[bpf-next,v1,0/7] Add support for kptrs in more BPF maps

Message

Kumar Kartikeya Dwivedi Feb. 19, 2023, 3:52 p.m. UTC

This set adds support for kptrs in percpu hashmaps, percpu LRU hashmaps,
and local storage maps (covering sk, cgrp, task, inode). There are also
minor miscellaneous cleanups rolled in, unrelated to the set, that I
collected over time. Feel free to drop them, they have been
intentionally placed after the kptr support to ease partial application
of the series.

Tests are expanded to test more existing maps at runtime and also test
the code path for the local storage maps (which is shared by all
implementations).

A question for reviewers is what the position of the BPF runtime should
be on dealing with reference cycles that can be created by BPF programs
at runtime using this additional support. For instance, one can store
the kptr of the task in its own task local storage, creating a cycle
which prevents destruction of task local storage. Cycles can be formed
using arbitrarily long kptr ownership chains. Therefore, just preventing
storage of such kptrs in some maps is not a sufficient solution, and is
more likely to hurt usability.

There is precedence in existing runtimes which promise memory safety,
like Rust, where reference cycles and memory leaks are permitted.
However, traditionally the safety guarantees of BPF have been stronger.
Thus, more discussion and thought is invited on this topic to ensure we
cover all usage aspects.

Kumar Kartikeya Dwivedi (7):
  bpf: Support kptrs in percpu hashmap and percpu LRU hashmap
  bpf: Support kptrs in local storage maps
  bpf: Annotate data races in bpf_local_storage
  bpf: Remove unused MEM_ALLOC | PTR_TRUSTED checks
  bpf: Fix check_reg_type for PTR_TO_BTF_ID
  bpf: Wrap register invalidation with a helper
  selftests/bpf: Add more tests for kptrs in maps

 kernel/bpf/bpf_local_storage.c                |  51 ++-
 kernel/bpf/hashtab.c                          |  59 ++--
 kernel/bpf/syscall.c                          |   8 +-
 kernel/bpf/verifier.c                         |  65 ++--
 .../selftests/bpf/prog_tests/map_kptr.c       |  96 +++--
 tools/testing/selftests/bpf/progs/map_kptr.c  | 333 +++++++++++++++---
 6 files changed, 494 insertions(+), 118 deletions(-)


base-commit: 168de0233586fb06c5c5c56304aa9a928a09b0ba

Comments

Kumar Kartikeya Dwivedi Feb. 20, 2023, 2:35 p.m. UTC | #1

On Sun, 19 Feb 2023 at 16:52, Kumar Kartikeya Dwivedi <[e-mail]> wrote:
>
> This set adds support for kptrs in percpu hashmaps, percpu LRU hashmaps,
> and local storage maps (covering sk, cgrp, task, inode). There are also
> minor miscellaneous cleanups rolled in, unrelated to the set, that I
> collected over time. Feel free to drop them, they have been
> intentionally placed after the kptr support to ease partial application
> of the series.
>
> [...]

I've noticed the error in the CI, I'm trying to reproduce and fix it.