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Date:   Wed, 7 Jun 2023 14:04:31 -0700
From:   Krister Johansen <kjlx@templeofstupid.com>
To:     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,
        stable@vger.kernel.org
Subject: [PATCH bpf v2 2/2] bpf: ensure main program has an extable
Message-ID: <de425e99876dc6c344e1a4254894a3c81e71a2ec.1686166633.git.kjlx@templeofstupid.com>
References: <cover.1686166633.git.kjlx@templeofstupid.com>
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When bpf 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.  The
alternative is to skip adding the main program to the bpf_kallsyms
table, but that would mean adding a check for subprograms into the
middle of bpf_prog_load.

Cc: stable@vger.kernel.org
Fixes: 1c2a088a6626 ("bpf: x64: add JIT support for multi-function programs")
Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
---
 kernel/bpf/verifier.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5871aa78d01a..d6939db9fbf9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17242,6 +17242,7 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 	prog->jited = 1;
 	prog->bpf_func = func[0]->bpf_func;
 	prog->jited_len = func[0]->jited_len;
+	prog->aux->extable = func[0]->aux->extable;
 	prog->aux->func = func;
 	prog->aux->func_cnt = env->subprog_cnt;
 	bpf_prog_jit_attempt_done(prog);
-- 
2.25.1