Re: [PATCH 1/4] mdev: Introduce sha1 based mdev alias

Alex Williamson
2019-08-27T01:45:03Z

On Mon, 26 Aug 2019 15:41:16 -0500
Parav Pandit <parav@mellanox.com> wrote:

> Whenever a parent requests to generate mdev alias, generate a mdev
> alias.
> It is an optional attribute that parent can request to generate
> for each of its child mdev.
> mdev alias is generated using sha1 from the mdev name.
>
> Signed-off-by: Parav Pandit <parav@mellanox.com>
> ---
> drivers/vfio/mdev/mdev_core.c | 98 +++++++++++++++++++++++++++++++-
> drivers/vfio/mdev/mdev_private.h | 5 +-
> drivers/vfio/mdev/mdev_sysfs.c | 13 +++--
> include/linux/mdev.h | 4 ++
> 4 files changed, 111 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index b558d4cfd082..e825ff38b037 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;
> @@ -164,6 +168,18 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops)
> goto add_dev_err;
> }
>
> + 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) {
> + ret = -EINVAL;
> + goto add_dev_err;
> + }
> + }

This looks like a sanity check, it could be done outside of the
parent_list_lock, even before we get a parent device reference.

I think we're using a callback for get_alias_length() rather than a
fixed field to support the mtty module option added in patch 4, right?
Its utility is rather limited with no args. I could imagine that if a
parent wanted to generate an alias that could be incorporated into a
string with the parent device name that it would be useful to call this
with the parent device as an arg. I guess we can save that until a
user comes along though.

There doesn't seem to be anything serializing use of alias_hash.

> +
> parent = kzalloc(sizeof(*parent), GFP_KERNEL);
> if (!parent) {
> ret = -ENOMEM;
> @@ -259,6 +275,7 @@ static void mdev_device_free(struct mdev_device *mdev)
> mutex_unlock(&mdev_list_lock);
>
> dev_dbg(&mdev->dev, "MDEV: destroying\n");
> + kvfree(mdev->alias);
> kfree(mdev);
> }
>
> @@ -269,18 +286,86 @@ 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 = 0;
> +
> + /* Align to multiple of 2 as bin2hex will generate
> + * even number of bytes.
> + */

Comment style for non-networking code please.

> + alias_len = roundup(max_alias_len, 2);
> + alias = kvzalloc(alias_len + 1, GFP_KERNEL);

The size we're generating here should be small enough to just use
kzalloc(), probably below too.

> + if (!alias)
> + return NULL;
> +
> + /* Allocate and init descriptor */
> + hash_desc = kvzalloc(sizeof(*hash_desc) +
> + crypto_shash_descsize(alias_hash),
> + GFP_KERNEL);
> + if (!hash_desc)
> + goto desc_err;
> +
> + hash_desc->tfm = alias_hash;
> +
> + digest_size = crypto_shash_digestsize(alias_hash);
> +
> + digest = kvzalloc(digest_size, GFP_KERNEL);
> + if (!digest) {
> + ret = -ENOMEM;
> + goto digest_err;
> + }
> + crypto_shash_init(hash_desc);
> + crypto_shash_update(hash_desc, uuid, UUID_STRING_LEN);
> + crypto_shash_final(hash_desc, digest);
> + bin2hex(&alias[0], digest,

&alias[0], ie. alias

> + min_t(unsigned int, digest_size, alias_len / 2));
> + /* When alias length is odd, zero out and additional last byte
> + * that bin2hex has copied.
> + */
> + if (max_alias_len % 2)
> + alias[max_alias_len] = 0;

Doesn't this give us a null terminated string for odd numbers but not
even numbers? Probably best to define that we always provide a null
terminated string then we could do this unconditionally.

> +
> + kvfree(digest);
> + kvfree(hash_desc);
> + return alias;
> +
> +digest_err:
> + kvfree(hash_desc);
> +desc_err:
> + kvfree(alias);
> + return NULL;
> +}
> +
> +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);
> + unsigned int alias_len = 0;
> + const char *alias = NULL;
>
> parent = mdev_get_parent(type->parent);
> if (!parent)
> return -EINVAL;
>
> + if (parent->ops->get_alias_length)
> + alias_len = parent->ops->get_alias_length();
> + if (alias_len) {

Why isn't this nested into the branch above?

> + alias = generate_alias(uuid_str, alias_len);
> + if (!alias) {
> + ret = -ENOMEM;

Could use an ERR_PTR and propagate an errno.

> + goto alias_fail;
> + }
> + }
> +
> mutex_lock(&mdev_list_lock);
>
> /* Check for duplicate */
> @@ -300,6 +385,8 @@ int mdev_device_create(struct kobject *kobj,
> }
>
> guid_copy(&mdev->uuid, uuid);
> + mdev->alias = alias;
> + alias = NULL;

A comment justifying this null'ing might help prevent it getting culled
as some point. It appears arbitrary at first look. Thanks,

Alex

> list_add(&mdev->next, &mdev_list);
> mutex_unlock(&mdev_list_lock);
>
> @@ -346,6 +433,8 @@ int mdev_device_create(struct kobject *kobj,
> up_read(&parent->unreg_sem);
> put_device(&mdev->dev);
> mdev_fail:
> + kvfree(alias);
> +alias_fail:
> mdev_put_parent(parent);
> return ret;
> }
> @@ -406,6 +495,10 @@ EXPORT_SYMBOL(mdev_get_iommu_device);
>
> static int __init mdev_init(void)
> {
> + alias_hash = crypto_alloc_shash("sha1", 0, 0);
> + if (!alias_hash)
> + return -ENOMEM;
> +
> return mdev_bus_register();
> }
>
> @@ -415,6 +508,7 @@ 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..cf1c0d9842c6 100644
> --- a/drivers/vfio/mdev/mdev_private.h
> +++ b/drivers/vfio/mdev/mdev_private.h
> @@ -33,6 +33,7 @@ struct mdev_device {
> struct kobject *type_kobj;
> struct device *iommu_device;
> bool active;
> + const char *alias;
> };
>
> #define to_mdev_device(dev) container_of(dev, struct mdev_device, dev)
> @@ -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 */