linux-kernel - Re: [PATCH v18 02/13] btf: Export bpf

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Message-ID: <CACYkzJ7or3+zwZShXC7TdzhSbN4O9wEk6KEkbRBFh85=HZ87PQ@mail.gmail.com>
Date:   Wed, 21 Sep 2022 15:43:14 +0200
From:   KP Singh <kpsingh@...nel.org>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, sdf@...gle.com, haoluo@...gle.com,
        jolsa@...nel.org, mykolal@...com, dhowells@...hat.com,
        jarkko@...nel.org, rostedt@...dmis.org, mingo@...hat.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        shuah@...nel.org, bpf@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        deso@...teo.net, memxor@...il.com,
        Roberto Sassu <roberto.sassu@...wei.com>,
        stable@...r.kernel.org, Joanne Koong <joannelkoong@...il.com>
Subject: Re: [PATCH v18 02/13] btf: Export bpf_dynptr definition

On Tue, Sep 20, 2022 at 10:01 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
>
> From: Roberto Sassu <roberto.sassu@...wei.com>
>
> eBPF dynamic pointers is a new feature recently added to upstream. It binds
> together a pointer to a memory area and its size. The internal kernel
> structure bpf_dynptr_kern is not accessible by eBPF programs in user space.
> They instead see bpf_dynptr, which is then translated to the internal
> kernel structure by the eBPF verifier.
>
> The problem is that it is not possible to include at the same time the uapi
> include linux/bpf.h and the vmlinux BTF vmlinux.h, as they both contain the
> definition of some structures/enums. The compiler complains saying that the
> structures/enums are redefined.
>
> As bpf_dynptr is defined in the uapi include linux/bpf.h, this makes it
> impossible to include vmlinux.h. However, in some cases, e.g. when using
> kfuncs, vmlinux.h has to be included. The only option until now was to
> include vmlinux.h and add the definition of bpf_dynptr directly in the eBPF
> program source code from linux/bpf.h.
>
> Solve the problem by using the same approach as for bpf_timer (which also
> follows the same scheme with the _kern suffix for the internal kernel
> structure).
>
> Add the following line in one of the dynamic pointer helpers,
> bpf_dynptr_from_mem():
>
> BTF_TYPE_EMIT(struct bpf_dynptr);
>
> Cc: stable@...r.kernel.org
> Cc: Joanne Koong <joannelkoong@...il.com>
> Fixes: 97e03f521050c ("bpf: Add verifier support for dynptrs")
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> Acked-by: Yonghong Song <yhs@...com>

I tested this out and it works, however for the BPF signing use case
where "bpf_dynptr_kern" is added to struct bpf_prog_aux one still
ends up defining the __ksym extern with bpf_dynptr_kern.

But let's discuss that when the series is posted.

Tested-by: KP Singh <kpsingh@...nel.org>