[PATCH v3 1/5] mdev: Introduce sha1 based mdev alias

[Parav Pandit]

Some vendor drivers want an identifier for an mdev device that is
shorter than the UUID, due to length restrictions in the consumers of
that identifier.

Add a callback that allows a vendor driver to request an alias of a
specified length to be generated for an mdev device. If generated,
that alias is checked for collisions.

It is an optional attribute.
mdev alias is generated using sha1 from the mdev name.

Signed-off-by: Parav Pandit <parav@xxxxxxxxxxxx>

---
Changelog:
v1->v2:
 - Kept mdev_device naturally aligned
 - Added error checking for crypt_*() calls
 - Corrected a typo from 'and' to 'an'
 - Changed return type of generate_alias() from int to char*
v0->v1:
 - Moved alias length check outside of the parent lock
 - Moved alias and digest allocation from kvzalloc to kzalloc
 - &alias[0] changed to alias
 - alias_length check is nested under get_alias_length callback check
 - Changed comments to start with an empty line
 - Fixed cleaunup of hash if mdev_bus_register() fails
 - Added comment where alias memory ownership is handed over to mdev device
 - Updated commit log to indicate motivation for this feature
---
 drivers/vfio/mdev/mdev_core.c    | 123 ++++++++++++++++++++++++++++++-
 drivers/vfio/mdev/mdev_private.h |   5 +-
 drivers/vfio/mdev/mdev_sysfs.c   |  13 ++--
 include/linux/mdev.h             |   4 +
 4 files changed, 135 insertions(+), 10 deletions(-)

diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
index b558d4cfd082..3bdff0469607 100644
--- a/drivers/vfio/mdev/mdev_core.c
+++ b/drivers/vfio/mdev/mdev_core.c
@@ -10,9 +10,11 @@
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/slab.h>
+#include <linux/mm.h>
 #include <linux/uuid.h>
 #include <linux/sysfs.h>
 #include <linux/mdev.h>
+#include <crypto/hash.h>
 
 #include "mdev_private.h"
 
@@ -27,6 +29,8 @@ static struct class_compat *mdev_bus_compat_class;
 static LIST_HEAD(mdev_list);
 static DEFINE_MUTEX(mdev_list_lock);
 
+static struct crypto_shash *alias_hash;
+
 struct device *mdev_parent_dev(struct mdev_device *mdev)
 {
 	return mdev->parent->dev;
@@ -150,6 +154,16 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops)
 	if (!ops || !ops->create || !ops->remove || !ops->supported_type_groups)
 		return -EINVAL;
 
+	if (ops->get_alias_length) {
+		unsigned int digest_size;
+		unsigned int aligned_len;
+
+		aligned_len = roundup(ops->get_alias_length(), 2);
+		digest_size = crypto_shash_digestsize(alias_hash);
+		if (aligned_len / 2 > digest_size)
+			return -EINVAL;
+	}
+
 	dev = get_device(dev);
 	if (!dev)
 		return -EINVAL;
@@ -259,6 +273,7 @@ static void mdev_device_free(struct mdev_device *mdev)
 	mutex_unlock(&mdev_list_lock);
 
 	dev_dbg(&mdev->dev, "MDEV: destroying\n");
+	kfree(mdev->alias);
 	kfree(mdev);
 }
 
@@ -269,18 +284,101 @@ static void mdev_device_release(struct device *dev)
 	mdev_device_free(mdev);
 }
 
-int mdev_device_create(struct kobject *kobj,
-		       struct device *dev, const guid_t *uuid)
+static const char *
+generate_alias(const char *uuid, unsigned int max_alias_len)
+{
+	struct shash_desc *hash_desc;
+	unsigned int digest_size;
+	unsigned char *digest;
+	unsigned int alias_len;
+	char *alias;
+	int ret;
+
+	/*
+	 * Align to multiple of 2 as bin2hex will generate
+	 * even number of bytes.
+	 */
+	alias_len = roundup(max_alias_len, 2);
+	alias = kzalloc(alias_len + 1, GFP_KERNEL);
+	if (!alias)
+		return ERR_PTR(-ENOMEM);
+
+	/* Allocate and init descriptor */
+	hash_desc = kvzalloc(sizeof(*hash_desc) +
+			     crypto_shash_descsize(alias_hash),
+			     GFP_KERNEL);
+	if (!hash_desc) {
+		ret = -ENOMEM;
+		goto desc_err;
+	}
+
+	hash_desc->tfm = alias_hash;
+
+	digest_size = crypto_shash_digestsize(alias_hash);
+
+	digest = kzalloc(digest_size, GFP_KERNEL);
+	if (!digest) {
+		ret = -ENOMEM;
+		goto digest_err;
+	}
+	ret = crypto_shash_init(hash_desc);
+	if (ret)
+		goto hash_err;
+
+	ret = crypto_shash_update(hash_desc, uuid, UUID_STRING_LEN);
+	if (ret)
+		goto hash_err;
+
+	ret = crypto_shash_final(hash_desc, digest);
+	if (ret)
+		goto hash_err;
+
+	bin2hex(alias, digest, min_t(unsigned int, digest_size, alias_len / 2));
+	/*
+	 * When alias length is odd, zero out an additional last byte
+	 * that bin2hex has copied.
+	 */
+	if (max_alias_len % 2)
+		alias[max_alias_len] = 0;
+
+	kfree(digest);
+	kvfree(hash_desc);
+	return alias;
+
+hash_err:
+	kfree(digest);
+digest_err:
+	kvfree(hash_desc);
+desc_err:
+	kfree(alias);
+	return ERR_PTR(ret);
+}
+
+int mdev_device_create(struct kobject *kobj, struct device *dev,
+		       const char *uuid_str, const guid_t *uuid)
 {
 	int ret;
 	struct mdev_device *mdev, *tmp;
 	struct mdev_parent *parent;
 	struct mdev_type *type = to_mdev_type(kobj);
+	const char *alias = NULL;
 
 	parent = mdev_get_parent(type->parent);
 	if (!parent)
 		return -EINVAL;
 
+	if (parent->ops->get_alias_length) {
+		unsigned int alias_len;
+
+		alias_len = parent->ops->get_alias_length();
+		if (alias_len) {
+			alias = generate_alias(uuid_str, alias_len);
+			if (IS_ERR(alias)) {
+				ret = PTR_ERR(alias);
+				goto alias_fail;
+			}
+		}
+	}
 	mutex_lock(&mdev_list_lock);
 
 	/* Check for duplicate */
@@ -300,6 +398,12 @@ int mdev_device_create(struct kobject *kobj,
 	}
 
 	guid_copy(&mdev->uuid, uuid);
+	mdev->alias = alias;
+	/*
+	 * At this point alias memory is owned by the mdev.
+	 * Mark it NULL, so that only mdev can free it.
+	 */
+	alias = NULL;
 	list_add(&mdev->next, &mdev_list);
 	mutex_unlock(&mdev_list_lock);
 
@@ -346,6 +450,8 @@ int mdev_device_create(struct kobject *kobj,
 	up_read(&parent->unreg_sem);
 	put_device(&mdev->dev);
 mdev_fail:
+	kfree(alias);
+alias_fail:
 	mdev_put_parent(parent);
 	return ret;
 }
@@ -406,7 +512,17 @@ EXPORT_SYMBOL(mdev_get_iommu_device);
 
 static int __init mdev_init(void)
 {
-	return mdev_bus_register();
+	int ret;
+
+	alias_hash = crypto_alloc_shash("sha1", 0, 0);
+	if (!alias_hash)
+		return -ENOMEM;
+
+	ret = mdev_bus_register();
+	if (ret)
+		crypto_free_shash(alias_hash);
+
+	return ret;
 }
 
 static void __exit mdev_exit(void)
@@ -415,6 +531,7 @@ static void __exit mdev_exit(void)
 		class_compat_unregister(mdev_bus_compat_class);
 
 	mdev_bus_unregister();
+	crypto_free_shash(alias_hash);
 }
 
 module_init(mdev_init)
diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
index 7d922950caaf..078fdaf7836e 100644
--- a/drivers/vfio/mdev/mdev_private.h
+++ b/drivers/vfio/mdev/mdev_private.h
@@ -32,6 +32,7 @@ struct mdev_device {
 	struct list_head next;
 	struct kobject *type_kobj;
 	struct device *iommu_device;
+	const char *alias;
 	bool active;
 };
 
@@ -57,8 +58,8 @@ void parent_remove_sysfs_files(struct mdev_parent *parent);
 int  mdev_create_sysfs_files(struct device *dev, struct mdev_type *type);
 void mdev_remove_sysfs_files(struct device *dev, struct mdev_type *type);
 
-int  mdev_device_create(struct kobject *kobj,
-			struct device *dev, const guid_t *uuid);
+int mdev_device_create(struct kobject *kobj, struct device *dev,
+		       const char *uuid_str, const guid_t *uuid);
 int  mdev_device_remove(struct device *dev);
 
 #endif /* MDEV_PRIVATE_H */
diff --git a/drivers/vfio/mdev/mdev_sysfs.c b/drivers/vfio/mdev/mdev_sysfs.c
index 7570c7602ab4..43afe0e80b76 100644
--- a/drivers/vfio/mdev/mdev_sysfs.c
+++ b/drivers/vfio/mdev/mdev_sysfs.c
@@ -63,15 +63,18 @@ static ssize_t create_store(struct kobject *kobj, struct device *dev,
 		return -ENOMEM;
 
 	ret = guid_parse(str, &uuid);
-	kfree(str);
 	if (ret)
-		return ret;
+		goto err;
 
-	ret = mdev_device_create(kobj, dev, &uuid);
+	ret = mdev_device_create(kobj, dev, str, &uuid);
 	if (ret)
-		return ret;
+		goto err;
 
-	return count;
+	ret = count;
+
+err:
+	kfree(str);
+	return ret;
 }
 
 MDEV_TYPE_ATTR_WO(create);
diff --git a/include/linux/mdev.h b/include/linux/mdev.h
index 0ce30ca78db0..f036fe9854ee 100644
--- a/include/linux/mdev.h
+++ b/include/linux/mdev.h
@@ -72,6 +72,9 @@ struct device *mdev_get_iommu_device(struct device *dev);
  * @mmap:		mmap callback
  *			@mdev: mediated device structure
  *			@vma: vma structure
+ * @get_alias_length:	Generate alias for the mdevs of this parent based on the
+ *			mdev device name when it returns non zero alias length.
+ *			It is optional.
  * Parent device that support mediated device should be registered with mdev
  * module with mdev_parent_ops structure.
  **/
@@ -92,6 +95,7 @@ struct mdev_parent_ops {
 	long	(*ioctl)(struct mdev_device *mdev, unsigned int cmd,
 			 unsigned long arg);
 	int	(*mmap)(struct mdev_device *mdev, struct vm_area_struct *vma);
+	unsigned int (*get_alias_length)(void);
 };
 
 /* interface for exporting mdev supported type attributes */
-- 
2.19.2