thinkpad-acpi: restrict access to some firmware LEDs

Some of the ThinkPad LEDs indicate critical conditions that can cause
data loss or cause hardware damage when ignored (e.g. force-ejecting
a powered up bay; ignoring a failing battery, or empty battery; force-
undocking with the dock buses still active, etc).

On almost all ThinkPads, LED access is write-only, and the firmware
usually does fire-and-forget signaling on them, so you effectively
lose whatever message the firmware was trying to convey to the user
when you override the LED state, without any chance to restore it.

Restrict access to all LEDs that can convey important alarms, or that
could mislead the user into incorrectly operating the hardware.  This
will make the Lenovo engineers less unhappy about the whole issue.

Allow users that really want it to still control all LEDs, it is the
unaware user that we have to worry about.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 56 insertions, 20 deletions

diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c
index f003fb7c79ca..38c34c79ff35 100644
--- a/drivers/platform/x86/thinkpad_acpi.c
+++ b/drivers/platform/x86/thinkpad_acpi.c
@@ -4657,6 +4657,16 @@ static const char * const tpacpi_led_names[TPACPI_LED_NUMLEDS] = {
 	"tpacpi::unknown_led",
 	"tpacpi::standby",
 };
+#define TPACPI_SAFE_LEDS	0x0081U
+
+static inline bool tpacpi_is_led_restricted(const unsigned int led)
+{
+#ifdef CONFIG_THINKPAD_ACPI_UNSAFE_LEDS
+	return false;
+#else
+	return (TPACPI_SAFE_LEDS & (1 << led)) == 0;
+#endif
+}
 
 static int led_get_status(const unsigned int led)
 {
@@ -4694,16 +4704,20 @@ static int led_set_status(const unsigned int led,
 	switch (led_supported) {
 	case TPACPI_LED_570:
 		/* 570 */
-		if (led > 7)
+		if (unlikely(led > 7))
 			return -EINVAL;
+		if (unlikely(tpacpi_is_led_restricted(led)))
+			return -EPERM;
 		if (!acpi_evalf(led_handle, NULL, NULL, "vdd",
 				(1 << led), led_sled_arg1[ledstatus]))
 			rc = -EIO;
 		break;
 	case TPACPI_LED_OLD:
 		/* 600e/x, 770e, 770x, A21e, A2xm/p, T20-22, X20 */
-		if (led > 7)
+		if (unlikely(led > 7))
 			return -EINVAL;
+		if (unlikely(tpacpi_is_led_restricted(led)))
+			return -EPERM;
 		rc = ec_write(TPACPI_LED_EC_HLMS, (1 << led));
 		if (rc >= 0)
 			rc = ec_write(TPACPI_LED_EC_HLBL,
@@ -4714,6 +4728,10 @@ static int led_set_status(const unsigned int led,
 		break;
 	case TPACPI_LED_NEW:
 		/* all others */
+		if (unlikely(led >= TPACPI_LED_NUMLEDS))
+			return -EINVAL;
+		if (unlikely(tpacpi_is_led_restricted(led)))
+			return -EPERM;
 		if (!acpi_evalf(led_handle, NULL, NULL, "vdd",
 				led, led_led_arg1[ledstatus]))
 			rc = -EIO;
@@ -4806,6 +4824,30 @@ static void led_exit(void)
 	kfree(tpacpi_leds);
 }
 
+static int __init tpacpi_init_led(unsigned int led)
+{
+	int rc;
+
+	tpacpi_leds[led].led = led;
+
+	tpacpi_leds[led].led_classdev.brightness_set = &led_sysfs_set;
+	tpacpi_leds[led].led_classdev.blink_set = &led_sysfs_blink_set;
+	if (led_supported == TPACPI_LED_570)
+		tpacpi_leds[led].led_classdev.brightness_get =
+						&led_sysfs_get;
+
+	tpacpi_leds[led].led_classdev.name = tpacpi_led_names[led];
+
+	INIT_WORK(&tpacpi_leds[led].work, led_set_status_worker);
+
+	rc = led_classdev_register(&tpacpi_pdev->dev,
+				&tpacpi_leds[led].led_classdev);
+	if (rc < 0)
+		tpacpi_leds[led].led_classdev.name = NULL;
+
+	return rc;
+}
+
 static int __init led_init(struct ibm_init_struct *iibm)
 {
 	unsigned int i;
@@ -4839,27 +4881,21 @@ static int __init led_init(struct ibm_init_struct *iibm)
 	}
 
 	for (i = 0; i < TPACPI_LED_NUMLEDS; i++) {
-		tpacpi_leds[i].led = i;
-
-		tpacpi_leds[i].led_classdev.brightness_set = &led_sysfs_set;
-		tpacpi_leds[i].led_classdev.blink_set = &led_sysfs_blink_set;
-		if (led_supported == TPACPI_LED_570)
-			tpacpi_leds[i].led_classdev.brightness_get =
-							&led_sysfs_get;
-
-		tpacpi_leds[i].led_classdev.name = tpacpi_led_names[i];
-
-		INIT_WORK(&tpacpi_leds[i].work, led_set_status_worker);
-
-		rc = led_classdev_register(&tpacpi_pdev->dev,
-					   &tpacpi_leds[i].led_classdev);
-		if (rc < 0) {
-			tpacpi_leds[i].led_classdev.name = NULL;
-			led_exit();
-			return rc;
+		if (!tpacpi_is_led_restricted(i)) {
+			rc = tpacpi_init_led(i);
+			if (rc < 0) {
+				led_exit();
+				return rc;
+			}
 		}
 	}
 
+#ifdef CONFIG_THINKPAD_ACPI_UNSAFE_LEDS
+	if (led_supported != TPACPI_LED_NONE)
+		printk(TPACPI_NOTICE
+			"warning: userspace override of important "
+			"firmware LEDs is enabled\n");
+#endif
 	return (led_supported != TPACPI_LED_NONE)? 0 : 1;
 }