soc/intel/common: add generic gpio lock mechanism

For added security, there are some gpios that an SoC will want to lock
once initially configured, such as gpios attached to non-host (x86)
controllers, so that they can't be recofigured at a later point in
time by rogue code.

Likewise, a mainboard may have some gpios connected to secure busses
and/or devices that they want to protect from being changed post
initial configuration.

This change adds a generic gpio locking mechanism that allows the SoC
to export a list of GPIOs to be locked down and allows the mainboard
to export a list of GPIOs that it wants locked down once
initialization is complete.

Use the SOC_INTEL_COMMON_BLOCK_SMM_LOCK_GPIO_PADS Kconfig option to
enable this feature.

BUG=b:201430600
TEST='emerge-brya coreboot chromeos-bootimage', flash and verify
brya0 boots successfully to kernel.

Signed-off-by: Nick Vaccaro <nvaccaro@google.com>
Change-Id: I42979fb89567d8bcd9392da4fb8c4113ef427b14
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58351
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/soc/intel/common/block/gpio/gpio.c

@@ -447,14 +447,27 @@ int gpio_get(gpio_t gpio_num)
 	return !!(reg & PAD_CFG0_RX_STATE);
 }
 
-int gpio_lock_pad(const gpio_t pad, enum gpio_lock_action action)
+static int sideband_msg_err(int status, int response)
 {
-	const struct pad_community *comm = gpio_get_community(pad);
+	if (status || response) {
-	size_t rel_pad;
+		printk(BIOS_ERR, "%s: error status=%x response=%x\n",
-	uint16_t offset;
+				__func__, status, response);
-	uint32_t data;
+		return (status == -1) ? -1 : response;
+	}
+
+	return 0;
+}
+
+int gpio_lock_pads(const struct gpio_lock_config *pad_list, const size_t count)
+{
+	const struct pad_community *comm;
+	enum gpio_lock_action action;
+	int status, err_response = 0;
 	uint8_t response;
-	int status;
+	uint16_t offset;
+	size_t rel_pad;
+	uint32_t data;
+	gpio_t pad;
 
 	/*
 	 * FSP-S will unlock all the GPIO pads and hide the P2SB device.  With
@@ -468,23 +481,13 @@ int gpio_lock_pad(const gpio_t pad, enum gpio_lock_action action)
 		return -1;
 	}
 
-	if (!(action & GPIO_LOCK_FULL)) {
+	if ((pad_list == NULL) || (count == 0)) {
-		printk(BIOS_ERR, "%s: Error: no action specified!\n", __func__);
+		printk(BIOS_ERR, "%s: Error: pad_list null or count = 0!\n", __func__);
 		return -1;
 	}
 
-	rel_pad = relative_pad_in_comm(comm, pad);
-	offset = comm->pad_cfg_lock_offset;
-	if (!offset) {
-		printk(BIOS_ERR, "%s: Error: offset is not defined!\n", __func__);
-		return -1;
-	}
-	offset += gpio_group_index_scaled(comm, rel_pad, 2 * sizeof(uint32_t));
-
 	/* We must use the sideband interface in order to lock the pad. */
 	struct pcr_sbi_msg msg = {
-		.pid = comm->port,
-		.offset = offset,
 		.opcode = GPIO_LOCK_UNLOCK,
 		.is_posted = false,
 		.fast_byte_enable = 0xF,
@@ -494,35 +497,69 @@ int gpio_lock_pad(const gpio_t pad, enum gpio_lock_action action)
 
 	p2sb_unhide();
 
-	data = gpio_bitmask_within_group(comm, rel_pad);
+	for (int x = 0; x < count; x++) {
+		int err;
 
-	if (action & GPIO_LOCK_CONFIG) {
+		pad = pad_list[x].gpio;
-		printk(BIOS_INFO, "%s: Locking pad %d configuration\n",
+		action = pad_list[x].action;
-		       __func__, pad);
+
-		status = pcr_execute_sideband_msg(&msg, &data, &response);
+		if (!(action & GPIO_LOCK_FULL)) {
-		if (status || response) {
+			printk(BIOS_ERR, "%s: Error: no action specified for pad %d!\n",
-			printk(BIOS_ERR, "%s: error status=%x response=%x\n", __func__, status,
+					__func__, pad);
-			       response);
+			continue;
-			p2sb_hide();
-			return status == -1 ? -1 : response;
 		}
-	}
 
-	if (action & GPIO_LOCK_TX) {
+		comm = gpio_get_community(pad);
-		printk(BIOS_INFO, "%s: Locking pad %d TX state\n", __func__,
+		rel_pad = relative_pad_in_comm(comm, pad);
-		       pad);
+		offset = comm->pad_cfg_lock_offset;
-		msg.offset = msg.offset + 4;
+		if (!offset) {
-		status = pcr_execute_sideband_msg(&msg, &data, &response);
+			printk(BIOS_ERR, "%s: Error: offset not defined for pad %d!\n",
-		if (status || response) {
+					__func__, pad);
-			printk(BIOS_ERR, "%s: error status=%x response=%x\n", __func__, status,
+			continue;
-			       response);
+		}
-			p2sb_hide();
+		offset += gpio_group_index_scaled(comm, rel_pad, 2 * sizeof(uint32_t));
-			return status == -1 ? -1 : response;
+
+		data = gpio_bitmask_within_group(comm, rel_pad);
+		msg.pid = comm->port;
+		msg.offset = offset;
+
+		if (action & GPIO_LOCK_CONFIG) {
+			if (CONFIG(DEBUG_GPIO))
+				printk(BIOS_INFO, "%s: Locking pad %d configuration\n",
+						__func__, pad);
+			status = pcr_execute_sideband_msg(&msg, &data, &response);
+			if ((err = sideband_msg_err(status, response)) != 0) {
+				err_response = err;
+				continue;
+			}
+		}
+
+		if (action & GPIO_LOCK_TX) {
+			if (CONFIG(DEBUG_GPIO))
+				printk(BIOS_INFO, "%s: Locking pad %d TX state\n",
+						__func__, pad);
+			msg.offset += 4;
+			status = pcr_execute_sideband_msg(&msg, &data, &response);
+			if ((err = sideband_msg_err(status, response)) != 0) {
+				err_response = err;
+				continue;
+			}
 		}
 	}
 
 	p2sb_hide();
-	return 0;
+
+	return err_response;
+}
+
+int gpio_lock_pad(const gpio_t pad, enum gpio_lock_action action)
+{
+	const struct gpio_lock_config pads = {
+		.gpio = pad,
+		.action = action
+	};
+
+	return gpio_lock_pads(&pads, 1);
 }
 
 void gpio_set(gpio_t gpio_num, int value)

src/soc/intel/common/block/include/intelblocks/gpio.h

@@ -205,6 +205,11 @@ enum gpio_lock_action {
 	GPIO_LOCK_FULL	 = GPIO_LOCK_CONFIG | GPIO_LOCK_TX,
 };
 
+struct gpio_lock_config {
+	gpio_t			gpio;
+	enum gpio_lock_action	action;
+};
+
 /*
  * Lock a GPIO's configuration.
  *
@@ -231,6 +236,33 @@ enum gpio_lock_action {
  */
 int gpio_lock_pad(const gpio_t pad, enum gpio_lock_action action);
 
+/*
+ * gpio_lock_pads() can be used to lock an array of gpio pads, avoiding
+ * the p2sb_unhide() and p2sb_hide() calls between each gpio lock that would
+ * occur if gpio_lock_pad() were used to lock each pad in the list.
+ *
+ * @param pad_list: array of gpio_lock_config structures, one for each gpio to lock
+ * @param count: number of gpio_lock_config structs in the pad_list array
+ * @return 0 if successful,
+ * 1 - unsuccessful
+ * 2 - powered down
+ * 3 - multi-cast mixed
+ * -1 - sideband message failed or other error
+ */
+int gpio_lock_pads(const struct gpio_lock_config *pad_list, const size_t count);
+
+/*
+ * Returns an array of gpio_lock_config entries that the SoC
+ * deems security risks that should be locked down.
+ */
+const struct gpio_lock_config *soc_gpio_lock_config(size_t *num);
+
+/*
+ * Returns an array of gpio_lock_config entries that the mainboard
+ * deems security risks that should be locked down.
+ */
+const struct gpio_lock_config *mb_gpio_lock_config(size_t *num);
+
 /*
  * Returns the pmc_gpe to gpio_gpe mapping table
  *

src/soc/intel/common/block/smm/Kconfig

@@ -8,6 +8,13 @@ config SOC_INTEL_COMMON_BLOCK_SMM_IO_TRAP
 	help
 	  Intel Processor trap flag if it is supported
 
+config SOC_INTEL_COMMON_BLOCK_SMM_LOCK_GPIO_PADS
+	bool
+	help
+	  Enable locking of security-sensitive SoC and mainboard GPIOs.
+	  An SoC may provide a list of gpios to lock, and the mainboard
+	  may also provide a list of gpios to lock.
+
 config SOC_INTEL_COMMON_BLOCK_SMM_ESPI_DISABLE
 	bool
 	default n

src/soc/intel/common/block/smm/smihandler.c

@@ -311,6 +311,40 @@ static void southbridge_smi_store(
 	}
 }
 
+__weak const struct gpio_lock_config *soc_gpio_lock_config(size_t *num)
+{
+	*num = 0;
+	return NULL;
+}
+
+__weak const struct gpio_lock_config *mb_gpio_lock_config(size_t *num)
+{
+	*num = 0;
+	return NULL;
+}
+
+static void soc_lock_gpios(void)
+{
+	const struct gpio_lock_config *soc_gpios;
+	const struct gpio_lock_config *mb_gpios;
+	size_t soc_gpio_num;
+	size_t mb_gpio_num;
+
+	/* get list of gpios from SoC */
+	soc_gpios = soc_gpio_lock_config(&soc_gpio_num);
+
+	/* get list of gpios from mainboard */
+	mb_gpios = mb_gpio_lock_config(&mb_gpio_num);
+
+	/* Lock any soc requested gpios */
+	if (soc_gpio_num)
+		gpio_lock_pads(soc_gpios, soc_gpio_num);
+
+	/* Lock any mainboard requested gpios */
+	if (mb_gpio_num)
+		gpio_lock_pads(mb_gpios, mb_gpio_num);
+}
+
 static void finalize(void)
 {
 	static int finalize_done;
@@ -337,6 +371,10 @@ static void finalize(void)
 	 */
 	mainboard_smi_finalize();
 
+	/* Lock down all GPIOs that may have been requested by the SoC and/or the mainboard. */
+	if (CONFIG(SOC_INTEL_COMMON_BLOCK_SMM_LOCK_GPIO_PADS))
+		soc_lock_gpios();
+
 	/* Specific SOC SMI handler during ramstage finalize phase */
 	smihandler_soc_at_finalize();
 }