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Kumar Kartikeya Dwivedi says: ==================== Handle possible NULL trusted raw_tp arguments More context is available in [0], but the TLDR; is that the verifier incorrectly assumes that any raw tracepoint argument will always be non-NULL. This means that even when users correctly check possible NULL arguments, the verifier can remove the NULL check due to incorrect knowledge of the NULL-ness of the pointer. Secondly, kernel helpers or kfuncs taking these trusted tracepoint arguments incorrectly assume that all arguments will always be valid non-NULL. In this set, we mark raw_tp arguments as PTR_MAYBE_NULL on top of PTR_TRUSTED, but special case their behavior when dereferencing them or pointer arithmetic over them is involved. When passing trusted args to helpers or kfuncs, raw_tp programs are permitted to pass possibly NULL pointers in such cases. Any loads into such maybe NULL trusted PTR_TO_BTF_ID is promoted to a PROBE_MEM load to handle emanating page faults. The verifier will ensure NULL checks on such pointers are preserved and do not lead to dead code elimination. This new behavior is not applied when ref_obj_id is non-zero, as those pointers do not belong to raw_tp arguments, but instead acquired objects. Since helpers and kfuncs already require attention for PTR_TO_BTF_ID (non-trusted) pointers, we do not implement any protection for such cases in this patch set, and leave it as future work for an upcoming series. A selftest is included with this patch set to verify the new behavior, and it crashes the kernel without the first patch. [0]: https://lore.kernel.org/bpf/CAADnVQLMPPavJQR6JFsi3dtaaLHB816JN4HCV_TFWohJ61D+wQ@mail.gmail.com Changelog: ---------- v2 -> v3 v2: https://lore.kernel.org/bpf/20241103184144.3765700-1-memxor@gmail.com * Fix lenient check around check_ptr_to_btf_access allowing any PTR_TO_BTF_ID with PTR_MAYBE_NULL to be deref'd. * Add Juri and Jiri's Tested-by, Reviewed-by resp. v1 -> v2 v1: https://lore.kernel.org/bpf/20241101000017.3424165-1-memxor@gmail.com * Add patch to clean up users of gettid (Andrii) * Avoid nested blocks in sefltest (Andrii) * Prevent code motion optimization in selftest using barrier() ==================== Link: https://lore.kernel.org/r/20241104171959.2938862-1-memxor@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.