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=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 A5B46CA9EA0 for ; Fri, 18 Oct 2019 13:37:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 86C85222C3 for ; Fri, 18 Oct 2019 13:37:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2410389AbfJRNhD (ORCPT ); Fri, 18 Oct 2019 09:37:03 -0400 Received: from [217.140.110.172] ([217.140.110.172]:39522 "EHLO foss.arm.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1728150AbfJRNhC (ORCPT ); Fri, 18 Oct 2019 09:37:02 -0400 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 A62E03BB; Fri, 18 Oct 2019 06:36:39 -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 BBC903F6C4; Fri, 18 Oct 2019 06:36:36 -0700 (PDT) Date: Fri, 18 Oct 2019 14:36:34 +0100 From: Dave Martin To: Mark Rutland Cc: Paul Elliott , Peter Zijlstra , Catalin Marinas , Will Deacon , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , linux-arch@vger.kernel.org, Eugene Syromiatnikov , Szabolcs Nagy , "H.J. Lu" , Andrew Jones , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Mark Brown , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Florian Weimer , linux-kernel@vger.kernel.org, Sudakshina Das Subject: Re: [PATCH v2 05/12] arm64: Basic Branch Target Identification support Message-ID: <20191018133628.GC27757@arm.com> References: <1570733080-21015-1-git-send-email-Dave.Martin@arm.com> <1570733080-21015-6-git-send-email-Dave.Martin@arm.com> <20191011151028.GE33537@lakrids.cambridge.arm.com> <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> <20191011153225.GL27757@arm.com> <20191011154043.GG33537@lakrids.cambridge.arm.com> <20191011154444.GN27757@arm.com> <20191011160113.GO27757@arm.com> <20191011164159.GP27757@arm.com> <20191018110551.GB27759@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191018110551.GB27759@lakrids.cambridge.arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 18, 2019 at 12:05:52PM +0100, Mark Rutland wrote: > On Fri, Oct 11, 2019 at 05:42:00PM +0100, Dave Martin wrote: > > On Fri, Oct 11, 2019 at 05:01:13PM +0100, Dave Martin wrote: > > > On Fri, Oct 11, 2019 at 04:44:45PM +0100, Dave Martin wrote: > > > > On Fri, Oct 11, 2019 at 04:40:43PM +0100, Mark Rutland wrote: > > > > > On Fri, Oct 11, 2019 at 04:32:26PM +0100, Dave Martin wrote: [...] > > > > > > Either way, I feel we should do this: any function in a PROT_BTI page > > > > > > should have a suitable landing pad. There's no reason I can see why > > > > > > a protection given to any other callback function should be omitted > > > > > > for a signal handler. > > > > > > > > > > > > Note, if the signal handler isn't in a PROT_BTI page then overriding > > > > > > BTYPE here will not trigger a Branch Target exception. > > > > > > > > > > > > I'm happy to drop a brief comment into the code also, once we're > > > > > > agreed on what the code should be doing. > > > > > > > > > > So long as there's a comment as to why, I have no strong feelings here. > > > > > :) > > > > > > > > OK, I think it's worth a brief comment in the code either way, so I'll > > > > add something. > > > > > > Hmm, come to think of it we do need special logic for a particular case > > > here: > > > > > > If we are delivering a SIGILL here and the SIGILL handler was registered > > > with SA_NODEFER then we will get into a spin, repeatedly delivering > > > the BTI-triggered SIGILL to the same (bad) entry point. > > > > > > Without SA_NODEFER, the SIGILL becomes fatal, which is the desired > > > behaviour, but we'll need to catch this recursion explicitly. > > > > > > > > > It's similar to the special force_sigsegv() case in > > > linux/kernel/signal.c... > > > > > > Thoughts? > > > > On second thought, maybe we don't need to do anything special. > > > > A SIGSEGV handler registered with (SA_NODEFER & ~SA_RESETHAND) and that > > dereferences a duff address would spin similarly. > > > > This SIGILL case doesn't really seem different. Either way it's a > > livelock of the user task that doesn't compromise the kernel. There > > are plenty of ways for such a livelock to happen. > > That sounds reasonable to me. OK, I guess we can park this discussion for now. Cheers ---Dave From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Martin Subject: Re: [PATCH v2 05/12] arm64: Basic Branch Target Identification support Date: Fri, 18 Oct 2019 14:36:34 +0100 Message-ID: <20191018133628.GC27757@arm.com> References: <1570733080-21015-1-git-send-email-Dave.Martin@arm.com> <1570733080-21015-6-git-send-email-Dave.Martin@arm.com> <20191011151028.GE33537@lakrids.cambridge.arm.com> <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> <20191011153225.GL27757@arm.com> <20191011154043.GG33537@lakrids.cambridge.arm.com> <20191011154444.GN27757@arm.com> <20191011160113.GO27757@arm.com> <20191011164159.GP27757@arm.com> <20191018110551.GB27759@lakrids.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20191018110551.GB27759@lakrids.cambridge.arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Mark Rutland Cc: Paul Elliott , Peter Zijlstra , Catalin Marinas , Will Deacon , Andrew Jones , Amit Kachhap , Vincenzo Frascino , linux-arch@vger.kernel.org, Eugene Syromiatnikov , Szabolcs Nagy , "H.J. Lu" , Yu-cheng Yu , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Mark Brown , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Florian Weimer , linux-kernel@vger.kernel.org, Sudakshina Das List-Id: linux-arch.vger.kernel.org On Fri, Oct 18, 2019 at 12:05:52PM +0100, Mark Rutland wrote: > On Fri, Oct 11, 2019 at 05:42:00PM +0100, Dave Martin wrote: > > On Fri, Oct 11, 2019 at 05:01:13PM +0100, Dave Martin wrote: > > > On Fri, Oct 11, 2019 at 04:44:45PM +0100, Dave Martin wrote: > > > > On Fri, Oct 11, 2019 at 04:40:43PM +0100, Mark Rutland wrote: > > > > > On Fri, Oct 11, 2019 at 04:32:26PM +0100, Dave Martin wrote: [...] > > > > > > Either way, I feel we should do this: any function in a PROT_BTI page > > > > > > should have a suitable landing pad. There's no reason I can see why > > > > > > a protection given to any other callback function should be omitted > > > > > > for a signal handler. > > > > > > > > > > > > Note, if the signal handler isn't in a PROT_BTI page then overriding > > > > > > BTYPE here will not trigger a Branch Target exception. > > > > > > > > > > > > I'm happy to drop a brief comment into the code also, once we're > > > > > > agreed on what the code should be doing. > > > > > > > > > > So long as there's a comment as to why, I have no strong feelings here. > > > > > :) > > > > > > > > OK, I think it's worth a brief comment in the code either way, so I'll > > > > add something. > > > > > > Hmm, come to think of it we do need special logic for a particular case > > > here: > > > > > > If we are delivering a SIGILL here and the SIGILL handler was registered > > > with SA_NODEFER then we will get into a spin, repeatedly delivering > > > the BTI-triggered SIGILL to the same (bad) entry point. > > > > > > Without SA_NODEFER, the SIGILL becomes fatal, which is the desired > > > behaviour, but we'll need to catch this recursion explicitly. > > > > > > > > > It's similar to the special force_sigsegv() case in > > > linux/kernel/signal.c... > > > > > > Thoughts? > > > > On second thought, maybe we don't need to do anything special. > > > > A SIGSEGV handler registered with (SA_NODEFER & ~SA_RESETHAND) and that > > dereferences a duff address would spin similarly. > > > > This SIGILL case doesn't really seem different. Either way it's a > > livelock of the user task that doesn't compromise the kernel. There > > are plenty of ways for such a livelock to happen. > > That sounds reasonable to me. OK, I guess we can park this discussion for now. Cheers ---Dave 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,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 C5525CA9EA1 for ; Fri, 18 Oct 2019 13:36:55 +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 9248F222C3 for ; Fri, 18 Oct 2019 13:36:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="u8yj6K7e" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9248F222C3 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=AKldxGZ3RC03q+Ve5WZquUVbQNMs0MaPMbbj6vQeuUk=; b=u8yj6K7enDJ7FF cX3aQyxMUSYqStW8vl4KWvJ16V8vLp5tWgvj+O5JYLZrA0x6vB+nbOgki6Z118m6FE6+Wpc+tg16N 3JMSk3LhlF5bN3wG8zfBAlGUctRsamfgBsOfqHxNWRuutVgVTQX1Kk6DIUfgz2XNfdupFoSEptNis uFmYnBBhQ5B36G4Ah12IRAo4bLF+QvNcN0WJ8JaJbfu6ynzv/ofbUD4NK6btW3kMsClChEVhKaaBJ Vn2yAfmlkNI7a56Tj0VvpU/vZAnQXQ//1uF1RaMzsIODt82OSp/IaAVaOWiOcaPwsPxPOQR080roQ m1Cm8mzShjoQo2qyuspA==; 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 1iLSR4-0006Pu-T1; Fri, 18 Oct 2019 13:36:54 +0000 Received: from [217.140.110.172] (helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1iLSR0-0006PL-Pz for linux-arm-kernel@lists.infradead.org; Fri, 18 Oct 2019 13:36:52 +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 A62E03BB; Fri, 18 Oct 2019 06:36:39 -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 BBC903F6C4; Fri, 18 Oct 2019 06:36:36 -0700 (PDT) Date: Fri, 18 Oct 2019 14:36:34 +0100 From: Dave Martin To: Mark Rutland Subject: Re: [PATCH v2 05/12] arm64: Basic Branch Target Identification support Message-ID: <20191018133628.GC27757@arm.com> References: <1570733080-21015-1-git-send-email-Dave.Martin@arm.com> <1570733080-21015-6-git-send-email-Dave.Martin@arm.com> <20191011151028.GE33537@lakrids.cambridge.arm.com> <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> <20191011153225.GL27757@arm.com> <20191011154043.GG33537@lakrids.cambridge.arm.com> <20191011154444.GN27757@arm.com> <20191011160113.GO27757@arm.com> <20191011164159.GP27757@arm.com> <20191018110551.GB27759@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20191018110551.GB27759@lakrids.cambridge.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-20191018_063650_932496_32A29407 X-CRM114-Status: GOOD ( 21.33 ) 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: Paul Elliott , Peter Zijlstra , Catalin Marinas , Will Deacon , Andrew Jones , Amit Kachhap , Vincenzo Frascino , linux-arch@vger.kernel.org, Eugene Syromiatnikov , Szabolcs Nagy , "H.J. Lu" , Yu-cheng Yu , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Mark Brown , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Florian Weimer , linux-kernel@vger.kernel.org, Sudakshina Das 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 Fri, Oct 18, 2019 at 12:05:52PM +0100, Mark Rutland wrote: > On Fri, Oct 11, 2019 at 05:42:00PM +0100, Dave Martin wrote: > > On Fri, Oct 11, 2019 at 05:01:13PM +0100, Dave Martin wrote: > > > On Fri, Oct 11, 2019 at 04:44:45PM +0100, Dave Martin wrote: > > > > On Fri, Oct 11, 2019 at 04:40:43PM +0100, Mark Rutland wrote: > > > > > On Fri, Oct 11, 2019 at 04:32:26PM +0100, Dave Martin wrote: [...] > > > > > > Either way, I feel we should do this: any function in a PROT_BTI page > > > > > > should have a suitable landing pad. There's no reason I can see why > > > > > > a protection given to any other callback function should be omitted > > > > > > for a signal handler. > > > > > > > > > > > > Note, if the signal handler isn't in a PROT_BTI page then overriding > > > > > > BTYPE here will not trigger a Branch Target exception. > > > > > > > > > > > > I'm happy to drop a brief comment into the code also, once we're > > > > > > agreed on what the code should be doing. > > > > > > > > > > So long as there's a comment as to why, I have no strong feelings here. > > > > > :) > > > > > > > > OK, I think it's worth a brief comment in the code either way, so I'll > > > > add something. > > > > > > Hmm, come to think of it we do need special logic for a particular case > > > here: > > > > > > If we are delivering a SIGILL here and the SIGILL handler was registered > > > with SA_NODEFER then we will get into a spin, repeatedly delivering > > > the BTI-triggered SIGILL to the same (bad) entry point. > > > > > > Without SA_NODEFER, the SIGILL becomes fatal, which is the desired > > > behaviour, but we'll need to catch this recursion explicitly. > > > > > > > > > It's similar to the special force_sigsegv() case in > > > linux/kernel/signal.c... > > > > > > Thoughts? > > > > On second thought, maybe we don't need to do anything special. > > > > A SIGSEGV handler registered with (SA_NODEFER & ~SA_RESETHAND) and that > > dereferences a duff address would spin similarly. > > > > This SIGILL case doesn't really seem different. Either way it's a > > livelock of the user task that doesn't compromise the kernel. There > > are plenty of ways for such a livelock to happen. > > That sounds reasonable to me. OK, I guess we can park this discussion for now. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel