Merge branch 'introduce-kfuncs-for-memory-reads-into-dynptrs'

Mykyta Yatsenko says:

====================
Introduce kfuncs for memory reads into dynptrs

From: Mykyta Yatsenko <yatsenko@meta.com>

This patch adds new kfuncs that enable reading variable-length
user or kernel data directly into dynptrs.
These kfuncs provide a way to perform dynamically-sized reads
while maintaining memory safety. Unlike existing
`bpf_probe_read_{user|kernel}` APIs, which are limited to constant-sized
reads, these new kfuncs allow for more flexible data access.

v4 -> v5
 * Fix pointers annotations, use __user where necessary, cast where needed

v3 -> v4
 * Added pid filtering in selftests

v2 -> v3
 * Add KF_TRUSTED_ARGS for kfuncs that take pointer to task_struct
 as an argument
 * Remove checks for non-NULL task, where it was not necessary
 * Added comments on constants used in selftests, etc.

v1 -> v2
 * Renaming helper functions to use "user_str" instead of "user_data_str"
 suffix

====================

Link: https://patch.msgid.link/20250512205348.191079-1-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>