tpm: Move Linux RNG connection to hwrng

The tpm-rng.c approach is completely inconsistent with how the kernel
handles hotplug. Instead manage a hwrng device for each TPM. This will
cause the kernel to read entropy from the TPM when it is plugged in, and
allow access to the TPM rng via /dev/hwrng.

Signed-off-by: Jason Gunthorpe <jgg@ziepe.ca>
Tested-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

3 files changed, 52 insertions, 5 deletions

diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index a30352202f1f..18c81cbe4704 100644
--- a/drivers/char/tpm/Kconfig
+++ b/drivers/char/tpm/Kconfig
@@ -26,6 +26,17 @@ menuconfig TCG_TPM
 
 if TCG_TPM
 
+config HW_RANDOM_TPM
+	bool "TPM HW Random Number Generator support"
+	depends on TCG_TPM && HW_RANDOM && !(TCG_TPM=y && HW_RANDOM=m)
+	default y
+	---help---
+	  This setting exposes the TPM's Random Number Generator as a hwrng
+	  device. This allows the kernel to collect randomness from the TPM at
+	  boot, and provides the TPM randomines in /dev/hwrng.
+
+	  If unsure, say Y.
+
 config TCG_TIS_CORE
 	tristate
 	---help---
diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index bab9c14e040c..0a62c19937b6 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -27,7 +27,7 @@
 #include <linux/freezer.h>
 #include <linux/major.h>
 #include <linux/tpm_eventlog.h>
-
+#include <linux/hw_random.h>
 #include "tpm.h"
 
 DEFINE_IDR(dev_nums_idr);
@@ -392,6 +392,26 @@ static int tpm_add_legacy_sysfs(struct tpm_chip *chip)
 
 	return 0;
 }
+
+static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
+{
+	struct tpm_chip *chip = container_of(rng, struct tpm_chip, hwrng);
+
+	return tpm_get_random(chip, data, max);
+}
+
+static int tpm_add_hwrng(struct tpm_chip *chip)
+{
+	if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
+		return 0;
+
+	snprintf(chip->hwrng_name, sizeof(chip->hwrng_name),
+		 "tpm-rng-%d", chip->dev_num);
+	chip->hwrng.name = chip->hwrng_name;
+	chip->hwrng.read = tpm_hwrng_read;
+	return hwrng_register(&chip->hwrng);
+}
+
 /*
  * tpm_chip_register() - create a character device for the TPM chip
  * @chip: TPM chip to use.
@@ -424,11 +444,13 @@ int tpm_chip_register(struct tpm_chip *chip)
 
 	tpm_add_ppi(chip);
 
+	rc = tpm_add_hwrng(chip);
+	if (rc)
+		goto out_ppi;
+
 	rc = tpm_add_char_device(chip);
-	if (rc) {
-		tpm_bios_log_teardown(chip);
-		return rc;
-	}
+	if (rc)
+		goto out_hwrng;
 
 	rc = tpm_add_legacy_sysfs(chip);
 	if (rc) {
@@ -437,6 +459,14 @@ int tpm_chip_register(struct tpm_chip *chip)
 	}
 
 	return 0;
+
+out_hwrng:
+	if (IS_ENABLED(CONFIG_HW_RANDOM_TPM))
+		hwrng_unregister(&chip->hwrng);
+out_ppi:
+	tpm_bios_log_teardown(chip);
+
+	return rc;
 }
 EXPORT_SYMBOL_GPL(tpm_chip_register);
 
@@ -456,6 +486,8 @@ EXPORT_SYMBOL_GPL(tpm_chip_register);
 void tpm_chip_unregister(struct tpm_chip *chip)
 {
 	tpm_del_legacy_sysfs(chip);
+	if (IS_ENABLED(CONFIG_HW_RANDOM_TPM))
+		hwrng_unregister(&chip->hwrng);
 	tpm_bios_log_teardown(chip);
 	if (chip->flags & TPM_CHIP_FLAG_TPM2)
 		cdev_device_del(&chip->cdevs, &chip->devs);
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index 6c189174c0d3..605c0be2b8dc 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -26,6 +26,7 @@
 #include <linux/module.h>
 #include <linux/delay.h>
 #include <linux/fs.h>
+#include <linux/hw_random.h>
 #include <linux/mutex.h>
 #include <linux/sched.h>
 #include <linux/platform_device.h>
@@ -211,6 +212,9 @@ struct tpm_chip {
 	int dev_num;		/* /dev/tpm# */
 	unsigned long is_open;	/* only one allowed */
 
+	char hwrng_name[64];
+	struct hwrng hwrng;
+
 	struct mutex tpm_mutex;	/* tpm is processing */
 
 	unsigned long timeout_a; /* jiffies */