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brings some order to the documentation directory, declutters the top-level directory, and makes the documentation organization more closely match that of the source. -----BEGIN PGP SIGNATURE----- iQFDBAABCAAtFiEEIw+MvkEiF49krdp9F0NaE2wMflgFAmSbDsIPHGNvcmJldEBs d24ubmV0AAoJEBdDWhNsDH5Y+ksH/2Xqun1ipPvu66+bBdPIf8N9AVFatl2q3mt4 tgX3A4RH3Ejklb4GbRLOIP23PmCxt7LRv4P05ttw8VpTP3A+Cw1d1s2RxiXGvfDE j7IW6hrpUmVoDdiDCRGtjdIa7MVI5aAsj8CCTjEFywGi5CQe0Uzq4aTUKoxJDEnu GYVy2CwDNEt4GTQ6ClPpFx2rc4UZf/H2XqXsnod9ef8A5Nkt3EtgoS1hh3o1QZGA Mqx2HAOVS1tb6GUVUbVLCdj40+YjBLjXFlsH4dA+wsFFdUlZLKuTesdiAMg2X6eT E8C/6oRT+OiWbrnXUTJEn8z98Ds8VHn7D4n97O9bIQ+R9AFtmPI= =H/+D -----END PGP SIGNATURE----- Merge tag 'docs-arm64-move' of git://git.lwn.net/linux Pull arm64 documentation move from Jonathan Corbet: "Move the arm64 architecture documentation under Documentation/arch/. This brings some order to the documentation directory, declutters the top-level directory, and makes the documentation organization more closely match that of the source" * tag 'docs-arm64-move' of git://git.lwn.net/linux: perf arm-spe: Fix a dangling Documentation/arm64 reference mm: Fix a dangling Documentation/arm64 reference arm64: Fix dangling references to Documentation/arm64 dt-bindings: fix dangling Documentation/arm64 reference docs: arm64: Move arm64 documentation under Documentation/arch/
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6.3 KiB
ReStructuredText
96 lines
6.3 KiB
ReStructuredText
======================
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Kernel page table dump
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======================
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ptdump is a debugfs interface that provides a detailed dump of the
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kernel page tables. It offers a comprehensive overview of the kernel
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virtual memory layout as well as the attributes associated with the
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various regions in a human-readable format. It is useful to dump the
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kernel page tables to verify permissions and memory types. Examining the
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page table entries and permissions helps identify potential security
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vulnerabilities such as mappings with overly permissive access rights or
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improper memory protections.
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Memory hotplug allows dynamic expansion or contraction of available
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memory without requiring a system reboot. To maintain the consistency
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and integrity of the memory management data structures, arm64 makes use
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of the ``mem_hotplug_lock`` semaphore in write mode. Additionally, in
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read mode, ``mem_hotplug_lock`` supports an efficient implementation of
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``get_online_mems()`` and ``put_online_mems()``. These protect the
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offlining of memory being accessed by the ptdump code.
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In order to dump the kernel page tables, enable the following
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configurations and mount debugfs::
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CONFIG_GENERIC_PTDUMP=y
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CONFIG_PTDUMP_CORE=y
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CONFIG_PTDUMP_DEBUGFS=y
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mount -t debugfs nodev /sys/kernel/debug
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cat /sys/kernel/debug/kernel_page_tables
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On analysing the output of ``cat /sys/kernel/debug/kernel_page_tables``
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one can derive information about the virtual address range of the entry,
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followed by size of the memory region covered by this entry, the
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hierarchical structure of the page tables and finally the attributes
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associated with each page. The page attributes provide information about
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access permissions, execution capability, type of mapping such as leaf
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level PTE or block level PGD, PMD and PUD, and access status of a page
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within the kernel memory. Assessing these attributes can assist in
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understanding the memory layout, access patterns and security
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characteristics of the kernel pages.
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Kernel virtual memory layout example::
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start address end address size attributes
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+---------------------------------------------------------------------------------------+
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| ---[ Linear Mapping start ]---------------------------------------------------------- |
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| .................. |
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| 0xfff0000000000000-0xfff0000000210000 2112K PTE RW NX SHD AF UXN MEM/NORMAL-TAGGED |
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| 0xfff0000000210000-0xfff0000001c00000 26560K PTE ro NX SHD AF UXN MEM/NORMAL |
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| .................. |
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| ---[ Linear Mapping end ]------------------------------------------------------------ |
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+---------------------------------------------------------------------------------------+
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| ---[ Modules start ]----------------------------------------------------------------- |
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| .................. |
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| 0xffff800000000000-0xffff800008000000 128M PTE |
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| .................. |
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| ---[ Modules end ]------------------------------------------------------------------- |
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+---------------------------------------------------------------------------------------+
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| ---[ vmalloc() area ]---------------------------------------------------------------- |
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| .................. |
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| 0xffff800008010000-0xffff800008200000 1984K PTE ro x SHD AF UXN MEM/NORMAL |
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| 0xffff800008200000-0xffff800008e00000 12M PTE ro x SHD AF CON UXN MEM/NORMAL |
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| .................. |
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| ---[ vmalloc() end ]----------------------------------------------------------------- |
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+---------------------------------------------------------------------------------------+
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| ---[ Fixmap start ]------------------------------------------------------------------ |
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| .................. |
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| 0xfffffbfffdb80000-0xfffffbfffdb90000 64K PTE ro x SHD AF UXN MEM/NORMAL |
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| 0xfffffbfffdb90000-0xfffffbfffdba0000 64K PTE ro NX SHD AF UXN MEM/NORMAL |
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| .................. |
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| ---[ Fixmap end ]-------------------------------------------------------------------- |
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+---------------------------------------------------------------------------------------+
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| ---[ PCI I/O start ]----------------------------------------------------------------- |
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| .................. |
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| 0xfffffbfffe800000-0xfffffbffff800000 16M PTE |
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| .................. |
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| ---[ PCI I/O end ]------------------------------------------------------------------- |
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+---------------------------------------------------------------------------------------+
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| ---[ vmemmap start ]----------------------------------------------------------------- |
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| .................. |
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| 0xfffffc0002000000-0xfffffc0002200000 2M PTE RW NX SHD AF UXN MEM/NORMAL |
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| 0xfffffc0002200000-0xfffffc0020000000 478M PTE |
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| .................. |
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| ---[ vmemmap end ]------------------------------------------------------------------- |
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+---------------------------------------------------------------------------------------+
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``cat /sys/kernel/debug/kernel_page_tables`` output::
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0xfff0000001c00000-0xfff0000080000000 2020M PTE RW NX SHD AF UXN MEM/NORMAL-TAGGED
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0xfff0000080000000-0xfff0000800000000 30G PMD
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0xfff0000800000000-0xfff0000800700000 7M PTE RW NX SHD AF UXN MEM/NORMAL-TAGGED
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0xfff0000800700000-0xfff0000800710000 64K PTE ro NX SHD AF UXN MEM/NORMAL-TAGGED
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0xfff0000800710000-0xfff0000880000000 2089920K PTE RW NX SHD AF UXN MEM/NORMAL-TAGGED
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0xfff0000880000000-0xfff0040000000000 4062G PMD
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0xfff0040000000000-0xffff800000000000 3964T PGD
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