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 D00F4C04EBE for ; Thu, 8 Oct 2020 10:45:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 84A0721734 for ; Thu, 8 Oct 2020 10:45:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729539AbgJHKpN (ORCPT ); Thu, 8 Oct 2020 06:45:13 -0400 Received: from foss.arm.com ([217.140.110.172]:50036 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726766AbgJHKpM (ORCPT ); Thu, 8 Oct 2020 06:45:12 -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 21CCBD6E; Thu, 8 Oct 2020 03:45:11 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.52.79]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1EBF83F70D; Thu, 8 Oct 2020 03:45:03 -0700 (PDT) Date: Thu, 8 Oct 2020 11:45:01 +0100 From: Mark Rutland To: Marco Elver Cc: Alexander Potapenko , Will Deacon , Andrew Morton , "H. Peter Anvin" , "Paul E. McKenney" , Andrey Konovalov , Andrey Ryabinin , Andy Lutomirski , Borislav Petkov , Catalin Marinas , Christoph Lameter , Dave Hansen , David Rientjes , Dmitriy Vyukov , Eric Dumazet , Greg Kroah-Hartman , Hillf Danton , Ingo Molnar , Jann Horn , Jonathan Cameron , Jonathan Corbet , Joonsoo Kim , Kees Cook , Pekka Enberg , Peter Zijlstra , SeongJae Park , Thomas Gleixner , Vlastimil Babka , the arch/x86 maintainers , "open list:DOCUMENTATION" , LKML , kasan-dev , Linux ARM , Linux Memory Management List Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64 Message-ID: <20201008104501.GB72325@C02TD0UTHF1T.local> References: <20200921132611.1700350-1-elver@google.com> <20200921132611.1700350-4-elver@google.com> <20200921143059.GO2139@willie-the-truck> <20200929140226.GB53442@C02TD0UTHF1T.local> <20201001175716.GA89689@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 08, 2020 at 11:40:52AM +0200, Marco Elver wrote: > On Thu, 1 Oct 2020 at 19:58, Mark Rutland wrote: > [...] > > > > If you need virt_to_page() to work, the address has to be part of the > > > > linear/direct map. > [...] > > > > What's the underlying requirement here? Is this a performance concern, > > codegen/codesize, or something else? > > It used to be performance, since is_kfence_address() is used in the > fast path. However, with some further tweaks we just did to > is_kfence_address(), our benchmarks show a pointer load can be > tolerated. Great! I reckon that this is something we can optimize in futue if necessary (e.g. with some form of code-patching for immediate values), but it's good to have a starting point that works everywhere! [...] > > I'm not too worried about allocating this dynamically, but: > > > > * The arch code needs to set up the translation tables for this, as we > > cannot safely change the mapping granularity live. > > > > * As above I'm fairly certain x86 needs to use a carevout from the > > linear map to function correctly anyhow, so we should follow the same > > approach for both arm64 and x86. That might be a static carevout that > > we figure out the aliasing for, or something entirely dynamic. > > We're going with dynamically allocating the pool (for both x86 and > arm64), since any benefits we used to measure from the static pool are > no longer measurable (after removing a branch from > is_kfence_address()). It should hopefully simplify a lot of things, > given all the caveats that you pointed out. > > For arm64, the only thing left then is to fix up the case if the > linear map is not forced to page granularity. The simplest way to do this is to modify arm64's arch_add_memory() to force the entire linear map to be mapped at page granularity when KFENCE is enabled, something like: | diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c | index 936c4762dadff..f6eba0642a4a3 100644 | --- a/arch/arm64/mm/mmu.c | +++ b/arch/arm64/mm/mmu.c | @@ -1454,7 +1454,8 @@ int arch_add_memory(int nid, u64 start, u64 size, | { | int ret, flags = 0; | | - if (rodata_full || debug_pagealloc_enabled()) | + if (rodata_full || debug_pagealloc_enabled() || | + IS_ENABLED(CONFIG_KFENCE)) | flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; | | __create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start), ... and I given that RODATA_FULL_DEFAULT_ENABLED is the default, I suspect it's not worth trying to only for that for the KFENCE region unless someone complains. Thanks, Mark. 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=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 330C0C43467 for ; Thu, 8 Oct 2020 10:46:45 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 B6E7B21775 for ; Thu, 8 Oct 2020 10:46:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="m97DcRns" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B6E7B21775 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=merlin.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=z45iscPEq/Td9iqA7ALqbo6YfivjTgz6quNdZbA01ic=; b=m97DcRnsF3hDRLQjnvbgSjotO xyWB8RkLMJ0JJTEW5z2cljXsp6pyppuuUG9i+umuaIr6yKP/Bs++Lg+PpQOADl67MNGOLlmafDQgF +Ih/qx/mUkkYfP/AxHpPfawCGUm0ASAU/GCDAL/AMQ02rqj+i1rDlT/FPXXcpYAHuelWc9G1RWQ1T RBOA9WDpcYMZLgo1Fby6MlZ8OdNjX2uzpZDuBwtjrZvLKN0BzU0m2opgfo4EVFXJRwtTzyvBGTAHj JKoIxVd8W29mfU+F/MwVY4trfTPDg98rQ6w17zw5Vva9jA7QUSg+pqH2Tj2a/pg8FWBWimDJ8w6hq w71bPO7dA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kQTQA-0004xL-QB; Thu, 08 Oct 2020 10:45:14 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kQTQ8-0004wf-7w for linux-arm-kernel@lists.infradead.org; Thu, 08 Oct 2020 10:45:13 +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 21CCBD6E; Thu, 8 Oct 2020 03:45:11 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.52.79]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1EBF83F70D; Thu, 8 Oct 2020 03:45:03 -0700 (PDT) Date: Thu, 8 Oct 2020 11:45:01 +0100 From: Mark Rutland To: Marco Elver Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64 Message-ID: <20201008104501.GB72325@C02TD0UTHF1T.local> References: <20200921132611.1700350-1-elver@google.com> <20200921132611.1700350-4-elver@google.com> <20200921143059.GO2139@willie-the-truck> <20200929140226.GB53442@C02TD0UTHF1T.local> <20201001175716.GA89689@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201008_064512_375928_A8B711B1 X-CRM114-Status: GOOD ( 31.73 ) 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: Hillf Danton , "open list:DOCUMENTATION" , Peter Zijlstra , Catalin Marinas , Dave Hansen , Linux Memory Management List , Eric Dumazet , Alexander Potapenko , "H. Peter Anvin" , Christoph Lameter , Will Deacon , SeongJae Park , Jonathan Corbet , the arch/x86 maintainers , kasan-dev , Ingo Molnar , Vlastimil Babka , David Rientjes , Andrey Ryabinin , Kees Cook , "Paul E. McKenney" , Jann Horn , Andrey Konovalov , Borislav Petkov , Andy Lutomirski , Jonathan Cameron , Thomas Gleixner , Andrew Morton , Dmitriy Vyukov , Linux ARM , Greg Kroah-Hartman , LKML , Pekka Enberg , Joonsoo Kim Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 08, 2020 at 11:40:52AM +0200, Marco Elver wrote: > On Thu, 1 Oct 2020 at 19:58, Mark Rutland wrote: > [...] > > > > If you need virt_to_page() to work, the address has to be part of the > > > > linear/direct map. > [...] > > > > What's the underlying requirement here? Is this a performance concern, > > codegen/codesize, or something else? > > It used to be performance, since is_kfence_address() is used in the > fast path. However, with some further tweaks we just did to > is_kfence_address(), our benchmarks show a pointer load can be > tolerated. Great! I reckon that this is something we can optimize in futue if necessary (e.g. with some form of code-patching for immediate values), but it's good to have a starting point that works everywhere! [...] > > I'm not too worried about allocating this dynamically, but: > > > > * The arch code needs to set up the translation tables for this, as we > > cannot safely change the mapping granularity live. > > > > * As above I'm fairly certain x86 needs to use a carevout from the > > linear map to function correctly anyhow, so we should follow the same > > approach for both arm64 and x86. That might be a static carevout that > > we figure out the aliasing for, or something entirely dynamic. > > We're going with dynamically allocating the pool (for both x86 and > arm64), since any benefits we used to measure from the static pool are > no longer measurable (after removing a branch from > is_kfence_address()). It should hopefully simplify a lot of things, > given all the caveats that you pointed out. > > For arm64, the only thing left then is to fix up the case if the > linear map is not forced to page granularity. The simplest way to do this is to modify arm64's arch_add_memory() to force the entire linear map to be mapped at page granularity when KFENCE is enabled, something like: | diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c | index 936c4762dadff..f6eba0642a4a3 100644 | --- a/arch/arm64/mm/mmu.c | +++ b/arch/arm64/mm/mmu.c | @@ -1454,7 +1454,8 @@ int arch_add_memory(int nid, u64 start, u64 size, | { | int ret, flags = 0; | | - if (rodata_full || debug_pagealloc_enabled()) | + if (rodata_full || debug_pagealloc_enabled() || | + IS_ENABLED(CONFIG_KFENCE)) | flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; | | __create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start), ... and I given that RODATA_FULL_DEFAULT_ENABLED is the default, I suspect it's not worth trying to only for that for the KFENCE region unless someone complains. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel