1 ======================
2 Kernel page table dump
3 ======================
4
5 ptdump is a debugfs interface that provides a
6 kernel page tables. It offers a comprehensive
7 virtual memory layout as well as the attribute
8 various regions in a human-readable format. It
9 kernel page tables to verify permissions and m
10 page table entries and permissions helps ident
11 vulnerabilities such as mappings with overly p
12 improper memory protections.
13
14 Memory hotplug allows dynamic expansion or con
15 memory without requiring a system reboot. To m
16 and integrity of the memory management data st
17 of the ``mem_hotplug_lock`` semaphore in write
18 read mode, ``mem_hotplug_lock`` supports an ef
19 ``get_online_mems()`` and ``put_online_mems()`
20 offlining of memory being accessed by the ptdu
21
22 In order to dump the kernel page tables, enabl
23 configurations and mount debugfs::
24
25 CONFIG_GENERIC_PTDUMP=y
26 CONFIG_PTDUMP_CORE=y
27 CONFIG_PTDUMP_DEBUGFS=y
28
29 mount -t debugfs nodev /sys/kernel/debug
30 cat /sys/kernel/debug/kernel_page_tables
31
32 On analysing the output of ``cat /sys/kernel/d
33 one can derive information about the virtual a
34 followed by size of the memory region covered
35 hierarchical structure of the page tables and
36 associated with each page. The page attributes
37 access permissions, execution capability, type
38 level PTE or block level PGD, PMD and PUD, and
39 within the kernel memory. Assessing these attr
40 understanding the memory layout, access patter
41 characteristics of the kernel pages.
42
43 Kernel virtual memory layout example::
44
45 start address end address size
46 +--------------------------------------------
47 | ---[ Linear Mapping start ]----------------
48 | ..................
49 | 0xfff0000000000000-0xfff0000000210000 2112
50 | 0xfff0000000210000-0xfff0000001c00000 26560
51 | ..................
52 | ---[ Linear Mapping end ]------------------
53 +--------------------------------------------
54 | ---[ Modules start ]-----------------------
55 | ..................
56 | 0xffff800000000000-0xffff800008000000 128
57 | ..................
58 | ---[ Modules end ]-------------------------
59 +--------------------------------------------
60 | ---[ vmalloc() area ]----------------------
61 | ..................
62 | 0xffff800008010000-0xffff800008200000 1984
63 | 0xffff800008200000-0xffff800008e00000 12
64 | ..................
65 | ---[ vmalloc() end ]-----------------------
66 +--------------------------------------------
67 | ---[ Fixmap start ]------------------------
68 | ..................
69 | 0xfffffbfffdb80000-0xfffffbfffdb90000 64
70 | 0xfffffbfffdb90000-0xfffffbfffdba0000 64
71 | ..................
72 | ---[ Fixmap end ]--------------------------
73 +--------------------------------------------
74 | ---[ PCI I/O start ]-----------------------
75 | ..................
76 | 0xfffffbfffe800000-0xfffffbffff800000 16
77 | ..................
78 | ---[ PCI I/O end ]-------------------------
79 +--------------------------------------------
80 | ---[ vmemmap start ]-----------------------
81 | ..................
82 | 0xfffffc0002000000-0xfffffc0002200000 2
83 | 0xfffffc0002200000-0xfffffc0020000000 478
84 | ..................
85 | ---[ vmemmap end ]-------------------------
86 +--------------------------------------------
87
88 ``cat /sys/kernel/debug/kernel_page_tables`` o
89
90 0xfff0000001c00000-0xfff0000080000000 202
91 0xfff0000080000000-0xfff0000800000000 3
92 0xfff0000800000000-0xfff0000800700000
93 0xfff0000800700000-0xfff0000800710000 6
94 0xfff0000800710000-0xfff0000880000000 208992
95 0xfff0000880000000-0xfff0040000000000 406
96 0xfff0040000000000-0xffff800000000000 396
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