x86/mwait-idle: Add C-states validation

Add validation for C-states specified via the "table=" module parameter.
Treat this module parameter as untrusted input and validate it thoroughly.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Link: https://patch.msgid.link/20251216080402.156988-4-dedekind1@gmail.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git be6a150829b3

Add __init to validate_cmdline_cstate(). Other adjustments to fit our env.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

xen/arch/x86/cpu/mwait-idle.c

@@ -72,6 +72,11 @@ boolean_param("mwait-idle", opt_mwait_idle);
 
 /* The maximum allowed length for the 'table' module parameter  */
 #define MAX_CMDLINE_TABLE_LEN 256
+/* Maximum allowed C-state latency */
+#define MAX_CMDLINE_LATENCY_US (5 * 1000 /* USEC_PER_MSEC */)
+/* Maximum allowed C-state target residency */
+#define MAX_CMDLINE_RESIDENCY_US (100 * 1000 /* USEC_PER_MSEC */)
+
 static char cmdline_table_str[MAX_CMDLINE_TABLE_LEN] __initdata;
 string_param("mwait-idle.table", cmdline_table_str);
 
@@ -1589,6 +1594,41 @@ static char *__init get_cmdline_field(char *args, char **field, char sep)
 	return args + i + 1;
 }
 
+/**
+ * validate_cmdline_cstate - Validate a C-state from cmdline.
+ * @state: The C-state to validate.
+ * @prev_state: The previous C-state in the table or NULL.
+ *
+ * Return: 0 if the C-state is valid or -EINVAL otherwise.
+ */
+static int __init validate_cmdline_cstate(const struct cpuidle_state *state,
+					  const struct cpuidle_state *prev_state)
+{
+	if (state->exit_latency == 0)
+		/* Exit latency 0 can only be used for the POLL state */
+		return -EINVAL;
+
+	if (state->exit_latency > MAX_CMDLINE_LATENCY_US)
+		return -EINVAL;
+
+	if (state->target_residency > MAX_CMDLINE_RESIDENCY_US)
+		return -EINVAL;
+
+	if (state->target_residency < state->exit_latency)
+		return -EINVAL;
+
+	if (!prev_state)
+		return 0;
+
+	if (state->exit_latency <= prev_state->exit_latency)
+		return -EINVAL;
+
+	if (state->target_residency <= prev_state->target_residency)
+		return -EINVAL;
+
+	return 0;
+}
+
 /**
  * cmdline_table_adjust - Adjust the C-states table with data from cmdline.
  *
@@ -1697,6 +1737,21 @@ static void __init cmdline_table_adjust(void)
 		       state->name, state->exit_latency, state->target_residency);
 	}
 
+	/* Validate the adjusted C-states */
+	for (i = 0; i < state_count; i++) {
+		const struct cpuidle_state *prev_state;
+
+		state = &cmdline_states[i];
+		prev_state = i ? &cmdline_states[i - 1] : NULL;
+
+		if (validate_cmdline_cstate(state, prev_state)) {
+			printk(XENLOG_ERR PREFIX
+			       "C-state '%s' validation failed\n",
+			       state->name);
+			goto error;
+		}
+	}
+
 	/* Copy the adjusted C-states table back */
 	for (i = 0; i < state_count; i++)
 		icpu.state_table[i] = cmdline_states[i];