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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <c7241cc9-2b20-4f32-8ae2-93f40d12fc85@linux.dev>
Date: Fri, 25 Jul 2025 09:05:31 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Sami Tolvanen <samitolvanen@...gle.com>, bpf@...r.kernel.org
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, John Fastabend <john.fastabend@...il.com>,
 KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
 Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>,
 Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 0/4] Use correct destructor kfunc types



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