1 .. SPDX-License-Identifier: GPL-2.0
2
3 ============================================================
4 Provoking crashes with Linux Kernel Dump Test Module (LKDTM)
5 ============================================================
6
7 The lkdtm module provides an interface to disrupt (and usually crash)
8 the kernel at predefined code locations to evaluate the reliability of
9 the kernel's exception handling and to test crash dumps obtained using
10 different dumping solutions. The module uses KPROBEs to instrument the
11 trigger location, but can also trigger the kernel directly without KPROBE
12 support via debugfs.
13
14 You can select the location of the trigger ("crash point name") and the
15 type of action ("crash point type") either through module arguments when
16 inserting the module, or through the debugfs interface.
17
18 Usage::
19
20 insmod lkdtm.ko [recur_count={>0}] cpoint_name=<> cpoint_type=<>
21 [cpoint_count={>0}]
22
23 recur_count
24 Recursion level for the stack overflow test. By default this is
25 dynamically calculated based on kernel configuration, with the
26 goal of being just large enough to exhaust the kernel stack. The
27 value can be seen at `/sys/module/lkdtm/parameters/recur_count`.
28
29 cpoint_name
30 Where in the kernel to trigger the action. It can be
31 one of INT_HARDWARE_ENTRY, INT_HW_IRQ_EN, INT_TASKLET_ENTRY,
32 FS_SUBMIT_BH, MEM_SWAPOUT, TIMERADD, SCSI_QUEUE_RQ, or DIRECT.
33
34 cpoint_type
35 Indicates the action to be taken on hitting the crash point.
36 These are numerous, and best queried directly from debugfs. Some
37 of the common ones are PANIC, BUG, EXCEPTION, LOOP, and OVERFLOW.
38 See the contents of `/sys/kernel/debug/provoke-crash/DIRECT` for
39 a complete list.
40
41 cpoint_count
42 Indicates the number of times the crash point is to be hit
43 before triggering the action. The default is 10 (except for
44 DIRECT, which always fires immediately).
45
46 You can also induce failures by mounting debugfs and writing the type to
47 <debugfs>/provoke-crash/<crashpoint>. E.g.::
48
49 mount -t debugfs debugfs /sys/kernel/debug
50 echo EXCEPTION > /sys/kernel/debug/provoke-crash/INT_HARDWARE_ENTRY
51
52 The special file `DIRECT` will induce the action directly without KPROBE
53 instrumentation. This mode is the only one available when the module is
54 built for a kernel without KPROBEs support::
55
56 # Instead of having a BUG kill your shell, have it kill "cat":
57 cat <(echo WRITE_RO) >/sys/kernel/debug/provoke-crash/DIRECT
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