1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* |
3 | * KGDB NMI serial console |
4 | * |
5 | * Copyright 2010 Google, Inc. |
6 | * Arve Hjønnevåg <arve@android.com> |
7 | * Colin Cross <ccross@android.com> |
8 | * Copyright 2012 Linaro Ltd. |
9 | * Anton Vorontsov <anton.vorontsov@linaro.org> |
10 | */ |
11 | |
12 | #include <linux/kernel.h> |
13 | #include <linux/module.h> |
14 | #include <linux/compiler.h> |
15 | #include <linux/slab.h> |
16 | #include <linux/errno.h> |
17 | #include <linux/atomic.h> |
18 | #include <linux/console.h> |
19 | #include <linux/tty.h> |
20 | #include <linux/tty_driver.h> |
21 | #include <linux/tty_flip.h> |
22 | #include <linux/serial_core.h> |
23 | #include <linux/interrupt.h> |
24 | #include <linux/hrtimer.h> |
25 | #include <linux/tick.h> |
26 | #include <linux/kfifo.h> |
27 | #include <linux/kgdb.h> |
28 | #include <linux/kdb.h> |
29 | |
30 | static int kgdb_nmi_knock = 1; |
31 | module_param_named(knock, kgdb_nmi_knock, int, 0600); |
32 | MODULE_PARM_DESC(knock, "if set to 1 (default), the special '$3#33' command " \ |
33 | "must be used to enter the debugger; when set to 0, " \ |
34 | "hitting return key is enough to enter the debugger; " \ |
35 | "when set to -1, the debugger is entered immediately " \ |
36 | "upon NMI" ); |
37 | |
38 | static char *kgdb_nmi_magic = "$3#33" ; |
39 | module_param_named(magic, kgdb_nmi_magic, charp, 0600); |
40 | MODULE_PARM_DESC(magic, "magic sequence to enter NMI debugger (default $3#33)" ); |
41 | |
42 | static atomic_t kgdb_nmi_num_readers = ATOMIC_INIT(0); |
43 | |
44 | static int kgdb_nmi_console_setup(struct console *co, char *options) |
45 | { |
46 | arch_kgdb_ops.enable_nmi(1); |
47 | |
48 | /* The NMI console uses the dbg_io_ops to issue console messages. To |
49 | * avoid duplicate messages during kdb sessions we must inform kdb's |
50 | * I/O utilities that messages sent to the console will automatically |
51 | * be displayed on the dbg_io. |
52 | */ |
53 | dbg_io_ops->cons = co; |
54 | |
55 | return 0; |
56 | } |
57 | |
58 | static void kgdb_nmi_console_write(struct console *co, const char *s, uint c) |
59 | { |
60 | int i; |
61 | |
62 | for (i = 0; i < c; i++) |
63 | dbg_io_ops->write_char(s[i]); |
64 | } |
65 | |
66 | static struct tty_driver *kgdb_nmi_tty_driver; |
67 | |
68 | static struct tty_driver *kgdb_nmi_console_device(struct console *co, int *idx) |
69 | { |
70 | *idx = co->index; |
71 | return kgdb_nmi_tty_driver; |
72 | } |
73 | |
74 | static struct console kgdb_nmi_console = { |
75 | .name = "ttyNMI" , |
76 | .setup = kgdb_nmi_console_setup, |
77 | .write = kgdb_nmi_console_write, |
78 | .device = kgdb_nmi_console_device, |
79 | .flags = CON_PRINTBUFFER | CON_ANYTIME, |
80 | .index = -1, |
81 | }; |
82 | |
83 | /* |
84 | * This is usually the maximum rate on debug ports. We make fifo large enough |
85 | * to make copy-pasting to the terminal usable. |
86 | */ |
87 | #define KGDB_NMI_BAUD 115200 |
88 | #define KGDB_NMI_FIFO_SIZE roundup_pow_of_two(KGDB_NMI_BAUD / 8 / HZ) |
89 | |
90 | struct kgdb_nmi_tty_priv { |
91 | struct tty_port port; |
92 | struct timer_list timer; |
93 | STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo; |
94 | }; |
95 | |
96 | static struct tty_port *kgdb_nmi_port; |
97 | |
98 | static void kgdb_tty_recv(int ch) |
99 | { |
100 | struct kgdb_nmi_tty_priv *priv; |
101 | char c = ch; |
102 | |
103 | if (!kgdb_nmi_port || ch < 0) |
104 | return; |
105 | /* |
106 | * Can't use port->tty->driver_data as tty might be not there. Timer |
107 | * will check for tty and will get the ref, but here we don't have to |
108 | * do that, and actually, we can't: we're in NMI context, no locks are |
109 | * possible. |
110 | */ |
111 | priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port); |
112 | kfifo_in(&priv->fifo, &c, 1); |
113 | } |
114 | |
115 | static int kgdb_nmi_poll_one_knock(void) |
116 | { |
117 | static int n; |
118 | int c; |
119 | const char *magic = kgdb_nmi_magic; |
120 | size_t m = strlen(magic); |
121 | bool printch = false; |
122 | |
123 | c = dbg_io_ops->read_char(); |
124 | if (c == NO_POLL_CHAR) |
125 | return c; |
126 | |
127 | if (!kgdb_nmi_knock && (c == '\r' || c == '\n')) { |
128 | return 1; |
129 | } else if (c == magic[n]) { |
130 | n = (n + 1) % m; |
131 | if (!n) |
132 | return 1; |
133 | printch = true; |
134 | } else { |
135 | n = 0; |
136 | } |
137 | |
138 | if (atomic_read(v: &kgdb_nmi_num_readers)) { |
139 | kgdb_tty_recv(ch: c); |
140 | return 0; |
141 | } |
142 | |
143 | if (printch) { |
144 | kdb_printf("%c" , c); |
145 | return 0; |
146 | } |
147 | |
148 | kdb_printf("\r%s %s to enter the debugger> %*s" , |
149 | kgdb_nmi_knock ? "Type" : "Hit" , |
150 | kgdb_nmi_knock ? magic : "<return>" , (int)m, "" ); |
151 | while (m--) |
152 | kdb_printf("\b" ); |
153 | return 0; |
154 | } |
155 | |
156 | /** |
157 | * kgdb_nmi_poll_knock - Check if it is time to enter the debugger |
158 | * |
159 | * "Serial ports are often noisy, especially when muxed over another port (we |
160 | * often use serial over the headset connector). Noise on the async command |
161 | * line just causes characters that are ignored, on a command line that blocked |
162 | * execution noise would be catastrophic." -- Colin Cross |
163 | * |
164 | * So, this function implements KGDB/KDB knocking on the serial line: we won't |
165 | * enter the debugger until we receive a known magic phrase (which is actually |
166 | * "$3#33", known as "escape to KDB" command. There is also a relaxed variant |
167 | * of knocking, i.e. just pressing the return key is enough to enter the |
168 | * debugger. And if knocking is disabled, the function always returns 1. |
169 | */ |
170 | bool kgdb_nmi_poll_knock(void) |
171 | { |
172 | if (kgdb_nmi_knock < 0) |
173 | return true; |
174 | |
175 | while (1) { |
176 | int ret; |
177 | |
178 | ret = kgdb_nmi_poll_one_knock(); |
179 | if (ret == NO_POLL_CHAR) |
180 | return false; |
181 | else if (ret == 1) |
182 | break; |
183 | } |
184 | return true; |
185 | } |
186 | |
187 | /* |
188 | * The tasklet is cheap, it does not cause wakeups when reschedules itself, |
189 | * instead it waits for the next tick. |
190 | */ |
191 | static void kgdb_nmi_tty_receiver(struct timer_list *t) |
192 | { |
193 | struct kgdb_nmi_tty_priv *priv = from_timer(priv, t, timer); |
194 | char ch; |
195 | |
196 | priv->timer.expires = jiffies + (HZ/100); |
197 | add_timer(timer: &priv->timer); |
198 | |
199 | if (likely(!atomic_read(&kgdb_nmi_num_readers) || |
200 | !kfifo_len(&priv->fifo))) |
201 | return; |
202 | |
203 | while (kfifo_out(&priv->fifo, &ch, 1)) |
204 | tty_insert_flip_char(port: &priv->port, ch, TTY_NORMAL); |
205 | tty_flip_buffer_push(port: &priv->port); |
206 | } |
207 | |
208 | static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty) |
209 | { |
210 | struct kgdb_nmi_tty_priv *priv = |
211 | container_of(port, struct kgdb_nmi_tty_priv, port); |
212 | |
213 | kgdb_nmi_port = port; |
214 | priv->timer.expires = jiffies + (HZ/100); |
215 | add_timer(timer: &priv->timer); |
216 | |
217 | return 0; |
218 | } |
219 | |
220 | static void kgdb_nmi_tty_shutdown(struct tty_port *port) |
221 | { |
222 | struct kgdb_nmi_tty_priv *priv = |
223 | container_of(port, struct kgdb_nmi_tty_priv, port); |
224 | |
225 | del_timer(timer: &priv->timer); |
226 | kgdb_nmi_port = NULL; |
227 | } |
228 | |
229 | static const struct tty_port_operations kgdb_nmi_tty_port_ops = { |
230 | .activate = kgdb_nmi_tty_activate, |
231 | .shutdown = kgdb_nmi_tty_shutdown, |
232 | }; |
233 | |
234 | static int kgdb_nmi_tty_install(struct tty_driver *drv, struct tty_struct *tty) |
235 | { |
236 | struct kgdb_nmi_tty_priv *priv; |
237 | int ret; |
238 | |
239 | priv = kzalloc(size: sizeof(*priv), GFP_KERNEL); |
240 | if (!priv) |
241 | return -ENOMEM; |
242 | |
243 | INIT_KFIFO(priv->fifo); |
244 | timer_setup(&priv->timer, kgdb_nmi_tty_receiver, 0); |
245 | tty_port_init(port: &priv->port); |
246 | priv->port.ops = &kgdb_nmi_tty_port_ops; |
247 | tty->driver_data = priv; |
248 | |
249 | ret = tty_port_install(port: &priv->port, driver: drv, tty); |
250 | if (ret) { |
251 | pr_err("%s: can't install tty port: %d\n" , __func__, ret); |
252 | goto err; |
253 | } |
254 | return 0; |
255 | err: |
256 | tty_port_destroy(port: &priv->port); |
257 | kfree(objp: priv); |
258 | return ret; |
259 | } |
260 | |
261 | static void kgdb_nmi_tty_cleanup(struct tty_struct *tty) |
262 | { |
263 | struct kgdb_nmi_tty_priv *priv = tty->driver_data; |
264 | |
265 | tty->driver_data = NULL; |
266 | tty_port_destroy(port: &priv->port); |
267 | kfree(objp: priv); |
268 | } |
269 | |
270 | static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file) |
271 | { |
272 | struct kgdb_nmi_tty_priv *priv = tty->driver_data; |
273 | unsigned int mode = file->f_flags & O_ACCMODE; |
274 | int ret; |
275 | |
276 | ret = tty_port_open(port: &priv->port, tty, filp: file); |
277 | if (!ret && (mode == O_RDONLY || mode == O_RDWR)) |
278 | atomic_inc(v: &kgdb_nmi_num_readers); |
279 | |
280 | return ret; |
281 | } |
282 | |
283 | static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file) |
284 | { |
285 | struct kgdb_nmi_tty_priv *priv = tty->driver_data; |
286 | unsigned int mode = file->f_flags & O_ACCMODE; |
287 | |
288 | if (mode == O_RDONLY || mode == O_RDWR) |
289 | atomic_dec(v: &kgdb_nmi_num_readers); |
290 | |
291 | tty_port_close(port: &priv->port, tty, filp: file); |
292 | } |
293 | |
294 | static void kgdb_nmi_tty_hangup(struct tty_struct *tty) |
295 | { |
296 | struct kgdb_nmi_tty_priv *priv = tty->driver_data; |
297 | |
298 | tty_port_hangup(port: &priv->port); |
299 | } |
300 | |
301 | static unsigned int kgdb_nmi_tty_write_room(struct tty_struct *tty) |
302 | { |
303 | /* Actually, we can handle any amount as we use polled writes. */ |
304 | return 2048; |
305 | } |
306 | |
307 | static ssize_t kgdb_nmi_tty_write(struct tty_struct *tty, const u8 *buf, |
308 | size_t c) |
309 | { |
310 | int i; |
311 | |
312 | for (i = 0; i < c; i++) |
313 | dbg_io_ops->write_char(buf[i]); |
314 | return c; |
315 | } |
316 | |
317 | static const struct tty_operations kgdb_nmi_tty_ops = { |
318 | .open = kgdb_nmi_tty_open, |
319 | .close = kgdb_nmi_tty_close, |
320 | .install = kgdb_nmi_tty_install, |
321 | .cleanup = kgdb_nmi_tty_cleanup, |
322 | .hangup = kgdb_nmi_tty_hangup, |
323 | .write_room = kgdb_nmi_tty_write_room, |
324 | .write = kgdb_nmi_tty_write, |
325 | }; |
326 | |
327 | int kgdb_register_nmi_console(void) |
328 | { |
329 | int ret; |
330 | |
331 | if (!arch_kgdb_ops.enable_nmi) |
332 | return 0; |
333 | |
334 | kgdb_nmi_tty_driver = tty_alloc_driver(1, TTY_DRIVER_REAL_RAW); |
335 | if (IS_ERR(ptr: kgdb_nmi_tty_driver)) { |
336 | pr_err("%s: cannot allocate tty\n" , __func__); |
337 | return PTR_ERR(ptr: kgdb_nmi_tty_driver); |
338 | } |
339 | kgdb_nmi_tty_driver->driver_name = "ttyNMI" ; |
340 | kgdb_nmi_tty_driver->name = "ttyNMI" ; |
341 | kgdb_nmi_tty_driver->num = 1; |
342 | kgdb_nmi_tty_driver->type = TTY_DRIVER_TYPE_SERIAL; |
343 | kgdb_nmi_tty_driver->subtype = SERIAL_TYPE_NORMAL; |
344 | kgdb_nmi_tty_driver->init_termios = tty_std_termios; |
345 | tty_termios_encode_baud_rate(termios: &kgdb_nmi_tty_driver->init_termios, |
346 | KGDB_NMI_BAUD, KGDB_NMI_BAUD); |
347 | tty_set_operations(driver: kgdb_nmi_tty_driver, op: &kgdb_nmi_tty_ops); |
348 | |
349 | ret = tty_register_driver(driver: kgdb_nmi_tty_driver); |
350 | if (ret) { |
351 | pr_err("%s: can't register tty driver: %d\n" , __func__, ret); |
352 | goto err_drv_reg; |
353 | } |
354 | |
355 | register_console(&kgdb_nmi_console); |
356 | |
357 | return 0; |
358 | err_drv_reg: |
359 | tty_driver_kref_put(driver: kgdb_nmi_tty_driver); |
360 | return ret; |
361 | } |
362 | EXPORT_SYMBOL_GPL(kgdb_register_nmi_console); |
363 | |
364 | int kgdb_unregister_nmi_console(void) |
365 | { |
366 | int ret; |
367 | |
368 | if (!arch_kgdb_ops.enable_nmi) |
369 | return 0; |
370 | arch_kgdb_ops.enable_nmi(0); |
371 | |
372 | ret = unregister_console(&kgdb_nmi_console); |
373 | if (ret) |
374 | return ret; |
375 | |
376 | tty_unregister_driver(driver: kgdb_nmi_tty_driver); |
377 | tty_driver_kref_put(driver: kgdb_nmi_tty_driver); |
378 | |
379 | return 0; |
380 | } |
381 | EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console); |
382 | |