as it does user > pointer arithmetics with potentially different tags. Good point. > > > Hmm. I can see the need to provide this guarantee for things like > > > set_robust_list(), but the problem is that the statement above is too broad > > > and isn't strictly true: for example, mmap() doesn't propagate the tag of > > > its address parameter into the VMA. > > > > > > So I think we need to nail this down a bit more, but I'm having a really > > > hard time coming up with some wording :( > > > > Time for some creative vagueness? > > > > We can write a statement of our overall intent, along with examples of > > a few cases where the tag should and should not be expected to emerge > > intact. > > > > There is no foolproof rule, unless we can rewrite history... > > I would expect the norm to be the preservation of tags with a few > exceptions. The only ones I think where we won't preserve the tags are > mmap, mremap, brk (apart from the signal stuff already mentioned in the > current tagged-pointers.rst doc). > > So I can remove this paragraph altogether and add a note in part 3 of > the tagged-address-abi.rst document that mmap/mremap/brk do not preserve > the tag information. Deleting text is always a good idea ;) There are other cases like (non-)propagation of the tag to si_addr when a fault is reported via a signal, but I think we already have appropriate wording to cover that. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel