drivers/tty/serial/kgdb_nmi.c

   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 = -1;
 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(&kgdb_nmi_num_readers)) {
 139                 kgdb_tty_recv(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(&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(&priv->port, ch, TTY_NORMAL);
 205         tty_flip_buffer_push(&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(&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(&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(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(&priv->port);
 246         priv->port.ops = &kgdb_nmi_tty_port_ops;
 247         tty->driver_data = priv;
 248
 249         ret = tty_port_install(&priv->port, 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(&priv->port);
 257         kfree(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(&priv->port);
 267         kfree(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(&priv->port, tty, file);
 277         if (!ret && (mode == O_RDONLY || mode == O_RDWR))
 278                 atomic_inc(&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(&kgdb_nmi_num_readers);
 290
 291         tty_port_close(&priv->port, tty, 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(&priv->port);
 299 }
 300
 301 static 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 int kgdb_nmi_tty_write(struct tty_struct *tty, const unchar *buf, int c)
 308 {
 309         int i;
 310
 311         for (i = 0; i < c; i++)
 312                 dbg_io_ops->write_char(buf[i]);
 313         return c;
 314 }
 315
 316 static const struct tty_operations kgdb_nmi_tty_ops = {
 317         .open           = kgdb_nmi_tty_open,
 318         .close          = kgdb_nmi_tty_close,
 319         .install        = kgdb_nmi_tty_install,
 320         .cleanup        = kgdb_nmi_tty_cleanup,
 321         .hangup         = kgdb_nmi_tty_hangup,
 322         .write_room     = kgdb_nmi_tty_write_room,
 323         .write          = kgdb_nmi_tty_write,
 324 };
 325
 326 int kgdb_register_nmi_console(void)
 327 {
 328         int ret;
 329
 330         if (!arch_kgdb_ops.enable_nmi)
 331                 return 0;
 332
 333         kgdb_nmi_tty_driver = alloc_tty_driver(1);
 334         if (!kgdb_nmi_tty_driver) {
 335                 pr_err("%s: cannot allocate tty\n", __func__);
 336                 return -ENOMEM;
 337         }
 338         kgdb_nmi_tty_driver->driver_name        = "ttyNMI";
 339         kgdb_nmi_tty_driver->name               = "ttyNMI";
 340         kgdb_nmi_tty_driver->num                = 1;
 341         kgdb_nmi_tty_driver->type               = TTY_DRIVER_TYPE_SERIAL;
 342         kgdb_nmi_tty_driver->subtype            = SERIAL_TYPE_NORMAL;
 343         kgdb_nmi_tty_driver->flags              = TTY_DRIVER_REAL_RAW;
 344         kgdb_nmi_tty_driver->init_termios       = tty_std_termios;
 345         tty_termios_encode_baud_rate(&kgdb_nmi_tty_driver->init_termios,
 346                                      KGDB_NMI_BAUD, KGDB_NMI_BAUD);
 347         tty_set_operations(kgdb_nmi_tty_driver, &kgdb_nmi_tty_ops);
 348
 349         ret = tty_register_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         put_tty_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         ret = tty_unregister_driver(kgdb_nmi_tty_driver);
 377         if (ret)
 378                 return ret;
 379         put_tty_driver(kgdb_nmi_tty_driver);
 380
 381         return 0;
 382 }
 383 EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console);