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Message-ID: <a75f9231-b347-cec1-e7af-7bbed4ad2f00@chromium.org>
Date: Mon, 27 Jul 2020 22:28:20 +0200
From: KP Singh <kpsingh@...omium.org>
To: Martin KaFai Lau <kafai@...com>
Cc: linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
linux-security-module@...r.kernel.org,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Paul Turner <pjt@...gle.com>, Jann Horn <jannh@...gle.com>,
Florent Revest <revest@...omium.org>
Subject: Re: [PATCH bpf-next v6 3/7] bpf: Generalize bpf_sk_storage
On 25.07.20 03:13, Martin KaFai Lau wrote:
> On Thu, Jul 23, 2020 at 01:50:28PM +0200, KP Singh wrote:
>> From: KP Singh <kpsingh@...gle.com>
>>
>> Refactor the functionality in bpf_sk_storage.c so that concept of
>> storage linked to kernel objects can be extended to other objects like
>> inode, task_struct etc.
>>
>> Each new local storage will still be a separate map and provide its own
>> set of helpers. This allows for future object specific extensions and
>> still share a lot of the underlying implementation.
>>
>
> [ ... ]
>
>> @@ -386,54 +407,28 @@ static int sk_storage_alloc(struct sock *sk,
>> * Otherwise, it will become a leak (and other memory issues
>> * during map destruction).
>> */
>> -static struct bpf_local_storage_data *
>> -bpf_local_storage_update(struct sock *sk, struct bpf_map *map, void *value,
>> +struct bpf_local_storage_data *
>> +bpf_local_storage_update(void *owner, struct bpf_map *map,
>> + struct bpf_local_storage *local_storage, void *value,
>> u64 map_flags)
>> {
>> struct bpf_local_storage_data *old_sdata = NULL;
>> struct bpf_local_storage_elem *selem;
>> - struct bpf_local_storage *local_storage;
>> struct bpf_local_storage_map *smap;
>> int err;
>>
>> - /* BPF_EXIST and BPF_NOEXIST cannot be both set */
>> - if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
>> - /* BPF_F_LOCK can only be used in a value with spin_lock */
>> - unlikely((map_flags & BPF_F_LOCK) && !map_value_has_spin_lock(map)))
>> - return ERR_PTR(-EINVAL);
>> -
>> smap = (struct bpf_local_storage_map *)map;
>> - local_storage = rcu_dereference(sk->sk_bpf_storage);
>> - if (!local_storage || hlist_empty(&local_storage->list)) {
>> - /* Very first elem for this object */
>> - err = check_flags(NULL, map_flags);
> This check_flags here is missing in the later sk_storage_update().
>
>> - if (err)
>> - return ERR_PTR(err);
>> -
>> - selem = bpf_selem_alloc(smap, sk, value, true);
>> - if (!selem)
>> - return ERR_PTR(-ENOMEM);
>> -
>> - err = sk_storage_alloc(sk, smap, selem);
>> - if (err) {
>> - kfree(selem);
>> - atomic_sub(smap->elem_size, &sk->sk_omem_alloc);
>> - return ERR_PTR(err);
>> - }
>> -
>> - return SDATA(selem);
>> - }
>>
>> if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
>> /* Hoping to find an old_sdata to do inline update
>> * such that it can avoid taking the local_storage->lock
>> * and changing the lists.
>> */
>> - old_sdata =
>> - bpf_local_storage_lookup(local_storage, smap, false);
>> + old_sdata = bpf_local_storage_lookup(local_storage, smap, false);
>> err = check_flags(old_sdata, map_flags);
>> if (err)
>> return ERR_PTR(err);
>> +
>> if (old_sdata && selem_linked_to_storage(SELEM(old_sdata))) {
>> copy_map_value_locked(map, old_sdata->data,
>> value, false);
>
> [ ... ]
>
>> +static struct bpf_local_storage_data *
>> +sk_storage_update(void *owner, struct bpf_map *map, void *value, u64 map_flags)
>> +{
>> + struct bpf_local_storage_data *old_sdata = NULL;
>> + struct bpf_local_storage_elem *selem;
>> + struct bpf_local_storage *local_storage;
>> + struct bpf_local_storage_map *smap;
>> + struct sock *sk;
>> + int err;
>> +
>> + err = bpf_local_storage_check_update_flags(map, map_flags);
>> + if (err)
>> + return ERR_PTR(err);
>> +
>> + sk = owner;
>> + local_storage = rcu_dereference(sk->sk_bpf_storage);
>> + smap = (struct bpf_local_storage_map *)map;
>> +
>> + if (!local_storage || hlist_empty(&local_storage->list)) {
>
> "check_flags(NULL, map_flags);" is gone in this refactoring.
>
> This part of code is copied into the inode_storage_update()
> in the latter patch which then has the same issue.
>
>> + /* Very first elem */
>> + selem = map->ops->map_selem_alloc(smap, owner, value, !old_sdata);
>> + if (!selem)
>> + return ERR_PTR(-ENOMEM);
>
>> static int sk_storage_map_btf_id;
>> const struct bpf_map_ops sk_storage_map_ops = {
>> - .map_alloc_check = bpf_sk_storage_map_alloc_check,
>> - .map_alloc = bpf_local_storage_map_alloc,
>> - .map_free = bpf_local_storage_map_free,
>> + .map_alloc_check = bpf_local_storage_map_alloc_check,
>> + .map_alloc = sk_storage_map_alloc,
>> + .map_free = sk_storage_map_free,
>> .map_get_next_key = notsupp_get_next_key,
>> .map_lookup_elem = bpf_fd_sk_storage_lookup_elem,
>> .map_update_elem = bpf_fd_sk_storage_update_elem,
>> .map_delete_elem = bpf_fd_sk_storage_delete_elem,
>> - .map_check_btf = bpf_sk_storage_map_check_btf,
>> + .map_check_btf = bpf_local_storage_map_check_btf,
>> .map_btf_name = "bpf_local_storage_map",
>> .map_btf_id = &sk_storage_map_btf_id,
>> + .map_selem_alloc = sk_selem_alloc,
>> + .map_local_storage_update = sk_storage_update,
>> + .map_local_storage_unlink = unlink_sk_storage,
> I think refactoring codes as map_selem_alloc, map_local_storage_update,
> and map_local_storage_unlink is not the best option. The sk and inode
> version of the above map_ops are mostly the same. Fixing the
> issue like the one mentioned above need to fix both sk, inode, and
> the future kernel-object code.
>
> The only difference is sk charge omem and inode does not.
> I have played around a little. I think adding the following three ops (pasted at
> the end) is better and should be enough for both sk and inode. The inode
> does not even have to implement the (un)charge ops at all.
>
> That should remove the duplication for the followings:
> - (sk|inode)_selem_alloc
> - (sk|inode)_storage_update
> - unlink_(sk|inode)_storage
> - (sk|inode)_storage_alloc
>
> Another bonus is the new bpf_local_storage_check_update_flags() and
> bpf_local_storage_publish() will be no longer needed too.
I really like this approach. Thank you so much!
>
> I have hacked up this patch 3 change to compiler-test out this idea.
> I will post in another email. Let me know wdy>
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -33,6 +33,9 @@ struct btf;
> struct btf_type;
> struct exception_table_entry;
> struct seq_operations;
> +struct bpf_local_storage;
> +struct bpf_local_storage_map;
> +struct bpf_local_storage_elem;
>
> extern struct idr btf_idr;
> extern spinlock_t btf_idr_lock;
> @@ -93,6 +96,13 @@ struct bpf_map_ops {
> __poll_t (*map_poll)(struct bpf_map *map, struct file *filp,
> struct poll_table_struct *pts);
>
> + /* Functions called by bpf_local_storage maps */
> + int (*map_local_storage_charge)(struct bpf_local_storage_map *smap,
> + void *owner, u32 size);
> + void (*map_local_storage_uncharge)(struct bpf_local_storage_map *smap,
> + void *owner, u32 size);
> + struct bpf_local_storage __rcu ** (*map_owner_storage_ptr)(struct bpf_local_storage_map *smap,
> + void *owner);
> /* BTF name and id of struct allocated by map_alloc */
> const char * const map_btf_name;
> int *map_btf_id;
>
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