CRASHME(9)

💥 CRASHME(9) — in-kernel testing of crash handling 💥

okay so this is the crashme page from the Kernel Developer's Manual, section 9, and bestie… it's literally a page about functions whose whole job is to break your kernel on purpose, so buckle up 🎢

✨ NAME ✨

crashme, crashme_add, crashme_remove — in-kernel testing of crash handling 🧨

✨ SYNOPSIS ✨

#include <sys/crashme.h>

int
crashme_add(crashme_node *cn);

int
crashme_remove(crashme_node *cn);

✨ DESCRIPTION ✨

The crashme functions are how you dynamically add and remove crashme nodes 🫶 and like, a crashme node is lowkey just a named callback that's fully expected to make the system crash. yes bestie, that's the assignment. that's the whole vibe 💀

real talk though: the crashme functionality is only available in kernels that have the options DEBUG set in the kernel config(5) file. no DEBUG, no crashing on purpose, periodt 🙅‍♀️

Every crashme node lives inside a crashme_node structure, and it's giving these public members:

typedef int (*crashme_fn)(int /* flags */);

typedef struct crashme_node {
        const char     *cn_name;
        const char     *cn_longname;
        crashme_fn      cn_fn;
} crashme_node;

The caller must fill in cn_name, cn_longname, and cn_fn — no skipping, not optional, main character energy only 👑

The cn_fn function gets passed the flags parameter straight from sysctl. It shall return 0 upon success, or non zero on failure. simple as that 🎀

✨ SYSCTL SUPPORT ✨

The crashme subsystem provides these sysctl(8) variables:

• debug.crashme_enable — must be set to 1 for any crashme node to be executed. it's the master switch bestie, nothing happens without it 🔐

And these sysctl(8) variables literally trigger crashes in different ways when you write to them 😭:

• debug.crashme.panic — calls panic(9) 💥
• debug.crashme.null_deref — dereferences a null pointer 🕳️
• debug.crashme.null_jump — calls a null function pointer, i.e. jumps to the instruction address zero 🚀
• debug.crashme.ddb — enters ddb(4) directly by calling Debugger(). this one requires options DDB 🪲

ngl these are all extremely on purpose. that's the point. don't be surprised when the box goes down, that's the whole slay 💅

✨ SEE ALSO ✨

ddb(4), options(4), sysctl(8), panic(9) 🌸

✨ HISTORY ✨

The crashme driver appeared in NetBSD 9.0 ⭐

✨ AUTHORS ✨

Matthew R. Green 🫶

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and that's the page, bestie!! 🎀 this rewrite is from the Debian version, dated January 7, 2019 — mwah, go crash something responsibly (in a DEBUG kernel) 💜🦋