kgdb patches for 6.10

Nine patches this cycle and they split into just three topics:
 
 1. Adopt coccinelle's recommendation to adopt str_plural().
 2. A set of seven patches to refactor kdb_read() to improve both code clarity
    and it's discipline with respect to fixed size buffers. This isn't just a
    refactor. Between them these also fix a cursor movement redraw problem and
    two buffer overflows (one latent and one real, albeit difficult to
    tickle).
 3. Fix an NMI-safety problem when enqueuing kdb's keyboard reset code.
 
 I wrote eight of the nine patches in this collection so many thanks to Doug
 Anderson for the reviews. The changes that affects drivers/tty/serial is
 acked by Greg KH.
 
 Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
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Merge tag 'kgdb-6.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux

Pull kgdb updates from Daniel Thompson:
 "Nine patches this cycle and they split into just three topics:

   - Adopt coccinelle's recommendation to adopt str_plural()

   - A set of seven patches to refactor kdb_read() to improve both code
     clarity and its discipline with respect to fixed size buffers.

     This isn't just a refactor. Between them these also fix a cursor
     movement redraw problem and two buffer overflows (one latent and
     one real, albeit difficult to tickle).

   - Fix an NMI-safety problem when enqueuing kdb's keyboard reset code

  I wrote eight of the nine patches in this collection so many thanks to
  Doug Anderson for the reviews. The changes that affects
  drivers/tty/serial is acked by Greg KH"

* tag 'kgdb-6.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/danielt/linux:
  serial: kgdboc: Fix NMI-safety problems from keyboard reset code
  kdb: Simplify management of tmpbuffer in kdb_read()
  kdb: Replace double memcpy() with memmove() in kdb_read()
  kdb: Use format-specifiers rather than memset() for padding in kdb_read()
  kdb: Merge identical case statements in kdb_read()
  kdb: Fix console handling when editing and tab-completing commands
  kdb: Use format-strings rather than '\0' injection in kdb_read()
  kdb: Fix buffer overflow during tab-complete
  kdb: Use str_plural() to fix Coccinelle warning

drivers/tty/serial/kgdboc.c

@@ -19,6 +19,7 @@
 #include <linux/console.h>
 #include <linux/vt_kern.h>
 #include <linux/input.h>
+#include <linux/irq_work.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/serial_core.h>
@@ -48,6 +49,25 @@ static struct kgdb_io		kgdboc_earlycon_io_ops;
 static int                      (*earlycon_orig_exit)(struct console *con);
 #endif /* IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */
 
+/*
+ * When we leave the debug trap handler we need to reset the keyboard status
+ * (since the original keyboard state gets partially clobbered by kdb use of
+ * the keyboard).
+ *
+ * The path to deliver the reset is somewhat circuitous.
+ *
+ * To deliver the reset we register an input handler, reset the keyboard and
+ * then deregister the input handler. However, to get this done right, we do
+ * have to carefully manage the calling context because we can only register
+ * input handlers from task context.
+ *
+ * In particular we need to trigger the action from the debug trap handler with
+ * all its NMI and/or NMI-like oddities. To solve this the kgdboc trap exit code
+ * (the "post_exception" callback) uses irq_work_queue(), which is NMI-safe, to
+ * schedule a callback from a hardirq context. From there we have to defer the
+ * work again, this time using schedule_work(), to get a callback using the
+ * system workqueue, which runs in task context.
+ */
 #ifdef CONFIG_KDB_KEYBOARD
 static int kgdboc_reset_connect(struct input_handler *handler,
 				struct input_dev *dev,
@@ -99,10 +119,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
 
 static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
 
+static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
+{
+	schedule_work(&kgdboc_restore_input_work);
+}
+
+static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
+
 static void kgdboc_restore_input(void)
 {
 	if (likely(system_state == SYSTEM_RUNNING))
-		schedule_work(&kgdboc_restore_input_work);
+		irq_work_queue(&kgdboc_restore_input_irq_work);
 }
 
 static int kgdboc_register_kbd(char **cptr)
@@ -133,6 +160,7 @@ static void kgdboc_unregister_kbd(void)
 			i--;
 		}
 	}
+	irq_work_sync(&kgdboc_restore_input_irq_work);
 	flush_work(&kgdboc_restore_input_work);
 }
 #else /* ! CONFIG_KDB_KEYBOARD */

kernel/debug/kdb/kdb_io.c

@@ -184,6 +184,33 @@ char kdb_getchar(void)
 	unreachable();
 }
 
+/**
+ * kdb_position_cursor() - Place cursor in the correct horizontal position
+ * @prompt: Nil-terminated string containing the prompt string
+ * @buffer: Nil-terminated string containing the entire command line
+ * @cp: Cursor position, pointer the character in buffer where the cursor
+ *      should be positioned.
+ *
+ * The cursor is positioned by sending a carriage-return and then printing
+ * the content of the line until we reach the correct cursor position.
+ *
+ * There is some additional fine detail here.
+ *
+ * Firstly, even though kdb_printf() will correctly format zero-width fields
+ * we want the second call to kdb_printf() to be conditional. That keeps things
+ * a little cleaner when LOGGING=1.
+ *
+ * Secondly, we can't combine everything into one call to kdb_printf() since
+ * that renders into a fixed length buffer and the combined print could result
+ * in unwanted truncation.
+ */
+static void kdb_position_cursor(char *prompt, char *buffer, char *cp)
+{
+	kdb_printf("\r%s", kdb_prompt_str);
+	if (cp > buffer)
+		kdb_printf("%.*s", (int)(cp - buffer), buffer);
+}
+
 /*
  * kdb_read
  *
@@ -220,8 +247,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
 	int count;
 	int i;
 	int diag, dtab_count;
-	int key, buf_size, ret;
-
+	int key, ret;
 
 	diag = kdbgetintenv("DTABCOUNT", &dtab_count);
 	if (diag)
@@ -243,18 +269,11 @@ poll_again:
 	switch (key) {
 	case 8: /* backspace */
 		if (cp > buffer) {
-			if (cp < lastchar) {
-				memcpy(tmpbuffer, cp, lastchar - cp);
-				memcpy(cp-1, tmpbuffer, lastchar - cp);
-			}
-			*(--lastchar) = '\0';
-			--cp;
-			kdb_printf("\b%s \r", cp);
-			tmp = *cp;
-			*cp = '\0';
-			kdb_printf(kdb_prompt_str);
-			kdb_printf("%s", buffer);
-			*cp = tmp;
+			memmove(cp-1, cp, lastchar - cp + 1);
+			lastchar--;
+			cp--;
+			kdb_printf("\b%s ", cp);
+			kdb_position_cursor(kdb_prompt_str, buffer, cp);
 		}
 		break;
 	case 10: /* linefeed */
@@ -269,22 +288,16 @@ poll_again:
 		return buffer;
 	case 4: /* Del */
 		if (cp < lastchar) {
-			memcpy(tmpbuffer, cp+1, lastchar - cp - 1);
-			memcpy(cp, tmpbuffer, lastchar - cp - 1);
-			*(--lastchar) = '\0';
-			kdb_printf("%s \r", cp);
-			tmp = *cp;
-			*cp = '\0';
-			kdb_printf(kdb_prompt_str);
-			kdb_printf("%s", buffer);
-			*cp = tmp;
+			memmove(cp, cp+1, lastchar - cp);
+			lastchar--;
+			kdb_printf("%s ", cp);
+			kdb_position_cursor(kdb_prompt_str, buffer, cp);
 		}
 		break;
 	case 1: /* Home */
 		if (cp > buffer) {
-			kdb_printf("\r");
-			kdb_printf(kdb_prompt_str);
 			cp = buffer;
+			kdb_position_cursor(kdb_prompt_str, buffer, cp);
 		}
 		break;
 	case 5: /* End */
@@ -300,11 +313,10 @@ poll_again:
 		}
 		break;
 	case 14: /* Down */
-		memset(tmpbuffer, ' ',
-		       strlen(kdb_prompt_str) + (lastchar-buffer));
-		*(tmpbuffer+strlen(kdb_prompt_str) +
-		  (lastchar-buffer)) = '\0';
-		kdb_printf("\r%s\r", tmpbuffer);
+	case 16: /* Up */
+		kdb_printf("\r%*c\r",
+			   (int)(strlen(kdb_prompt_str) + (lastchar - buffer)),
+			   ' ');
 		*lastchar = (char)key;
 		*(lastchar+1) = '\0';
 		return lastchar;
@@ -314,33 +326,19 @@ poll_again:
 			++cp;
 		}
 		break;
-	case 16: /* Up */
-		memset(tmpbuffer, ' ',
-		       strlen(kdb_prompt_str) + (lastchar-buffer));
-		*(tmpbuffer+strlen(kdb_prompt_str) +
-		  (lastchar-buffer)) = '\0';
-		kdb_printf("\r%s\r", tmpbuffer);
-		*lastchar = (char)key;
-		*(lastchar+1) = '\0';
-		return lastchar;
 	case 9: /* Tab */
 		if (tab < 2)
 			++tab;
-		p_tmp = buffer;
-		while (*p_tmp == ' ')
-			p_tmp++;
-		if (p_tmp > cp)
-			break;
-		memcpy(tmpbuffer, p_tmp, cp-p_tmp);
-		*(tmpbuffer + (cp-p_tmp)) = '\0';
-		p_tmp = strrchr(tmpbuffer, ' ');
-		if (p_tmp)
-			++p_tmp;
-		else
-			p_tmp = tmpbuffer;
-		len = strlen(p_tmp);
-		buf_size = sizeof(tmpbuffer) - (p_tmp - tmpbuffer);
-		count = kallsyms_symbol_complete(p_tmp, buf_size);
+
+		tmp = *cp;
+		*cp = '\0';
+		p_tmp = strrchr(buffer, ' ');
+		p_tmp = (p_tmp ? p_tmp + 1 : buffer);
+		strscpy(tmpbuffer, p_tmp, sizeof(tmpbuffer));
+		*cp = tmp;
+
+		len = strlen(tmpbuffer);
+		count = kallsyms_symbol_complete(tmpbuffer, sizeof(tmpbuffer));
 		if (tab == 2 && count > 0) {
 			kdb_printf("\n%d symbols are found.", count);
 			if (count > dtab_count) {
@@ -352,46 +350,51 @@ poll_again:
 			}
 			kdb_printf("\n");
 			for (i = 0; i < count; i++) {
-				ret = kallsyms_symbol_next(p_tmp, i, buf_size);
+				ret = kallsyms_symbol_next(tmpbuffer, i, sizeof(tmpbuffer));
 				if (WARN_ON(!ret))
 					break;
 				if (ret != -E2BIG)
-					kdb_printf("%s ", p_tmp);
+					kdb_printf("%s ", tmpbuffer);
 				else
-					kdb_printf("%s... ", p_tmp);
-				*(p_tmp + len) = '\0';
+					kdb_printf("%s... ", tmpbuffer);
+				tmpbuffer[len] = '\0';
 			}
 			if (i >= dtab_count)
 				kdb_printf("...");
 			kdb_printf("\n");
 			kdb_printf(kdb_prompt_str);
 			kdb_printf("%s", buffer);
+			if (cp != lastchar)
+				kdb_position_cursor(kdb_prompt_str, buffer, cp);
 		} else if (tab != 2 && count > 0) {
-			len_tmp = strlen(p_tmp);
-			strncpy(p_tmp+len_tmp, cp, lastchar-cp+1);
-			len_tmp = strlen(p_tmp);
-			strncpy(cp, p_tmp+len, len_tmp-len + 1);
-			len = len_tmp - len;
-			kdb_printf("%s", cp);
-			cp += len;
-			lastchar += len;
+			/* How many new characters do we want from tmpbuffer? */
+			len_tmp = strlen(tmpbuffer) - len;
+			if (lastchar + len_tmp >= bufend)
+				len_tmp = bufend - lastchar;
+
+			if (len_tmp) {
+				/* + 1 ensures the '\0' is memmove'd */
+				memmove(cp+len_tmp, cp, (lastchar-cp) + 1);
+				memcpy(cp, tmpbuffer+len, len_tmp);
+				kdb_printf("%s", cp);
+				cp += len_tmp;
+				lastchar += len_tmp;
+				if (cp != lastchar)
+					kdb_position_cursor(kdb_prompt_str,
+							    buffer, cp);
+			}
 		}
 		kdb_nextline = 1; /* reset output line number */
 		break;
 	default:
 		if (key >= 32 && lastchar < bufend) {
 			if (cp < lastchar) {
-				memcpy(tmpbuffer, cp, lastchar - cp);
-				memcpy(cp+1, tmpbuffer, lastchar - cp);
-				*++lastchar = '\0';
+				memmove(cp+1, cp, lastchar - cp + 1);
+				lastchar++;
 				*cp = key;
-				kdb_printf("%s\r", cp);
+				kdb_printf("%s", cp);
 				++cp;
-				tmp = *cp;
-				*cp = '\0';
-				kdb_printf(kdb_prompt_str);
-				kdb_printf("%s", buffer);
-				*cp = tmp;
+				kdb_position_cursor(kdb_prompt_str, buffer, cp);
 			} else {
 				*++lastchar = '\0';
 				*cp++ = key;

kernel/debug/kdb/kdb_main.c

@@ -2517,7 +2517,7 @@ static int kdb_summary(int argc, const char **argv)
 	if (val.uptime > (24*60*60)) {
 		int days = val.uptime / (24*60*60);
 		val.uptime %= (24*60*60);
-		kdb_printf("%d day%s ", days, days == 1 ? "" : "s");
+		kdb_printf("%d day%s ", days, str_plural(days));
 	}
 	kdb_printf("%02ld:%02ld\n", val.uptime/(60*60), (val.uptime/60)%60);