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diff --git a/Documentation/arch/arm64/ptdump.rst b/Documentation/arch/arm64/ptdump.rst new file mode 100644 index 0000000000..5dcfc5d7cd --- /dev/null +++ b/Documentation/arch/arm64/ptdump.rst @@ -0,0 +1,96 @@ +====================== +Kernel page table dump +====================== + +ptdump is a debugfs interface that provides a detailed dump of the +kernel page tables. It offers a comprehensive overview of the kernel +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 the consistency +and integrity of the memory management data structures, arm64 makes use +of the ``mem_hotplug_lock`` semaphore in write mode. Additionally, in +read mode, ``mem_hotplug_lock`` supports an efficient implementation of +``get_online_mems()`` and ``put_online_mems()``. These protect the +offlining of memory being accessed by the ptdump code. + +In order to dump the kernel page tables, enable the following +configurations and mount 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`` +one 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 example:: + + 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`` output:: + + 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 |