From nobody Sun Feb 8 04:12:46 2026 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 DD4DDEB64DB for ; Mon, 19 Jun 2023 08:42:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230211AbjFSImi (ORCPT ); Mon, 19 Jun 2023 04:42:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229481AbjFSImR (ORCPT ); Mon, 19 Jun 2023 04:42:17 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9085126A1; Mon, 19 Jun 2023 01:40:06 -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 DEF242F4; Mon, 19 Jun 2023 01:39:27 -0700 (PDT) Received: from a077209.blr.arm.com (a077209.arm.com [10.162.43.124]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 6C4B53F64C; Mon, 19 Jun 2023 01:38:41 -0700 (PDT) From: Chaitanya S Prakash To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Anshuman.Khandual@arm.com, Chaitanya S Prakash , Catalin Marinas , Will Deacon , Jonathan Corbet , linux-doc@vger.kernel.org Subject: [PATCH V2] Documentation/arm64: Add ptdump documentation Date: Mon, 19 Jun 2023 14:08:02 +0530 Message-Id: <20230619083802.76092-1-chaitanyas.prakash@arm.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Changes in V2: - Corrected command to cat /sys/kernel/debug/kernel_page_tables Changes in V1: https://lore.kernel.org/all/20230613064845.1882177-1-chaitanyas.prakash@arm= .com/ 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..c7689d14e744 --- /dev/null +++ b/Documentation/arm64/ptdump.rst @@ -0,0 +1,94 @@ +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Kernel page table dump +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +ptdump is a debugfs interface that provides a detailed dump of the kernel's +page tables. It offers a comprehensive overview of the kernel=E2=80=99s vi= rtual +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=3Dy + CONFIG_PTDUMP_CORE=3Dy + CONFIG_PTDUMP_DEBUGFS=3Dy + + 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 +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 permission= s, +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:: + + 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_tables:: + + 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 --=20 2.25.1