diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 7064a1b55bf87..1e6cd3a806521 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -628,6 +628,29 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 				continue;
 			kgdb_connected = 0;
 		} else {
+			/*
+			 * This is a brutal way to interfere with the debugger
+			 * and prevent gdb being used to poke at kernel memory.
+			 * This could cause trouble if lockdown is applied when
+			 * there is already an active gdb session. For now the
+			 * answer is simply "don't do that". Typically lockdown
+			 * *will* be applied before the debug core gets started
+			 * so only developers using kgdb for fairly advanced
+			 * early kernel debug can be biten by this. Hopefully
+			 * they are sophisticated enough to take care of
+			 * themselves, especially with help from the lockdown
+			 * message printed on the console!
+			 */
+			if (kernel_is_locked_down("use of kgdb/kdb to write kernel RAM")) {
+				if (IS_ENABLED(CONFIG_KGDB_KDB)) {
+					/* Switch back to kdb if possible... */
+					dbg_kdb_mode = 1;
+					continue;
+				} else {
+					/* ... otherwise just bail */
+					break;
+				}
+			}
 			error = gdb_serial_stub(ks);
 		}
 
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index d5c7f02f6fbaa..067da080c5153 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -168,10 +168,62 @@ 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.
+ * Update the permissions flags (kdb_cmd_enabled) to match the
+ * current lockdown state.
+ *
+ * Within this function the calls to security_locked_down() are "lazy". We
+ * avoid calling them if the current value of kdb_cmd_enabled already excludes
+ * flags that might be subject to lockdown. Additionally we deliberately check
+ * the lockdown flags independently (even though read lockdown implies write
+ * lockdown) since that results in both simpler code and clearer messages to
+ * the user on first-time debugger entry.
+ *
+ * The permission masks during a read+write lockdown permits the following
+ * flags: INSPECT, SIGNAL, REBOOT (and ALWAYS_SAFE).
+ *
+ * The INSPECT commands are not blocked during lockdown because they are
+ * not arbitrary memory reads. INSPECT covers the backtrace family (sometimes
+ * forcing them to have no arguments) and lsmod. These commands do expose
+ * some kernel state but do not allow the developer seated at the console to
+ * choose what state is reported. SIGNAL and REBOOT should not be controversial,
+ * given these are allowed for root during lockdown already.
+ */
+static void kdb_check_for_lockdown(void)
+{
+	const int write_flags = KDB_ENABLE_MEM_WRITE |
+				KDB_ENABLE_REG_WRITE |
+				KDB_ENABLE_FLOW_CTRL;
+	const int read_flags = KDB_ENABLE_MEM_READ |
+			       KDB_ENABLE_REG_READ;
+
+	bool need_to_lockdown_write = false;
+	bool need_to_lockdown_read = false;
+
+	if (kdb_cmd_enabled & (KDB_ENABLE_ALL | write_flags))
+		need_to_lockdown_write =
+			kernel_is_locked_down("use of kgdb/kdb to write kernel RAM");
+
+	if (kdb_cmd_enabled & (KDB_ENABLE_ALL | read_flags))
+		need_to_lockdown_read =
+			kernel_is_locked_down("use of kgdb/kdb to read kernel RAM");
+
+	/* De-compose KDB_ENABLE_ALL if required */
+	if (need_to_lockdown_write || need_to_lockdown_read)
+		if (kdb_cmd_enabled & KDB_ENABLE_ALL)
+			kdb_cmd_enabled = KDB_ENABLE_MASK & ~KDB_ENABLE_ALL;
+
+	if (need_to_lockdown_write)
+		kdb_cmd_enabled &= ~write_flags;
+
+	if (need_to_lockdown_read)
+		kdb_cmd_enabled &= ~read_flags;
+}
+
+/*
+ * Check whether the flags of the current command, the permissions of the kdb
+ * console and the lockdown state allow a command to be run.
  */
-static inline bool kdb_check_flags(kdb_cmdflags_t flags, int permissions,
+static bool kdb_check_flags(kdb_cmdflags_t flags, int permissions,
 				   bool no_args)
 {
 	/* permissions comes from userspace so needs massaging slightly */
@@ -1169,6 +1221,9 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs,
 		kdb_curr_task(raw_smp_processor_id());
 
 	KDB_DEBUG_STATE("kdb_local 1", reason);
+
+	kdb_check_for_lockdown();
+
 	kdb_go_count = 0;
 	if (reason == KDB_REASON_DEBUG) {
 		/* special case below */