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Date:   Mon, 19 Sep 2022 22:30:16 -0700
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Subject: Re: [PATCH v18 02/13] btf: Export bpf_dynptr definition
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To:     Roberto Sassu <roberto.sassu@huaweicloud.com>
Cc:     andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
        daniel@iogearbox.net, deso@posteo.net, dhowells@redhat.com,
        haoluo@google.com, jarkko@kernel.org, jmorris@namei.org,
        joannelkoong@gmail.com, john.fastabend@gmail.com, jolsa@kernel.org,
        keyrings@vger.kernel.org, kpsingh@kernel.org,
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        linux-security-module@vger.kernel.org, martin.lau@linux.dev,
        memxor@gmail.com, mingo@redhat.com, mykolal@fb.com,
        paul@paul-moore.com, roberto.sassu@huawei.com, rostedt@goodmis.org,
        sdf@google.com, serge@hallyn.com, shuah@kernel.org, song@kernel.org
References: <64e8ef59363bcd0f314d4e1eb7483f4dd2b7dbcf.camel@huaweicloud.com>
 <20220919142754.626564-1-roberto.sassu@huaweicloud.com>
From:   Yonghong Song <yhs@fb.com>
In-Reply-To: <20220919142754.626564-1-roberto.sassu@huaweicloud.com>
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On 9/19/22 7:27 AM, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.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@vger.kernel.org
> Cc: Joanne Koong <joannelkoong@gmail.com>
> Fixes: 97e03f521050c ("bpf: Add verifier support for dynptrs")
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Acked-by: Yonghong Song <yhs@fb.com>