Re: [PATCH 5.15.y v2] bpf: ensure main program has an extable

Greg Kroah-Hartman
2023-06-29T12:10:10Z

On Wed, Jun 28, 2023 at 06:35:08PM -0700, Krister Johansen wrote:
> commit 0108a4e9f3584a7a2c026d1601b0682ff7335d95 upstream.
>
> 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>
> Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
> Tested-by: Ilya Leoshkevich <iii@linux.ibm.com>
> Link: https://lore.kernel.org/r/6de9b2f4b4724ef56efbb0339daaa66c8b68b1e7.1686616663.git.kjlx@templeofstupid.com
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
> ---
> kernel/bpf/verifier.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)

Now queued up, thanks.

greg k-h