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| -rw-r--r-- | Documentation/bpf/kfuncs.rst | 38 |
1 files changed, 32 insertions, 6 deletions
diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst index 7a3d9de5f315..0d2647fb358d 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -227,23 +227,49 @@ absolutely no ABI stability guarantees. As mentioned above, a nested pointer obtained from walking a trusted pointer is no longer trusted, with one exception. If a struct type has a field that is -guaranteed to be valid as long as its parent pointer is trusted, the -``BTF_TYPE_SAFE_NESTED`` macro can be used to express that to the verifier as -follows: +guaranteed to be valid (trusted or rcu, as in KF_RCU description below) as long +as its parent pointer is valid, the following macros can be used to express +that to the verifier: + +* ``BTF_TYPE_SAFE_TRUSTED`` +* ``BTF_TYPE_SAFE_RCU`` +* ``BTF_TYPE_SAFE_RCU_OR_NULL`` + +For example, + +.. code-block:: c + + BTF_TYPE_SAFE_TRUSTED(struct socket) { + struct sock *sk; + }; + +or .. code-block:: c - BTF_TYPE_SAFE_NESTED(struct task_struct) { + BTF_TYPE_SAFE_RCU(struct task_struct) { const cpumask_t *cpus_ptr; + struct css_set __rcu *cgroups; + struct task_struct __rcu *real_parent; + struct task_struct *group_leader; }; In other words, you must: -1. Wrap the trusted pointer type in the ``BTF_TYPE_SAFE_NESTED`` macro. +1. Wrap the valid pointer type in a ``BTF_TYPE_SAFE_*`` macro. -2. Specify the type and name of the trusted nested field. This field must match +2. Specify the type and name of the valid nested field. This field must match the field in the original type definition exactly. +A new type declared by a ``BTF_TYPE_SAFE_*`` macro also needs to be emitted so +that it appears in BTF. For example, ``BTF_TYPE_SAFE_TRUSTED(struct socket)`` +is emitted in the ``type_is_trusted()`` function as follows: + +.. code-block:: c + + BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct socket)); + + 2.4.5 KF_SLEEPABLE flag ----------------------- |