bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 74 insertions, 0 deletions

diff --git a/Documentation/crypto/intro.rst b/Documentation/crypto/intro.rst
new file mode 100644
index 000000000..9aa89ebbf
--- /dev/null
+++ b/Documentation/crypto/intro.rst
@@ -0,0 +1,74 @@
+Kernel Crypto API Interface Specification
+=========================================
+
+Introduction
+------------
+
+The kernel crypto API offers a rich set of cryptographic ciphers as well
+as other data transformation mechanisms and methods to invoke these.
+This document contains a description of the API and provides example
+code.
+
+To understand and properly use the kernel crypto API a brief explanation
+of its structure is given. Based on the architecture, the API can be
+separated into different components. Following the architecture
+specification, hints to developers of ciphers are provided. Pointers to
+the API function call documentation are given at the end.
+
+The kernel crypto API refers to all algorithms as "transformations".
+Therefore, a cipher handle variable usually has the name "tfm". Besides
+cryptographic operations, the kernel crypto API also knows compression
+transformations and handles them the same way as ciphers.
+
+The kernel crypto API serves the following entity types:
+
+-  consumers requesting cryptographic services
+
+-  data transformation implementations (typically ciphers) that can be
+   called by consumers using the kernel crypto API
+
+This specification is intended for consumers of the kernel crypto API as
+well as for developers implementing ciphers. This API specification,
+however, does not discuss all API calls available to data transformation
+implementations (i.e. implementations of ciphers and other
+transformations (such as CRC or even compression algorithms) that can
+register with the kernel crypto API).
+
+Note: The terms "transformation" and cipher algorithm are used
+interchangeably.
+
+Terminology
+-----------
+
+The transformation implementation is an actual code or interface to
+hardware which implements a certain transformation with precisely
+defined behavior.
+
+The transformation object (TFM) is an instance of a transformation
+implementation. There can be multiple transformation objects associated
+with a single transformation implementation. Each of those
+transformation objects is held by a crypto API consumer or another
+transformation. Transformation object is allocated when a crypto API
+consumer requests a transformation implementation. The consumer is then
+provided with a structure, which contains a transformation object (TFM).
+
+The structure that contains transformation objects may also be referred
+to as a "cipher handle". Such a cipher handle is always subject to the
+following phases that are reflected in the API calls applicable to such
+a cipher handle:
+
+1. Initialization of a cipher handle.
+
+2. Execution of all intended cipher operations applicable for the handle
+   where the cipher handle must be furnished to every API call.
+
+3. Destruction of a cipher handle.
+
+When using the initialization API calls, a cipher handle is created and
+returned to the consumer. Therefore, please refer to all initialization
+API calls that refer to the data structure type a consumer is expected
+to receive and subsequently to use. The initialization API calls have
+all the same naming conventions of crypto_alloc\*.
+
+The transformation context is private data associated with the
+transformation object.