[PATCH bpf-next 0/2] bpf: expand BPF arena kernel fault handling

[Emil Tsalapatis <emil@etsalapatis.com>]

Currently, the BPF arena fault handler protects against
a misbehaving BPF program passing an arena pointer to a
kfunc then unmapping the backing pages, causing a kernel
fault. However, it does not handle errors where the now
unmapped arena address is instead accessed by a non-BPF
path, or by a BPF program that has a different arena.
The former case is already possible in sched-ext if a
BPF program removes from the arena pages allocated
from the genpool allocator.

Keep a list of all arenas in the system and attempt to match
the kernel fault to all of them. If the fault does fall in
an arena, handle it with the already established scratch
page technique and retry the access.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>

Emil Tsalapatis (2):
  bpf: recover page faults across all arenas
  selftests/bpf: add arena fault recovery tests

 kernel/bpf/arena.c                            | 54 +++++++----
 tools/testing/selftests/bpf/Makefile          |  2 +-
 .../selftests/bpf/prog_tests/arena_fault.c    | 91 +++++++++++++++++++
 .../testing/selftests/bpf/progs/arena_fault.c | 55 +++++++++++
 .../selftests/bpf/progs/arena_fault_noarena.c | 17 ++++
 .../testing/selftests/bpf/test_kmods/Makefile |  2 +-
 .../bpf/test_kmods/bpf_test_arena_fault.c     | 55 +++++++++++
 .../bpf/test_kmods/bpf_test_arena_fault.h     | 10 ++
 8 files changed, 265 insertions(+), 21 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/arena_fault.c
 create mode 100644 tools/testing/selftests/bpf/progs/arena_fault.c
 create mode 100644 tools/testing/selftests/bpf/progs/arena_fault_noarena.c
 create mode 100644 tools/testing/selftests/bpf/test_kmods/bpf_test_arena_fault.c
 create mode 100644 tools/testing/selftests/bpf/test_kmods/bpf_test_arena_fault.h

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2.54.0