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

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

On 7/24/25 3:32 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?

I tried your patch set on top of latest bpf-next. The problem
still exists with the following error:

[   71.976265] CFI failure at bpf_obj_free_fields+0x298/0x620 (target: __bpf_crypto_ctx_release+0x0/0x10; expected type: 0xc1113566)
[   71.980134] Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
...


The following is the CFI related config items:

$ grep CFI .config
CONFIG_CFI_AUTO_DEFAULT=y
CONFIG_FUNCTION_PADDING_CFI=11
CONFIG_ARCH_SUPPORTS_CFI_CLANG=y
CONFIG_ARCH_USES_CFI_TRAPS=y
CONFIG_CFI_CLANG=y
# CONFIG_CFI_ICALL_NORMALIZE_INTEGERS is not set
CONFIG_HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG=y
CONFIG_HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC=y
# CONFIG_CFI_PERMISSIVE is not set

Did I miss anything?

>
> Sami
>
> ---
>
> 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                                  | 7 ++++++-
>   net/sched/bpf_qdisc.c                                | 7 ++++++-
>   tools/testing/selftests/bpf/test_kmods/bpf_testmod.c | 7 ++++++-
>   4 files changed, 25 insertions(+), 3 deletions(-)
>
>
> base-commit: 95993dc3039e29dabb9a50d074145d4cb757b08b