RE: [PATCH net-next 07/19] vfio/mdev: Introduce sha1 based mdev alias

[Parav Pandit <parav@mellanox.com>]

> -----Original Message-----
> From: Jiri Pirko <jiri@resnulli.us>
> Sent: Friday, November 8, 2019 5:05 AM
> To: Parav Pandit <parav@mellanox.com>
> Cc: alex.williamson@redhat.com; davem@davemloft.net;
> kvm@vger.kernel.org; netdev@vger.kernel.org; Saeed Mahameed
> <saeedm@mellanox.com>; kwankhede@nvidia.com; leon@kernel.org;
> cohuck@redhat.com; Jiri Pirko <jiri@mellanox.com>; linux-
> rdma@vger.kernel.org
> Subject: Re: [PATCH net-next 07/19] vfio/mdev: Introduce sha1 based mdev
> alias
> 
> Thu, Nov 07, 2019 at 05:08:22PM CET, parav@mellanox.com 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.
> >
> >Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
> >Signed-off-by: Parav Pandit <parav@mellanox.com>
> >---
> > 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 @@
> 
> [...]
> 
> 
> >-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);
> 
> This is odd, see below.
> 
> 
> >+	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) {
> 
> I think this should be with WARN_ON. Driver should not never return such
> 0 and if it does, it's a bug.
>
Ok. will add it.
 
> Also I think this check should be extended by checking value is multiple of 2.
Do you mean driver must set alias length as always multiple of 2? Why?

> Then you can avoid the roundup() above. No need to allow even len.
Did you mean "no need to allow odd"? or? 
 
> 
> [...]
> 
> >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);
> 
> Why to pass the same thing twice? Move the guid_parse() call to the
> beginning of mdev_device_create() function.
>
Because alias should be unique and need to hold the lock while searching for duplicate.
So it is not done twice, and moving guid_parse() won't help due to need of lock.
 
> 
> > 	if (ret)
> >-		return ret;
> >+		goto err;
> >
> >-	return count;
> >+	ret = count;
> >+
> >+err:
> >+	kfree(str);
> >+	return ret;
> > }
> >
> > MDEV_TYPE_ATTR_WO(create);
> 
> [...]