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: [email protected]
Fixes: 1c2a088a6626 ("bpf: x64: add JIT support for multi-function programs")
Signed-off-by: Krister Johansen <[email protected]>
---
kernel/bpf/verifier.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5871aa78d01a..b62d1fc0f92b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17214,9 +17214,10 @@ static int jit_subprogs(struct bpf_verifier_env *env)
}
/* finally lock prog and jit images for all functions and
- * populate kallsysm
+ * populate kallsysm. Begin at the first subprogram, since
+ * bpf_prog_load will add the kallsyms for the main program.
*/
- for (i = 0; i < env->subprog_cnt; i++) {
+ for (i = 1; i < env->subprog_cnt; i++) {
bpf_prog_lock_ro(func[i]);
bpf_prog_kallsyms_add(func[i]);
}
@@ -17242,6 +17243,7 @@ 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
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: [email protected]
> Fixes: 1c2a088a6626 ("bpf: x64: add JIT support for multi-function programs")
> Signed-off-by: Krister Johansen <[email protected]>
Acked-by: Yonghong Song <[email protected]>