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Date:   Thu, 8 Jun 2023 20:33:55 -0700
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Subject: Re: [PATCH bpf v3 1/2] bpf: ensure main program has an extable
To:     Krister Johansen <kjlx@templeofstupid.com>, bpf@vger.kernel.org
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
References: <cover.1686268304.git.kjlx@templeofstupid.com>
 <d0c703a2d47d3368032c65fa70297cdcb5a16da7.1686268304.git.kjlx@templeofstupid.com>
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From:   Yonghong Song <yhs@meta.com>
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On 6/8/23 5:10 PM, Krister Johansen wrote:
> When subprograms are in use, the main program is not jit'd after the
> subprograms because jit_subprogs sets a value for prog->bpf_func upon
> success.  Subsequent calls to the JIT are bypassed when this value is
> non-NULL.  This leads to a situation where the main program and its
> func[0] counterpart are both in the bpf kallsyms tree, but only func[0]
> has an extable.  Extables are only created during JIT.  Now there are
> two nearly identical program ksym entries in the tree, but only one has
> an extable.  Depending upon how the entries are placed, there's a chance
> that a fault will call search_extable on the aux with the NULL entry.
> 
> Since jit_subprogs already copies state from func[0] to the main
> program, include the extable pointer in this state duplication.
> Additionally, ensure that the copy of the main program in func[0] is not
> added to the bpf_prog_kallsyms table. Instead, let the main program get
> added later in bpf_prog_load().  This ensures there is only a single
> copy of the main program in the kallsyms table, and that its tag matches
> the tag observed by tooling like bpftool.
> 
> Cc: stable@vger.kernel.org
> Fixes: 1c2a088a6626 ("bpf: x64: add JIT support for multi-function programs")
> Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>

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