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=-6.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 369E1C2D0A3 for ; Mon, 16 Nov 2020 19:01:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 04E662068D for ; Mon, 16 Nov 2020 19:01:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727087AbgKPTBY (ORCPT ); Mon, 16 Nov 2020 14:01:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:52574 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727023AbgKPTBY (ORCPT ); Mon, 16 Nov 2020 14:01:24 -0500 Received: from trantor (unknown [2.26.170.190]) (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 69FBA206A1; Mon, 16 Nov 2020 19:01:21 +0000 (UTC) Date: Mon, 16 Nov 2020 19:01:18 +0000 From: Catalin Marinas To: Peter Collingbourne Cc: Evgenii Stepanov , Kostya Serebryany , Vincenzo Frascino , Dave Martin , Will Deacon , Oleg Nesterov , "Eric W. Biederman" , "James E.J. Bottomley" , Linux ARM , Kevin Brodsky , Andrey Konovalov , linux-api@vger.kernel.org, Helge Deller , David Spickett Subject: Re: [PATCH v16 6/6] arm64: expose FAR_EL1 tag bits in siginfo Message-ID: References: <81e1307108ca8ea67aa1060f6f47b34a507410f1.1605235762.git.pcc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <81e1307108ca8ea67aa1060f6f47b34a507410f1.1605235762.git.pcc@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Thu, Nov 12, 2020 at 06:53:36PM -0800, Peter Collingbourne wrote: > diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst > index eab4323609b9..19d284b70384 100644 > --- a/Documentation/arm64/tagged-pointers.rst > +++ b/Documentation/arm64/tagged-pointers.rst > @@ -53,12 +53,25 @@ visibility. > Preserving tags > --------------- > > -Non-zero tags are not preserved when delivering signals. This means that > -signal handlers in applications making use of tags cannot rely on the > -tag information for user virtual addresses being maintained for fields > -inside siginfo_t. One exception to this rule is for signals raised in > -response to watchpoint debug exceptions, where the tag information will > -be preserved. > +When delivering signals, non-zero tags are not preserved in > +siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in > +sigaction.sa_flags when the signal handler was installed. This means > +that signal handlers in applications making use of tags cannot rely > +on the tag information for user virtual addresses being maintained > +in these fields unless the flag was set. > + > +Due to architecture limitations, bits 63:60 of the fault address > +are not preserved in response to synchronous tag check faults > +(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should > +treat the values of these bits as undefined in order to accommodate > +future architecture revisions which may preserve the bits. If future architecture versions will preserve these bits, most likely we'll add a new HWCAP bit so that the user knows what's going on. But the user shouldn't rely on them being 0, just in case. > +For signals raised in response to watchpoint debug exceptions, the > +tag information will be preserved regardless of the SA_EXPOSE_TAGBITS > +flag setting. > + > +Non-zero tags are never preserved in sigcontext.fault_address > +regardless of the SA_EXPOSE_TAGBITS flag setting. We could've done it the other way around (fault_address tagged, si_addr untagged) but that would be specific to arm64, so I think we should solve it for other architectures that implement (or plan to) tagging. The fault_address in the arm64 sigcontext was an oversight, we should have removed it but when we realised it was already ABI. Anyway, I'm fine with the arm64 changes here: Reviewed-by: Catalin Marinas With Eric's ack, I'm happy to take the series through the arm64 tree, otherwise Eric's tree is fine as well. Thanks. -- Catalin