From: Chaitanya S Prakash <chaitanyas.prakash@arm.com>
To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc: Anshuman.Khandual@arm.com,
Chaitanya S Prakash <chaitanyas.prakash@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
linux-doc@vger.kernel.org
Subject: [PATCH V2] Documentation/arm64: Add ptdump documentation
Date: Mon, 19 Jun 2023 14:08:02 +0530 [thread overview]
Message-ID: <20230619083802.76092-1-chaitanyas.prakash@arm.com> (raw)
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 <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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 <chaitanyas.prakash@arm.com>
---
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 @@
+======================
+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
+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::
+
+ 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
--
2.25.1
next reply other threads:[~2023-06-19 8:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-19 8:38 Chaitanya S Prakash [this message]
2023-06-21 15:49 ` [PATCH V2] Documentation/arm64: Add ptdump documentation Catalin Marinas
2023-06-21 16:04 ` Jonathan Corbet
2023-06-22 7:51 ` Catalin Marinas
2023-06-23 19:29 ` Jonathan Corbet
2023-06-23 20:32 ` Catalin Marinas
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20230619083802.76092-1-chaitanyas.prakash@arm.com \
--to=chaitanyas.prakash@arm.com \
--cc=Anshuman.Khandual@arm.com \
--cc=catalin.marinas@arm.com \
--cc=corbet@lwn.net \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).