[PATCH] - TPM device driver layer (tpm.c|h)

[Richard MUSIL <richard.musil@st.com>]

Dear all,

I am currently writing virtual TPM device driver. This driver exposes
itself and behaves like regular TPM device (i.e. uses TPM layer which is
already present in kernel), but instead of talking to hardware it talks
to user space.

In my setup, I can create several virtual devices and delete them in
runtime. During this I noticed that current implementation is prone to
segfault when tpm_remove_hardware is called while the device is in its
receiving routine.

The problem is in tpm_remove_hardware which does all necessary steps to
remove the device, but it does not wait for the device being actually
removed and kfrees tpm_chip struct right away. If the device is at this
time in its receiving routine (through read call, for example) it blocks
the device removal until the call is completed. The call cannot be
completed though because tpm_chip struct was already kfreed.

Since there is significant timeout and it is possible to meet that
timeout in normal operation this situation is quite easily reproducible.

What I present below is rather quickfix with least impact on other TPM
parts (drivers). The patch uses device->remove callback (of
platform_device device) and reroutes this to itself. In this
callback it eventually calls vendor callback and finally kfrees all
memory resources allocated on its own.

The correct solution for this I believe would require removing TPM
hardware (as it is done by tpm_remove_hardware right now) in two steps
both called by vendor driver. In the first one vendor driver will just
"unregister" the hardware. In the second step vendor driver will call
tpm_release_resources routine which kfrees all resources allocated by
tpm.c. In order to be able to call tpm_release_resources, vendor driver
will have to register as platform driver and handle
platform_driver.probe and platform_driver.remove.

This will however require some changes in all drivers, which I cannot
test (but I could eventually write the patch). Also I see some "issues"
in tpm_tis which will have to be clarified.

--
Richard


>From bd80b63ca2e1edb761a3ffcf87bd86c30a44ca5f Mon Sep 17 00:00:00 2001
From: Richard Musil <richard.musil@st.com>
Date: Tue, 21 Aug 2007 16:46:06 +0200
Subject: [PATCH] Change in TPM module:

The clean up procedure now uses platform device "release" callback to
handle memory clean up. For this purpose "release" function callback was
added to struct tpm_vendor_specific, so hw device driver provider can get
called when it is safe to remove all allocated resources.

This is supposed to fix a bug in device removal, where device while in
receive function (waiting on timeout) was prone to segfault, if the
tpm_chip struct was unallocated before the timeout expired (in
tpm_remove_hardware).
---
 drivers/char/tpm/tpm.c |   46 +++++++++++++++++++++++++++++-----------------
 drivers/char/tpm/tpm.h |    2 ++
 2 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
index 9bb5429..41eba7e 100644
--- a/drivers/char/tpm/tpm.c
+++ b/drivers/char/tpm/tpm.c
@@ -1031,18 +1031,13 @@ void tpm_remove_hardware(struct device *dev)
 
 	spin_unlock(&driver_lock);
 
-	dev_set_drvdata(dev, NULL);
 	misc_deregister(&chip->vendor.miscdev);
-	kfree(chip->vendor.miscdev.name);
 
 	sysfs_remove_group(&dev->kobj, chip->vendor.attr_group);
 	tpm_bios_log_teardown(chip->bios_dir);
 
-	clear_bit(chip->dev_num, dev_mask);
-
-	kfree(chip);
-
-	put_device(dev);
+	/* write it this way to be explicit (chip->dev == dev) */
+	put_device(chip->dev);
 }
 EXPORT_SYMBOL_GPL(tpm_remove_hardware);
 
@@ -1083,6 +1078,28 @@ int tpm_pm_resume(struct device *dev)
 EXPORT_SYMBOL_GPL(tpm_pm_resume);
 
 /*
+ * Once all references to platform device are down to 0,
+ * release all allocated structures.
+ * In case vendor provided release function,
+ * call it too.
+ */
+static void tpm_dev_release(struct device *dev)
+{
+	struct tpm_chip *chip = dev_get_drvdata(dev);
+	/* call vendor release, if defined */
+	if (chip->vendor.release)
+		chip->vendor.release(dev);
+
+	/* it *should* be: chip->release != NULL */
+	if (likely(chip->release))
+		chip->release(dev);
+
+	clear_bit(chip->dev_num, dev_mask);
+	kfree(chip->vendor.miscdev.name);
+	kfree(chip);
+}
+
+/*
  * Called from tpm_<specific>.c probe function only for devices 
  * the driver has determined it should claim.  Prior to calling
  * this function the specific probe function has called pci_enable_device
@@ -1136,23 +1153,21 @@ struct tpm_chip *tpm_register_hardware(struct device *dev, const struct tpm_vend
 
 	chip->vendor.miscdev.parent = dev;
 	chip->dev = get_device(dev);
+	chip->release = dev->release;
+	dev->release = tpm_dev_release;
+	dev_set_drvdata(dev, chip);
 
 	if (misc_register(&chip->vendor.miscdev)) {
 		dev_err(chip->dev,
 			"unable to misc_register %s, minor %d\n",
 			chip->vendor.miscdev.name,
 			chip->vendor.miscdev.minor);
-		put_device(dev);
-		clear_bit(chip->dev_num, dev_mask);
-		kfree(chip);
-		kfree(devname);
+		put_device(chip->dev);
 		return NULL;
 	}
 
 	spin_lock(&driver_lock);
 
-	dev_set_drvdata(dev, chip);
-
 	list_add(&chip->list, &tpm_chip_list);
 
 	spin_unlock(&driver_lock);
@@ -1160,10 +1175,7 @@ struct tpm_chip *tpm_register_hardware(struct device *dev, const struct tpm_vend
 	if (sysfs_create_group(&dev->kobj, chip->vendor.attr_group)) {
 		list_del(&chip->list);
 		misc_deregister(&chip->vendor.miscdev);
-		put_device(dev);
-		clear_bit(chip->dev_num, dev_mask);
-		kfree(chip);
-		kfree(devname);
+		put_device(chip->dev);
 		return NULL;
 	}
 
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index b2e2b00..f1c265e 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -74,6 +74,7 @@ struct tpm_vendor_specific {
 	int (*send) (struct tpm_chip *, u8 *, size_t);
 	void (*cancel) (struct tpm_chip *);
 	u8 (*status) (struct tpm_chip *);
+	void (*release) (struct device *);
 	struct miscdevice miscdev;
 	struct attribute_group *attr_group;
 	struct list_head list;
@@ -106,6 +107,7 @@ struct tpm_chip {
 	struct dentry **bios_dir;
 
 	struct list_head list;
+	void (*release) (struct device *);
 };
 
 #define to_tpm_chip(n) container_of(n, struct tpm_chip, vendor)
-- 
1.5.3.rc5


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