From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: "Kumar Kartikeya Dwivedi" <memxor@gmail.com>
Cc: <bpf@vger.kernel.org>, "Andrii Nakryiko" <andrii@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Emil Tsalapatis" <emil@etsalapatis.com>,
"Ihor Solodrai" <ihor.solodrai@linux.dev>,
"Tejun Heo" <tj@kernel.org>, <kkd@meta.com>,
<kernel-team@meta.com>
Subject: Re: [PATCH bpf-next v3 06/15] bpf: Recognize __nullable on pointer members of kernel structs
Date: Fri, 16 Oct 2026 02:20:57 +0000 [thread overview]
Message-ID: <DM5WJQGLNLXD.37LO6XYDR7G44@gmail.com> (raw)
In-Reply-To: <CAP01T77Rt=2feJ_HgAW2eq5GntJ6-UNwAh-1cWUCsP6zJ1PQMw@mail.gmail.com>
On Fri Oct 16, 2026 at 2:04 AM UTC, Kumar Kartikeya Dwivedi wrote:
> On Fri, 16 Oct 2026 at 03:53, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
>>
>> On Fri, Oct 16, 2026 at 03:39 AM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
>> >> > Well, BTF_TYPE_SAFE_*_OR_NULL also enforces a NULL check, so not clear
>> >> > to me how using the annotation over that will break a program (see
>> >> > type_is_trusted_or_null() usage). The only difference is that this
>> >> > annotation works with type tags applied directly on the struct.
>> >>
>> >> Got it.
>> >> Can we start moving into this direction?
>> >> At least for clang compiled kernels we can drop BTF_TYPE_SAFE_*_OR_NULL ?
>> >
>> > Yeah, makes sense, I will send a set doing the conversion.
>>
>> There is one more difference to sort out first.
>> type_is_trusted_or_null() and type_is_rcu_or_null() are called only
>> when the parent is trusted or rcu.
>> fentry/fexit args are plain PTR_TO_BTF_ID, so with __nullable on
>> socket->sk
>>
>> SEC("fentry/smc_release")
>> int BPF_PROG(bpf_smc_release, struct socket *sock)
>> {
>> if (sock->sk->__sk_common.skc_state == BPF_SMC_LISTEN)
>>
>> in progs/bpf_smc.c will be rejected with
>> invalid mem access 'ptr_or_null_'.
>> what should we do?
>>
>
> The right thing might be to just strip or_null_ when walking pointers
> where bpf_may_fault_on_deref() is true (plain PTR_TO_BTF_ID and those
> with PTR_UNTRUSTED flag). That should prevent regressions for this
> case, and match behavior of the macros. It is also okay since the
> fault is handled.
>
> The plain PTR_TO_BTF_ID can also be passed into helpers, and may be
> NULL, but that's an older problem. I have plans to revisit it at some
> point and close the issue, but it requires figuring out how we can
> annotate and prevent breaking correct cases, and provide some low
> effort path for incorrect ones. This conversion can be first step in
> that process.
All makes sense to me. Thx
next prev parent reply other threads:[~2026-10-16 2:20 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-15 23:41 [PATCH bpf-next v3 00/15] Fix some arena paper cuts Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 01/15] bpf: Compute the program digest before resolving the fd_array Kumar Kartikeya Dwivedi
2026-10-16 0:28 ` bot+bpf-ci
2026-10-15 23:41 ` [PATCH bpf-next v3 02/15] selftests/bpf: Bind an exclusive map through a continuous fd_array Kumar Kartikeya Dwivedi
2026-10-15 23:53 ` sashiko-bot
2026-10-16 0:00 ` Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 03/15] libbpf: Keep the fd_array fill index out of bpf_program__clone() Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 04/15] selftests/bpf: Clone a program that calls a module kfunc Kumar Kartikeya Dwivedi
2026-10-16 0:12 ` bot+bpf-ci
2026-10-15 23:41 ` [PATCH bpf-next v3 05/15] compiler_types: Add __arena and __nullable BTF type tag qualifiers Kumar Kartikeya Dwivedi
2026-10-16 1:08 ` Alexei Starovoitov
2026-10-16 1:15 ` Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 06/15] bpf: Recognize __nullable on pointer members of kernel structs Kumar Kartikeya Dwivedi
2026-10-15 23:54 ` sashiko-bot
2026-10-16 0:00 ` Kumar Kartikeya Dwivedi
2026-10-16 1:09 ` Alexei Starovoitov
2026-10-16 1:24 ` Kumar Kartikeya Dwivedi
2026-10-16 1:31 ` Alexei Starovoitov
2026-10-16 1:39 ` Kumar Kartikeya Dwivedi
2026-10-16 1:53 ` Alexei Starovoitov
2026-10-16 2:04 ` Kumar Kartikeya Dwivedi
2026-10-16 2:20 ` Alexei Starovoitov [this message]
2026-10-15 23:41 ` [PATCH bpf-next v3 07/15] bpf: Turn loads of __arena pointer members into arena pointers Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 08/15] selftests/bpf: Test __nullable pointer members Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 09/15] selftests/bpf: Test __arena " Kumar Kartikeya Dwivedi
2026-10-16 1:11 ` Alexei Starovoitov
2026-10-16 1:39 ` Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 10/15] libbpf: Bind the arena of an object to every program in it Kumar Kartikeya Dwivedi
2026-10-16 0:28 ` bot+bpf-ci
2026-10-15 23:41 ` [PATCH bpf-next v3 11/15] selftests/bpf: Test arena binding by libbpf Kumar Kartikeya Dwivedi
2026-10-16 0:28 ` bot+bpf-ci
2026-10-15 23:41 ` [PATCH bpf-next v3 12/15] bpf: Set up the arena base only in functions that use it Kumar Kartikeya Dwivedi
2026-10-16 1:13 ` Alexei Starovoitov
2026-10-15 23:41 ` [PATCH bpf-next v3 13/15] libbpf: Render the arena type tag with its address space Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 14/15] selftests/bpf: Test the address space rendering of the arena type tag Kumar Kartikeya Dwivedi
2026-10-15 23:41 ` [PATCH bpf-next v3 15/15] selftests/bpf: Test an arena kfunc argument passed from a subprogram Kumar Kartikeya Dwivedi
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