Re: [PATCH v2 1/6] mdev: Introduce sha1 based mdev alias

Yunsheng Lin
2019-08-29T12:27:15Z

On 2019/8/29 19:18, Parav Pandit wrote:
> 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@mellanox.com>
>
> ---
> 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);

It seems the mtty_alias_length in mtty.c can be set from module
parameter, and user can set a very large number, maybe limit the
max of the alias_len before calling kzalloc?

> + 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 */
>