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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 681C1EB64D8 for ; Wed, 14 Jun 2023 06:10:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243027AbjFNGKV (ORCPT ); Wed, 14 Jun 2023 02:10:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34566 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234205AbjFNGKS (ORCPT ); Wed, 14 Jun 2023 02:10:18 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 19DC9E55 for ; Tue, 13 Jun 2023 23:10:17 -0700 (PDT) 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 54E571FB; Tue, 13 Jun 2023 23:11:01 -0700 (PDT) Received: from [10.162.42.149] (a077209.arm.com [10.162.42.149]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2D9093F71E; Tue, 13 Jun 2023 23:10:14 -0700 (PDT) Message-ID: <7364a4fd-e1ad-9003-2a89-deb0c23c0edf@arm.com> Date: Wed, 14 Jun 2023 11:40:11 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH] Documentation/arm64: Add ptdump documentation To: Randy Dunlap , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, Anshuman.Khandual@arm.com References: <20230613064845.1882177-1-chaitanyas.prakash@arm.com> <5e003504-8224-8441-c1d5-a4e3327bdcc8@infradead.org> Content-Language: en-US From: Chaitanya S Prakash In-Reply-To: <5e003504-8224-8441-c1d5-a4e3327bdcc8@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/14/23 04:34, Randy Dunlap wrote: > Hi-- > > On 6/12/23 23:48, Chaitanya S Prakash wrote: >> ptdump is a debugfs interface used to dump the kernel page tables. It >> provides a comprehensive overview about the kernel's virtual memory >> layout, page table entries and associated page attributes. A document >> detailing how to enable ptdump in the kernel and analyse its output has >> been added. >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Jonathan Corbet >> CC: linux-arm-kernel@lists.infradead.org >> Cc: linux-doc@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Chaitanya S Prakash >> --- >> Documentation/arm64/index.rst | 1 + >> Documentation/arm64/ptdump.rst | 94 ++++++++++++++++++++++++++++++++++ >> 2 files changed, 95 insertions(+) >> create mode 100644 Documentation/arm64/ptdump.rst >> >> diff --git a/Documentation/arm64/index.rst b/Documentation/arm64/index.rst >> index ae21f8118830..e0bda3ec2090 100644 >> --- a/Documentation/arm64/index.rst >> +++ b/Documentation/arm64/index.rst >> @@ -15,6 +15,7 @@ ARM64 Architecture >> cpu-feature-registers >> elf_hwcaps >> hugetlbpage >> + ptdump >> legacy_instructions >> memory >> memory-tagging-extension >> diff --git a/Documentation/arm64/ptdump.rst b/Documentation/arm64/ptdump.rst >> new file mode 100644 >> index 000000000000..296a5fe217b0 >> --- /dev/null >> +++ b/Documentation/arm64/ptdump.rst >> @@ -0,0 +1,94 @@ >> +====================== >> +Kernel page table dump >> +====================== >> + >> +ptdump is a debugfs interface that provides a detailed dump of the kernel's >> +page tables. It offers a comprehensive overview of the kernel’s virtual >> +memory layout as well as the attributes associated with the various regions >> +in a human-readable format. It is useful to dump the kernel page tables to >> +verify permissions and memory types. Examining the page table entries and >> +permissions helps identify potential security vulnerabilities such as >> +mappings with overly permissive access rights or improper memory >> +protections. >> + >> +Memory hotplug allows dynamic expansion or contraction of available memory >> +without requiring a system reboot. To maintain consistency and integrity of >> +memory management data structures, arm64 makes use of mem_hotplug_lock in >> +write mode. Additionally, in read mode mem_hotplug_lock supports efficient >> +implementation of get_online_mems and put_online_mems. This protects the >> +offlining of memory being accessed by code. >> + >> +In order to dump the kernel page tables you will need to have the following >> +configurations enabled and follow it up by mounting debugfs.:: >> + >> + CONFIG_GENERIC_PTDUMP=y >> + CONFIG_PTDUMP_CORE=y >> + CONFIG_PTDUMP_DEBUGFS=y >> + >> + mount -t debugfs nodev /sys/kernel/debug >> + cat /sys/kernel/debug/kernel_page_tables >> + >> +On analysing the output of cat /sys/kernel/debug/kernel_page_tables you can > > Preferably quote the command. > This says kernel_page_tables but below it is 'kernel_page_table'. > Which is correct? The correct command is cat /sys/kernel/debug/kernel_page_tables. Sorry for the confusion! I'll correct the one below. > >> +derive information about the virtual address range of the entry, followed >> +by size of the memory region covered by this entry, the hierarchical >> +structure of the page tables and finally the attributes associated with >> +each page. The page attributes provide information about access permissions, >> +execution capability, type of mapping such as leaf level PTE or block level >> +PGD, PMD and PUD, and access status of a page within the kernel memory. >> +Assessing these attributes can assist in understanding the memory layout, >> +access patterns, and security characteristics of the kernel pages. >> + >> +Kernel virtual memory layout:: >> + > > Is this memory layout arm64-specific or generic? Yes, it's arm64-specific > >> + start address end address size attributes >> + +---------------------------------------------------------------------------------------+ >> + | ---[ Linear Mapping start ]---------------------------------------------------------- | >> + | .................. | >> + | 0xfff0000000000000-0xfff0000000210000 2112K PTE RW NX SHD AF UXN MEM/NORMAL-TAGGED | >> + | 0xfff0000000210000-0xfff0000001c00000 26560K PTE ro NX SHD AF UXN MEM/NORMAL | >> + | .................. | >> + | ---[ Linear Mapping end ]------------------------------------------------------------ | >> + +---------------------------------------------------------------------------------------+ >> + | ---[ Modules start ]----------------------------------------------------------------- | >> + | .................. | >> + | 0xffff800000000000-0xffff800008000000 128M PTE | >> + | .................. | >> + | ---[ Modules end ]------------------------------------------------------------------- | >> + +---------------------------------------------------------------------------------------+ >> + | ---[ vmalloc() area ]---------------------------------------------------------------- | >> + | .................. | >> + | 0xffff800008010000-0xffff800008200000 1984K PTE ro x SHD AF UXN MEM/NORMAL | >> + | 0xffff800008200000-0xffff800008e00000 12M PTE ro x SHD AF CON UXN MEM/NORMAL | >> + | .................. | >> + | ---[ vmalloc() end ]----------------------------------------------------------------- | >> + +---------------------------------------------------------------------------------------+ >> + | ---[ Fixmap start ]------------------------------------------------------------------ | >> + | .................. | >> + | 0xfffffbfffdb80000-0xfffffbfffdb90000 64K PTE ro x SHD AF UXN MEM/NORMAL | >> + | 0xfffffbfffdb90000-0xfffffbfffdba0000 64K PTE ro NX SHD AF UXN MEM/NORMAL | >> + | .................. | >> + | ---[ Fixmap end ]-------------------------------------------------------------------- | >> + +---------------------------------------------------------------------------------------+ >> + | ---[ PCI I/O start ]----------------------------------------------------------------- | >> + | .................. | >> + | 0xfffffbfffe800000-0xfffffbffff800000 16M PTE | >> + | .................. | >> + | ---[ PCI I/O end ]------------------------------------------------------------------- | >> + +---------------------------------------------------------------------------------------+ >> + | ---[ vmemmap start ]----------------------------------------------------------------- | >> + | .................. | >> + | 0xfffffc0002000000-0xfffffc0002200000 2M PTE RW NX SHD AF UXN MEM/NORMAL | >> + | 0xfffffc0002200000-0xfffffc0020000000 478M PTE | >> + | .................. | >> + | ---[ vmemmap end ]------------------------------------------------------------------- | >> + +---------------------------------------------------------------------------------------+ >> + >> +cat /sys/kernel/debug/kernel_page_table:: >> + >> + 0xfff0000001c00000-0xfff0000080000000 2020M PTE RW NX SHD AF UXN MEM/NORMAL-TAGGED >> + 0xfff0000080000000-0xfff0000800000000 30G PMD >> + 0xfff0000800000000-0xfff0000800700000 7M PTE RW NX SHD AF UXN MEM/NORMAL-TAGGED >> + 0xfff0000800700000-0xfff0000800710000 64K PTE ro NX SHD AF UXN MEM/NORMAL-TAGGED >> + 0xfff0000800710000-0xfff0000880000000 2089920K PTE RW NX SHD AF UXN MEM/NORMAL-TAGGED >> + 0xfff0000880000000-0xfff0040000000000 4062G PMD >> + 0xfff0040000000000-0xffff800000000000 3964T PGD > > thanks.