Re: [PATCH bpf-next v2 0/4] Use correct destructor kfunc types

[Yonghong Song <yonghong.song@linux.dev>]

On 7/25/25 2:44 PM, Sami Tolvanen wrote:
> Hi folks,
>
> While running BPF self-tests with CONFIG_CFI_CLANG (Clang Control
> Flow Integrity) enabled, I ran into a couple of CFI failures
> in bpf_obj_free_fields() caused by type mismatches between
> the btf_dtor_kfunc_t function pointer type and the registered
> destructor functions.
>
> It looks like we can't change the argument type for these
> functions to match btf_dtor_kfunc_t because the verifier doesn't
> like void pointer arguments for functions used in BPF programs,
> so this series fixes the issue by adding stubs with correct types
> to use as destructors for each instance of this I found in the
> kernel tree.
>
> The last patch changes btf_check_dtor_kfuncs() to enforce the
> function type when CFI is enabled, so we don't end up registering
> destructors that panic the kernel. Perhaps this is something we
> could enforce even without CONFIG_CFI_CLANG?
>
> Sami
>
> ---
> v2:
> - Annotated the stubs with CFI_NOSEAL to fix issues with IBT
>    sealing on x86.
> - Changed __bpf_kfunc to explicit __used __retain.
>
> v1: https://lore.kernel.org/bpf/20250724223225.1481960-6-samitolvanen@google.com/
>
> ---
> Sami Tolvanen (4):
>    bpf: crypto: Use the correct destructor kfunc type
>    bpf: net_sched: Use the correct destructor kfunc type
>    selftests/bpf: Use the correct destructor kfunc type
>    bpf, btf: Enforce destructor kfunc type with CFI
>
>   kernel/bpf/btf.c                                     | 7 +++++++
>   kernel/bpf/crypto.c                                  | 9 ++++++++-
>   net/sched/bpf_qdisc.c                                | 9 ++++++++-
>   tools/testing/selftests/bpf/test_kmods/bpf_testmod.c | 9 ++++++++-
>   4 files changed, 31 insertions(+), 3 deletions(-)
>
>
> base-commit: 95993dc3039e29dabb9a50d074145d4cb757b08b

With this patch set and no CONFIG_CFI_CLANG in .config,
the bpf selftests work okay. In bpf ci, CONFIG_CFI_CLANG
is not enabled.

But if enabling CONFIG_CFI_CLANG, this patch set fixed
./test_progs run issue, but there are some test failures
like

===
test_get_linfo:FAIL:check jited_linfo[1]:ffffffffa000d581 - ffffffffa000d558 > 39
processed 4 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
#32/186  btf/line_info (No subprog):FAIL

test_get_linfo:FAIL:check jited_linfo[1]:ffffffffa000dee5 - ffffffffa000debc > 39
processed 4 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
#32/189  btf/line_info (No subprog. zero tailing line_info:FAIL

...

test_get_linfo:FAIL:check jited_linfo[1]:ffffffffa000e069 - ffffffffa000e040 > 38
processed 9 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 0
#32/202  btf/line_info (dead subprog + dead start w/ move):FAIL
#32      btf:FAIL
===

The failure probably not related to this patch, but rather related
to CONFIG_CFI_CLANG itself. I will debug this separately.