Merge tag 'for_linus-3.19-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb

Pull kgdb/kdb fixes from Jason Wessel:
 "These have been around since 3.17 and in kgdb-next for the last 9
  weeks and some will go back to -stable.

  Summary of changes:

  Cleanups
   - kdb: Remove unused command flags, repeat flags and KDB_REPEAT_NONE

  Fixes
   - kgdb/kdb: Allow access on a single core, if a CPU round up is
     deemed impossible, which will allow inspection of the now "trashed"
     kernel
   - kdb: Add enable mask for the command groups
   - kdb: access controls to restrict sensitive commands"

* tag 'for_linus-3.19-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb:
  kernel/debug/debug_core.c: Logging clean-up
  kgdb: timeout if secondary CPUs ignore the roundup
  kdb: Allow access to sensitive commands to be restricted by default
  kdb: Add enable mask for groups of commands
  kdb: Categorize kdb commands (similar to SysRq categorization)
  kdb: Remove KDB_REPEAT_NONE flag
  kdb: Use KDB_REPEAT_* values as flags
  kdb: Rename kdb_register_repeat() to kdb_register_flags()
  kdb: Rename kdb_repeat_t to kdb_cmdflags_t, cmd_repeat to cmd_flags
  kdb: Remove currently unused kdbtab_t->cmd_flags

8 files changed, 306 insertions, 148 deletions

diff --git a/include/linux/kdb.h b/include/linux/kdb.h
index 290db1269c4c..75ae2e2631fc 100644
--- a/include/linux/kdb.h
+++ b/include/linux/kdb.h
@@ -13,11 +13,54 @@
  * Copyright (C) 2009 Jason Wessel <jason.wessel@windriver.com>
  */
 
+/* Shifted versions of the command enable bits are be used if the command
+ * has no arguments (see kdb_check_flags). This allows commands, such as
+ * go, to have different permissions depending upon whether it is called
+ * with an argument.
+ */
+#define KDB_ENABLE_NO_ARGS_SHIFT 10
+
 typedef enum {
-	KDB_REPEAT_NONE = 0,	/* Do not repeat this command */
-	KDB_REPEAT_NO_ARGS,	/* Repeat the command without arguments */
-	KDB_REPEAT_WITH_ARGS,	/* Repeat the command including its arguments */
-} kdb_repeat_t;
+	KDB_ENABLE_ALL = (1 << 0), /* Enable everything */
+	KDB_ENABLE_MEM_READ = (1 << 1),
+	KDB_ENABLE_MEM_WRITE = (1 << 2),
+	KDB_ENABLE_REG_READ = (1 << 3),
+	KDB_ENABLE_REG_WRITE = (1 << 4),
+	KDB_ENABLE_INSPECT = (1 << 5),
+	KDB_ENABLE_FLOW_CTRL = (1 << 6),
+	KDB_ENABLE_SIGNAL = (1 << 7),
+	KDB_ENABLE_REBOOT = (1 << 8),
+	/* User exposed values stop here, all remaining flags are
+	 * exclusively used to describe a commands behaviour.
+	 */
+
+	KDB_ENABLE_ALWAYS_SAFE = (1 << 9),
+	KDB_ENABLE_MASK = (1 << KDB_ENABLE_NO_ARGS_SHIFT) - 1,
+
+	KDB_ENABLE_ALL_NO_ARGS = KDB_ENABLE_ALL << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_MEM_READ_NO_ARGS = KDB_ENABLE_MEM_READ
+				      << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_MEM_WRITE_NO_ARGS = KDB_ENABLE_MEM_WRITE
+				       << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_REG_READ_NO_ARGS = KDB_ENABLE_REG_READ
+				      << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_REG_WRITE_NO_ARGS = KDB_ENABLE_REG_WRITE
+				       << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_INSPECT_NO_ARGS = KDB_ENABLE_INSPECT
+				     << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_FLOW_CTRL_NO_ARGS = KDB_ENABLE_FLOW_CTRL
+				       << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_SIGNAL_NO_ARGS = KDB_ENABLE_SIGNAL
+				    << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_REBOOT_NO_ARGS = KDB_ENABLE_REBOOT
+				    << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_ALWAYS_SAFE_NO_ARGS = KDB_ENABLE_ALWAYS_SAFE
+					 << KDB_ENABLE_NO_ARGS_SHIFT,
+	KDB_ENABLE_MASK_NO_ARGS = KDB_ENABLE_MASK << KDB_ENABLE_NO_ARGS_SHIFT,
+
+	KDB_REPEAT_NO_ARGS = 0x40000000, /* Repeat the command w/o arguments */
+	KDB_REPEAT_WITH_ARGS = 0x80000000, /* Repeat the command with args */
+} kdb_cmdflags_t;
 
 typedef int (*kdb_func_t)(int, const char **);
 
@@ -62,6 +105,7 @@ extern atomic_t kdb_event;
 #define KDB_BADLENGTH	(-19)
 #define KDB_NOBP	(-20)
 #define KDB_BADADDR	(-21)
+#define KDB_NOPERM	(-22)
 
 /*
  * kdb_diemsg
@@ -146,17 +190,17 @@ static inline const char *kdb_walk_kallsyms(loff_t *pos)
 
 /* Dynamic kdb shell command registration */
 extern int kdb_register(char *, kdb_func_t, char *, char *, short);
-extern int kdb_register_repeat(char *, kdb_func_t, char *, char *,
-			       short, kdb_repeat_t);
+extern int kdb_register_flags(char *, kdb_func_t, char *, char *,
+			      short, kdb_cmdflags_t);
 extern int kdb_unregister(char *);
 #else /* ! CONFIG_KGDB_KDB */
 static inline __printf(1, 2) int kdb_printf(const char *fmt, ...) { return 0; }
 static inline void kdb_init(int level) {}
 static inline int kdb_register(char *cmd, kdb_func_t func, char *usage,
 			       char *help, short minlen) { return 0; }
-static inline int kdb_register_repeat(char *cmd, kdb_func_t func, char *usage,
-				      char *help, short minlen,
-				      kdb_repeat_t repeat) { return 0; }
+static inline int kdb_register_flags(char *cmd, kdb_func_t func, char *usage,
+				     char *help, short minlen,
+				     kdb_cmdflags_t flags) { return 0; }
 static inline int kdb_unregister(char *cmd) { return 0; }
 #endif	/* CONFIG_KGDB_KDB */
 enum {
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 1adf62b39b96..07ce18ca71e0 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -27,6 +27,9 @@
  * version 2. This program is licensed "as is" without any warranty of any
  * kind, whether express or implied.
  */
+
+#define pr_fmt(fmt) "KGDB: " fmt
+
 #include <linux/pid_namespace.h>
 #include <linux/clocksource.h>
 #include <linux/serial_core.h>
@@ -196,8 +199,8 @@ int __weak kgdb_validate_break_address(unsigned long addr)
 		return err;
 	err = kgdb_arch_remove_breakpoint(&tmp);
 	if (err)
-		printk(KERN_ERR "KGDB: Critical breakpoint error, kernel "
-		   "memory destroyed at: %lx", addr);
+		pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
+		       addr);
 	return err;
 }
 
@@ -256,8 +259,8 @@ int dbg_activate_sw_breakpoints(void)
 		error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 		if (error) {
 			ret = error;
-			printk(KERN_INFO "KGDB: BP install failed: %lx",
-			       kgdb_break[i].bpt_addr);
+			pr_info("BP install failed: %lx\n",
+				kgdb_break[i].bpt_addr);
 			continue;
 		}
 
@@ -319,8 +322,8 @@ int dbg_deactivate_sw_breakpoints(void)
 			continue;
 		error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 		if (error) {
-			printk(KERN_INFO "KGDB: BP remove failed: %lx\n",
-			       kgdb_break[i].bpt_addr);
+			pr_info("BP remove failed: %lx\n",
+				kgdb_break[i].bpt_addr);
 			ret = error;
 		}
 
@@ -367,7 +370,7 @@ int dbg_remove_all_break(void)
 			goto setundefined;
 		error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 		if (error)
-			printk(KERN_ERR "KGDB: breakpoint remove failed: %lx\n",
+			pr_err("breakpoint remove failed: %lx\n",
 			       kgdb_break[i].bpt_addr);
 setundefined:
 		kgdb_break[i].state = BP_UNDEFINED;
@@ -400,9 +403,9 @@ static int kgdb_io_ready(int print_wait)
 	if (print_wait) {
 #ifdef CONFIG_KGDB_KDB
 		if (!dbg_kdb_mode)
-			printk(KERN_CRIT "KGDB: waiting... or $3#33 for KDB\n");
+			pr_crit("waiting... or $3#33 for KDB\n");
 #else
-		printk(KERN_CRIT "KGDB: Waiting for remote debugger\n");
+		pr_crit("Waiting for remote debugger\n");
 #endif
 	}
 	return 1;
@@ -430,8 +433,7 @@ static int kgdb_reenter_check(struct kgdb_state *ks)
 		exception_level = 0;
 		kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 		dbg_activate_sw_breakpoints();
-		printk(KERN_CRIT "KGDB: re-enter error: breakpoint removed %lx\n",
-			addr);
+		pr_crit("re-enter error: breakpoint removed %lx\n", addr);
 		WARN_ON_ONCE(1);
 
 		return 1;
@@ -444,7 +446,7 @@ static int kgdb_reenter_check(struct kgdb_state *ks)
 		panic("Recursive entry to debugger");
 	}
 
-	printk(KERN_CRIT "KGDB: re-enter exception: ALL breakpoints killed\n");
+	pr_crit("re-enter exception: ALL breakpoints killed\n");
 #ifdef CONFIG_KGDB_KDB
 	/* Allow kdb to debug itself one level */
 	return 0;
@@ -471,6 +473,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 	int cpu;
 	int trace_on = 0;
 	int online_cpus = num_online_cpus();
+	u64 time_left;
 
 	kgdb_info[ks->cpu].enter_kgdb++;
 	kgdb_info[ks->cpu].exception_state |= exception_state;
@@ -595,9 +598,13 @@ return_normal:
 	/*
 	 * Wait for the other CPUs to be notified and be waiting for us:
 	 */
-	while (kgdb_do_roundup && (atomic_read(&masters_in_kgdb) +
-				atomic_read(&slaves_in_kgdb)) != online_cpus)
+	time_left = loops_per_jiffy * HZ;
+	while (kgdb_do_roundup && --time_left &&
+	       (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
+		   online_cpus)
 		cpu_relax();
+	if (!time_left)
+		pr_crit("KGDB: Timed out waiting for secondary CPUs.\n");
 
 	/*
 	 * At this point the primary processor is completely
@@ -795,15 +802,15 @@ static struct console kgdbcons = {
 static void sysrq_handle_dbg(int key)
 {
 	if (!dbg_io_ops) {
-		printk(KERN_CRIT "ERROR: No KGDB I/O module available\n");
+		pr_crit("ERROR: No KGDB I/O module available\n");
 		return;
 	}
 	if (!kgdb_connected) {
 #ifdef CONFIG_KGDB_KDB
 		if (!dbg_kdb_mode)
-			printk(KERN_CRIT "KGDB or $3#33 for KDB\n");
+			pr_crit("KGDB or $3#33 for KDB\n");
 #else
-		printk(KERN_CRIT "Entering KGDB\n");
+		pr_crit("Entering KGDB\n");
 #endif
 	}
 
@@ -945,7 +952,7 @@ static void kgdb_initial_breakpoint(void)
 {
 	kgdb_break_asap = 0;
 
-	printk(KERN_CRIT "kgdb: Waiting for connection from remote gdb...\n");
+	pr_crit("Waiting for connection from remote gdb...\n");
 	kgdb_breakpoint();
 }
 
@@ -964,8 +971,7 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 	if (dbg_io_ops) {
 		spin_unlock(&kgdb_registration_lock);
 
-		printk(KERN_ERR "kgdb: Another I/O driver is already "
-				"registered with KGDB.\n");
+		pr_err("Another I/O driver is already registered with KGDB\n");
 		return -EBUSY;
 	}
 
@@ -981,8 +987,7 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 
 	spin_unlock(&kgdb_registration_lock);
 
-	printk(KERN_INFO "kgdb: Registered I/O driver %s.\n",
-	       new_dbg_io_ops->name);
+	pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
 
 	/* Arm KGDB now. */
 	kgdb_register_callbacks();
@@ -1017,8 +1022,7 @@ void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
 
 	spin_unlock(&kgdb_registration_lock);
 
-	printk(KERN_INFO
-		"kgdb: Unregistered I/O driver %s, debugger disabled.\n",
+	pr_info("Unregistered I/O driver %s, debugger disabled\n",
 		old_dbg_io_ops->name);
 }
 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
diff --git a/kernel/debug/kdb/kdb_bp.c b/kernel/debug/kdb/kdb_bp.c
index b20d544f20c2..e1dbf4a2c69e 100644
--- a/kernel/debug/kdb/kdb_bp.c
+++ b/kernel/debug/kdb/kdb_bp.c
@@ -531,22 +531,29 @@ void __init kdb_initbptab(void)
 	for (i = 0, bp = kdb_breakpoints; i < KDB_MAXBPT; i++, bp++)
 		bp->bp_free = 1;
 
-	kdb_register_repeat("bp", kdb_bp, "[<vaddr>]",
-		"Set/Display breakpoints", 0, KDB_REPEAT_NO_ARGS);
-	kdb_register_repeat("bl", kdb_bp, "[<vaddr>]",
-		"Display breakpoints", 0, KDB_REPEAT_NO_ARGS);
+	kdb_register_flags("bp", kdb_bp, "[<vaddr>]",
+		"Set/Display breakpoints", 0,
+		KDB_ENABLE_FLOW_CTRL | KDB_REPEAT_NO_ARGS);
+	kdb_register_flags("bl", kdb_bp, "[<vaddr>]",
+		"Display breakpoints", 0,
+		KDB_ENABLE_FLOW_CTRL | KDB_REPEAT_NO_ARGS);
 	if (arch_kgdb_ops.flags & KGDB_HW_BREAKPOINT)
-		kdb_register_repeat("bph", kdb_bp, "[<vaddr>]",
-		"[datar [length]|dataw [length]]   Set hw brk", 0, KDB_REPEAT_NO_ARGS);
-	kdb_register_repeat("bc", kdb_bc, "<bpnum>",
-		"Clear Breakpoint", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("be", kdb_bc, "<bpnum>",
-		"Enable Breakpoint", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("bd", kdb_bc, "<bpnum>",
-		"Disable Breakpoint", 0, KDB_REPEAT_NONE);
-
-	kdb_register_repeat("ss", kdb_ss, "",
-		"Single Step", 1, KDB_REPEAT_NO_ARGS);
+		kdb_register_flags("bph", kdb_bp, "[<vaddr>]",
+		"[datar [length]|dataw [length]]   Set hw brk", 0,
+		KDB_ENABLE_FLOW_CTRL | KDB_REPEAT_NO_ARGS);
+	kdb_register_flags("bc", kdb_bc, "<bpnum>",
+		"Clear Breakpoint", 0,
+		KDB_ENABLE_FLOW_CTRL);
+	kdb_register_flags("be", kdb_bc, "<bpnum>",
+		"Enable Breakpoint", 0,
+		KDB_ENABLE_FLOW_CTRL);
+	kdb_register_flags("bd", kdb_bc, "<bpnum>",
+		"Disable Breakpoint", 0,
+		KDB_ENABLE_FLOW_CTRL);
+
+	kdb_register_flags("ss", kdb_ss, "",
+		"Single Step", 1,
+		KDB_ENABLE_FLOW_CTRL | KDB_REPEAT_NO_ARGS);
 	/*
 	 * Architecture dependent initialization.
 	 */
diff --git a/kernel/debug/kdb/kdb_debugger.c b/kernel/debug/kdb/kdb_debugger.c
index 8859ca34dcfe..15e1a7af5dd0 100644
--- a/kernel/debug/kdb/kdb_debugger.c
+++ b/kernel/debug/kdb/kdb_debugger.c
@@ -129,6 +129,10 @@ int kdb_stub(struct kgdb_state *ks)
 		ks->pass_exception = 1;
 		KDB_FLAG_SET(CATASTROPHIC);
 	}
+	/* set CATASTROPHIC if the system contains unresponsive processors */
+	for_each_online_cpu(i)
+		if (!kgdb_info[i].enter_kgdb)
+			KDB_FLAG_SET(CATASTROPHIC);
 	if (KDB_STATE(SSBPT) && reason == KDB_REASON_SSTEP) {
 		KDB_STATE_CLEAR(SSBPT);
 		KDB_STATE_CLEAR(DOING_SS);
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 379650b984f8..f191bddf64b8 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -12,6 +12,7 @@
  */
 
 #include <linux/ctype.h>
+#include <linux/types.h>
 #include <linux/string.h>
 #include <linux/kernel.h>
 #include <linux/kmsg_dump.h>
@@ -23,6 +24,7 @@
 #include <linux/vmalloc.h>
 #include <linux/atomic.h>
 #include <linux/module.h>
+#include <linux/moduleparam.h>
 #include <linux/mm.h>
 #include <linux/init.h>
 #include <linux/kallsyms.h>
@@ -42,6 +44,12 @@
 #include <linux/slab.h>
 #include "kdb_private.h"
 
+#undef	MODULE_PARAM_PREFIX
+#define	MODULE_PARAM_PREFIX "kdb."
+
+static int kdb_cmd_enabled = CONFIG_KDB_DEFAULT_ENABLE;
+module_param_named(cmd_enable, kdb_cmd_enabled, int, 0600);
+
 #define GREP_LEN 256
 char kdb_grep_string[GREP_LEN];
 int kdb_grepping_flag;
@@ -121,6 +129,7 @@ static kdbmsg_t kdbmsgs[] = {
 	KDBMSG(BADLENGTH, "Invalid length field"),
 	KDBMSG(NOBP, "No Breakpoint exists"),
 	KDBMSG(BADADDR, "Invalid address"),
+	KDBMSG(NOPERM, "Permission denied"),
 };
 #undef KDBMSG
 
@@ -188,6 +197,26 @@ struct task_struct *kdb_curr_task(int cpu)
 }
 
 /*
+ * Check whether the flags of the current command and the permissions
+ * of the kdb console has allow a command to be run.
+ */
+static inline bool kdb_check_flags(kdb_cmdflags_t flags, int permissions,
+				   bool no_args)
+{
+	/* permissions comes from userspace so needs massaging slightly */
+	permissions &= KDB_ENABLE_MASK;
+	permissions |= KDB_ENABLE_ALWAYS_SAFE;
+
+	/* some commands change group when launched with no arguments */
+	if (no_args)
+		permissions |= permissions << KDB_ENABLE_NO_ARGS_SHIFT;
+
+	flags |= KDB_ENABLE_ALL;
+
+	return permissions & flags;
+}
+
+/*
  * kdbgetenv - This function will return the character string value of
  *	an environment variable.
  * Parameters:
@@ -476,6 +505,15 @@ int kdbgetaddrarg(int argc, const char **argv, int *nextarg,
 	kdb_symtab_t symtab;
 
 	/*
+	 * If the enable flags prohibit both arbitrary memory access
+	 * and flow control then there are no reasonable grounds to
+	 * provide symbol lookup.
+	 */
+	if (!kdb_check_flags(KDB_ENABLE_MEM_READ | KDB_ENABLE_FLOW_CTRL,
+			     kdb_cmd_enabled, false))
+		return KDB_NOPERM;
+
+	/*
 	 * Process arguments which follow the following syntax:
 	 *
 	 *  symbol | numeric-address [+/- numeric-offset]
@@ -641,8 +679,13 @@ static int kdb_defcmd2(const char *cmdstr, const char *argv0)
 		if (!s->count)
 			s->usable = 0;
 		if (s->usable)
-			kdb_register(s->name, kdb_exec_defcmd,
-				     s->usage, s->help, 0);
+			/* macros are always safe because when executed each
+			 * internal command re-enters kdb_parse() and is
+			 * safety checked individually.
+			 */
+			kdb_register_flags(s->name, kdb_exec_defcmd, s->usage,
+					   s->help, 0,
+					   KDB_ENABLE_ALWAYS_SAFE);
 		return 0;
 	}
 	if (!s->usable)
@@ -1003,25 +1046,22 @@ int kdb_parse(const char *cmdstr)
 
 	if (i < kdb_max_commands) {
 		int result;
+
+		if (!kdb_check_flags(tp->cmd_flags, kdb_cmd_enabled, argc <= 1))
+			return KDB_NOPERM;
+
 		KDB_STATE_SET(CMD);
 		result = (*tp->cmd_func)(argc-1, (const char **)argv);
 		if (result && ignore_errors && result > KDB_CMD_GO)
 			result = 0;
 		KDB_STATE_CLEAR(CMD);
-		switch (tp->cmd_repeat) {
-		case KDB_REPEAT_NONE:
-			argc = 0;
-			if (argv[0])
-				*(argv[0]) = '\0';
-			break;
-		case KDB_REPEAT_NO_ARGS:
-			argc = 1;
-			if (argv[1])
-				*(argv[1]) = '\0';
-			break;
-		case KDB_REPEAT_WITH_ARGS:
-			break;
-		}
+
+		if (tp->cmd_flags & KDB_REPEAT_WITH_ARGS)
+			return result;
+
+		argc = tp->cmd_flags & KDB_REPEAT_NO_ARGS ? 1 : 0;
+		if (argv[argc])
+			*(argv[argc]) = '\0';
 		return result;
 	}
 
@@ -1921,10 +1961,14 @@ static int kdb_rm(int argc, const char **argv)
  */
 static int kdb_sr(int argc, const char **argv)
 {
+	bool check_mask =
+	    !kdb_check_flags(KDB_ENABLE_ALL, kdb_cmd_enabled, false);
+
 	if (argc != 1)
 		return KDB_ARGCOUNT;
+
 	kdb_trap_printk++;
-	__handle_sysrq(*argv[1], false);
+	__handle_sysrq(*argv[1], check_mask);
 	kdb_trap_printk--;
 
 	return 0;
@@ -2157,6 +2201,8 @@ static void kdb_cpu_status(void)
 	for (start_cpu = -1, i = 0; i < NR_CPUS; i++) {
 		if (!cpu_online(i)) {
 			state = 'F';	/* cpu is offline */
+		} else if (!kgdb_info[i].enter_kgdb) {
+			state = 'D';	/* cpu is online but unresponsive */
 		} else {
 			state = ' ';	/* cpu is responding to kdb */
 			if (kdb_task_state_char(KDB_TSK(i)) == 'I')
@@ -2210,7 +2256,7 @@ static int kdb_cpu(int argc, const char **argv)
 	/*
 	 * Validate cpunum
 	 */
-	if ((cpunum > NR_CPUS) || !cpu_online(cpunum))
+	if ((cpunum > NR_CPUS) || !kgdb_info[cpunum].enter_kgdb)
 		return KDB_BADCPUNUM;
 
 	dbg_switch_cpu = cpunum;
@@ -2375,6 +2421,8 @@ static int kdb_help(int argc, const char **argv)
 			return 0;
 		if (!kt->cmd_name)
 			continue;
+		if (!kdb_check_flags(kt->cmd_flags, kdb_cmd_enabled, true))
+			continue;
 		if (strlen(kt->cmd_usage) > 20)
 			space = "\n                                    ";
 		kdb_printf("%-15.15s %-20s%s%s\n", kt->cmd_name,
@@ -2629,7 +2677,7 @@ static int kdb_grep_help(int argc, const char **argv)
 }
 
 /*
- * kdb_register_repeat - This function is used to register a kernel
+ * kdb_register_flags - This function is used to register a kernel
  * 	debugger command.
  * Inputs:
  *	cmd	Command name
@@ -2641,12 +2689,12 @@ static int kdb_grep_help(int argc, const char **argv)
  *	zero for success, one if a duplicate command.
  */
 #define kdb_command_extend 50	/* arbitrary */
-int kdb_register_repeat(char *cmd,
-			kdb_func_t func,
-			char *usage,
-			char *help,
-			short minlen,
-			kdb_repeat_t repeat)
+int kdb_register_flags(char *cmd,
+		       kdb_func_t func,
+		       char *usage,
+		       char *help,
+		       short minlen,
+		       kdb_cmdflags_t flags)
 {
 	int i;
 	kdbtab_t *kp;
@@ -2694,19 +2742,18 @@ int kdb_register_repeat(char *cmd,
 	kp->cmd_func   = func;
 	kp->cmd_usage  = usage;
 	kp->cmd_help   = help;
-	kp->cmd_flags  = 0;
 	kp->cmd_minlen = minlen;
-	kp->cmd_repeat = repeat;
+	kp->cmd_flags  = flags;
 
 	return 0;
 }
-EXPORT_SYMBOL_GPL(kdb_register_repeat);
+EXPORT_SYMBOL_GPL(kdb_register_flags);
 
 
 /*
  * kdb_register - Compatibility register function for commands that do
  *	not need to specify a repeat state.  Equivalent to
- *	kdb_register_repeat with KDB_REPEAT_NONE.
+ *	kdb_register_flags with flags set to 0.
  * Inputs:
  *	cmd	Command name
  *	func	Function to execute the command
@@ -2721,8 +2768,7 @@ int kdb_register(char *cmd,
 	     char *help,
 	     short minlen)
 {
-	return kdb_register_repeat(cmd, func, usage, help, minlen,
-				   KDB_REPEAT_NONE);
+	return kdb_register_flags(cmd, func, usage, help, minlen, 0);
 }
 EXPORT_SYMBOL_GPL(kdb_register);
 
@@ -2764,80 +2810,109 @@ static void __init kdb_inittab(void)
 	for_each_kdbcmd(kp, i)
 		kp->cmd_name = NULL;
 
-	kdb_register_repeat("md", kdb_md, "<vaddr>",
+	kdb_register_flags("md", kdb_md, "<vaddr>",
 	  "Display Memory Contents, also mdWcN, e.g. md8c1", 1,
-			    KDB_REPEAT_NO_ARGS);
-	kdb_register_repeat("mdr", kdb_md, "<vaddr> <bytes>",
-	  "Display Raw Memory", 0, KDB_REPEAT_NO_ARGS);
-	kdb_register_repeat("mdp", kdb_md, "<paddr> <bytes>",
-	  "Display Physical Memory", 0, KDB_REPEAT_NO_ARGS);
-	kdb_register_repeat("mds", kdb_md, "<vaddr>",
-	  "Display Memory Symbolically", 0, KDB_REPEAT_NO_ARGS);
-	kdb_register_repeat("mm", kdb_mm, "<vaddr> <contents>",
-	  "Modify Memory Contents", 0, KDB_REPEAT_NO_ARGS);
-	kdb_register_repeat("go", kdb_go, "[<vaddr>]",
-	  "Continue Execution", 1, KDB_REPEAT_NONE);
-	kdb_register_repeat("rd", kdb_rd, "",
-	  "Display Registers", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("rm", kdb_rm, "<reg> <contents>",
-	  "Modify Registers", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("ef", kdb_ef, "<vaddr>",
-	  "Display exception frame", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("bt", kdb_bt, "[<vaddr>]",
-	  "Stack traceback", 1, KDB_REPEAT_NONE);
-	kdb_register_repeat("btp", kdb_bt, "<pid>",
-	  "Display stack for process <pid>", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("bta", kdb_bt, "[D|R|S|T|C|Z|E|U|I|M|A]",
-	  "Backtrace all processes matching state flag", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("btc", kdb_bt, "",
-	  "Backtrace current process on each cpu", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("btt", kdb_bt, "<vaddr>",
+	  KDB_ENABLE_MEM_READ | KDB_REPEAT_NO_ARGS);
+	kdb_register_flags("mdr", kdb_md, "<vaddr> <bytes>",
+	  "Display Raw Memory", 0,
+	  KDB_ENABLE_MEM_READ | KDB_REPEAT_NO_ARGS);
+	kdb_register_flags("mdp", kdb_md, "<paddr> <bytes>",
+	  "Display Physical Memory", 0,
+	  KDB_ENABLE_MEM_READ | KDB_REPEAT_NO_ARGS);
+	kdb_register_flags("mds", kdb_md, "<vaddr>",
+	  "Display Memory Symbolically", 0,
+	  KDB_ENABLE_MEM_READ | KDB_REPEAT_NO_ARGS);
+	kdb_register_flags("mm", kdb_mm, "<vaddr> <contents>",
+	  "Modify Memory Contents", 0,
+	  KDB_ENABLE_MEM_WRITE | KDB_REPEAT_NO_ARGS);
+	kdb_register_flags("go", kdb_go, "[<vaddr>]",
+	  "Continue Execution", 1,
+	  KDB_ENABLE_REG_WRITE | KDB_ENABLE_ALWAYS_SAFE_NO_ARGS);
+	kdb_register_flags("rd", kdb_rd, "",
+	  "Display Registers", 0,
+	  KDB_ENABLE_REG_READ);
+	kdb_register_flags("rm", kdb_rm, "<reg> <contents>",
+	  "Modify Registers", 0,
+	  KDB_ENABLE_REG_WRITE);
+	kdb_register_flags("ef", kdb_ef, "<vaddr>",
+	  "Display exception frame", 0,
+	  KDB_ENABLE_MEM_READ);
+	kdb_register_flags("bt", kdb_bt, "[<vaddr>]",
+	  "Stack traceback", 1,
+	  KDB_ENABLE_MEM_READ | KDB_ENABLE_INSPECT_NO_ARGS);
+	kdb_register_flags("btp", kdb_bt, "<pid>",
+	  "Display stack for process <pid>", 0,
+	  KDB_ENABLE_INSPECT);
+	kdb_register_flags("bta", kdb_bt, "[D|R|S|T|C|Z|E|U|I|M|A]",
+	  "Backtrace all processes matching state flag", 0,
+	  KDB_ENABLE_INSPECT);
+	kdb_register_flags("btc", kdb_bt, "",
+	  "Backtrace current process on each cpu", 0,
+	  KDB_ENABLE_INSPECT);
+	kdb_register_flags("btt", kdb_bt, "<vaddr>",
 	  "Backtrace process given its struct task address", 0,
-			    KDB_REPEAT_NONE);
-	kdb_register_repeat("env", kdb_env, "",
-	  "Show environment variables", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("set", kdb_set, "",
-	  "Set environment variables", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("help", kdb_help, "",
-	  "Display Help Message", 1, KDB_REPEAT_NONE);
-	kdb_register_repeat("?", kdb_help, "",
-	  "Display Help Message", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("cpu", kdb_cpu, "<cpunum>",
-	  "Switch to new cpu", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("kgdb", kdb_kgdb, "",
-	  "Enter kgdb mode", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("ps", kdb_ps, "[<flags>|A]",
-	  "Display active task list", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("pid", kdb_pid, "<pidnum>",
-	  "Switch to another task", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("reboot", kdb_reboot, "",
-	  "Reboot the machine immediately", 0, KDB_REPEAT_NONE);
+	  KDB_ENABLE_MEM_READ | KDB_ENABLE_INSPECT_NO_ARGS);
+	kdb_register_flags("env", kdb_env, "",
+	  "Show environment variables", 0,
+	  KDB_ENABLE_ALWAYS_SAFE);
+	kdb_register_flags("set", kdb_set, "",
+	  "Set environment variables", 0,
+	  KDB_ENABLE_ALWAYS_SAFE);
+	kdb_register_flags("help", kdb_help, "",
+	  "Display Help Message", 1,
+	  KDB_ENABLE_ALWAYS_SAFE);
+	kdb_register_flags("?", kdb_help, "",
+	  "Display Help Message", 0,
+	  KDB_ENABLE_ALWAYS_SAFE);
+	kdb_register_flags("cpu", kdb_cpu, "<cpunum>",
+	  "Switch to new cpu", 0,
+	  KDB_ENABLE_ALWAYS_SAFE_NO_ARGS);
+	kdb_register_flags("kgdb", kdb_kgdb, "",
+	  "Enter kgdb mode", 0, 0);
+	kdb_register_flags("ps", kdb_ps, "[<flags>|A]",
+	  "Display active task list", 0,
+	  KDB_ENABLE_INSPECT);
+	kdb_register_flags("pid", kdb_pid, "<pidnum>",
+	  "Switch to another task", 0,
+	  KDB_ENABLE_INSPECT);
+	kdb_register_flags("reboot", kdb_reboot, "",
+	  "Reboot the machine immediately", 0,
+	  KDB_ENABLE_REBOOT);
 #if defined(CONFIG_MODULES)
-	kdb_register_repeat("lsmod", kdb_lsmod, "",
-	  "List loaded kernel modules", 0, KDB_REPEAT_NONE);
+	kdb_register_flags("lsmod", kdb_lsmod, "",
+	  "List loaded kernel modules", 0,
+	  KDB_ENABLE_INSPECT);
 #endif
 #if defined(CONFIG_MAGIC_SYSRQ)
-	kdb_register_repeat("sr", kdb_sr, "<key>",
-	  "Magic SysRq key", 0, KDB_REPEAT_NONE);
+	kdb_register_flags("sr", kdb_sr, "<key>",
+	  "Magic SysRq key", 0,
+	  KDB_ENABLE_ALWAYS_SAFE);
 #endif
 #if defined(CONFIG_PRINTK)
-	kdb_register_repeat("dmesg", kdb_dmesg, "[lines]",
-	  "Display syslog buffer", 0, KDB_REPEAT_NONE);
+	kdb_register_flags("dmesg", kdb_dmesg, "[lines]",
+	  "Display syslog buffer", 0,
+	  KDB_ENABLE_ALWAYS_SAFE);
 #endif
 	if (arch_kgdb_ops.enable_nmi) {
-		kdb_register_repeat("disable_nmi", kdb_disable_nmi, "",
-		  "Disable NMI entry to KDB", 0, KDB_REPEAT_NONE);
-	}
-	kdb_register_repeat("defcmd", kdb_defcmd, "name \"usage\" \"help\"",
-	  "Define a set of commands, down to endefcmd", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("kill", kdb_kill, "<-signal> <pid>",
-	  "Send a signal to a process", 0, KDB_REPEAT_NONE);
-	kdb_register_repeat("summary", kdb_summary, "",
-	  "Summarize the system", 4, KDB_REPEAT_NONE);
-	kdb_register_repeat("per_cpu", kdb_per_cpu, "<sym> [<bytes>] [<cpu>]",
-	  "Display per_cpu variables", 3, KDB_REPEAT_NONE);
-	kdb_register_repeat("grephelp", kdb_grep_help, "",
-	  "Display help on | grep", 0, KDB_REPEAT_NONE);
+		kdb_register_flags("disable_nmi", kdb_disable_nmi, "",
+		  "Disable NMI entry to KDB", 0,
+		  KDB_ENABLE_ALWAYS_SAFE);
+	}
+	kdb_register_flags("defcmd", kdb_defcmd, "name \"usage\" \"help\"",
+	  "Define a set of commands, down to endefcmd", 0,
+	  KDB_ENABLE_ALWAYS_SAFE);
+	kdb_register_flags("kill", kdb_kill, "<-signal> <pid>",
+	  "Send a signal to a process", 0,
+	  KDB_ENABLE_SIGNAL);
+	kdb_register_flags("summary", kdb_summary, "",
+	  "Summarize the system", 4,
+	  KDB_ENABLE_ALWAYS_SAFE);
+	kdb_register_flags("per_cpu", kdb_per_cpu, "<sym> [<bytes>] [<cpu>]",
+	  "Display per_cpu variables", 3,
+	  KDB_ENABLE_MEM_READ);
+	kdb_register_flags("grephelp", kdb_grep_help, "",
+	  "Display help on | grep", 0,
+	  KDB_ENABLE_ALWAYS_SAFE);
 }
 
 /* Execute any commands defined in kdb_cmds.  */
diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
index 7afd3c8c41d5..eaacd1693954 100644
--- a/kernel/debug/kdb/kdb_private.h
+++ b/kernel/debug/kdb/kdb_private.h
@@ -172,10 +172,9 @@ typedef struct _kdbtab {
 	kdb_func_t cmd_func;		/* Function to execute command */
 	char    *cmd_usage;		/* Usage String for this command */
 	char    *cmd_help;		/* Help message for this command */
-	short    cmd_flags;		/* Parsing flags */
 	short    cmd_minlen;		/* Minimum legal # command
 					 * chars required */
-	kdb_repeat_t cmd_repeat;	/* Does command auto repeat on enter? */
+	kdb_cmdflags_t cmd_flags;	/* Command behaviour flags */
 } kdbtab_t;
 
 extern int kdb_bt(int, const char **);	/* KDB display back trace */
diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
index b0b1c44e923a..3ccf5c2c1320 100644
--- a/kernel/trace/trace_kdb.c
+++ b/kernel/trace/trace_kdb.c
@@ -132,8 +132,8 @@ static int kdb_ftdump(int argc, const char **argv)
 
 static __init int kdb_ftrace_register(void)
 {
-	kdb_register_repeat("ftdump", kdb_ftdump, "[skip_#lines] [cpu]",
-			    "Dump ftrace log", 0, KDB_REPEAT_NONE);
+	kdb_register_flags("ftdump", kdb_ftdump, "[skip_#lines] [cpu]",
+			    "Dump ftrace log", 0, KDB_ENABLE_ALWAYS_SAFE);
 	return 0;
 }
 
diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb
index 358eb81fa28d..c635a107a7de 100644
--- a/lib/Kconfig.kgdb
+++ b/lib/Kconfig.kgdb
@@ -73,6 +73,31 @@ config KGDB_KDB
 	help
 	  KDB frontend for kernel
 
+config KDB_DEFAULT_ENABLE
+	hex "KDB: Select kdb command functions to be enabled by default"
+	depends on KGDB_KDB
+	default 0x1
+	help
+	  Specifiers which kdb commands are enabled by default. This may
+	  be set to 1 or 0 to enable all commands or disable almost all
+	  commands.
+
+	  Alternatively the following bitmask applies:
+
+	    0x0002 - allow arbitrary reads from memory and symbol lookup
+	    0x0004 - allow arbitrary writes to memory
+	    0x0008 - allow current register state to be inspected
+	    0x0010 - allow current register state to be modified
+	    0x0020 - allow passive inspection (backtrace, process list, lsmod)
+	    0x0040 - allow flow control management (breakpoint, single step)
+	    0x0080 - enable signalling of processes
+	    0x0100 - allow machine to be rebooted
+
+	  The config option merely sets the default at boot time. Both
+	  issuing 'echo X > /sys/module/kdb/parameters/cmd_enable' or
+          setting with kdb.cmd_enable=X kernel command line option will
+	  override the default settings.
+
 config KDB_KEYBOARD
 	bool "KGDB_KDB: keyboard as input device"
 	depends on VT && KGDB_KDB