[PATCH 9/9] x86/mwait-idle: Add C-states validation

[Jan Beulich <jbeulich@xxxxxxxx>]

From: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20251216080402.156988-4-dedekind1@xxxxxxxxx
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
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@xxxxxxxx>

--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -72,6 +72,11 @@ boolean_param("mwait-idle", opt_mwait_id
 
 /* 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(ch
 }
 
 /**
+ * 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(struct cpuidle_state *state,
+                                         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.
  *
  * Adjust the C-states table with data from the 'mwait-idle.table' parameter
@@ -1696,6 +1736,21 @@ static void __init cmdline_table_adjust(
                       state->name, state->exit_latency, 
state->target_residency);
        }
 
+       /* Validate the adjusted C-states */
+       for (i = 0; i < state_count; i++) {
+               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];