bpf: Allow kfuncs return 'void *'

Recognize return of 'void *' from kfunc as returning unknown scalar.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20240307031228.42896-2-alexei.starovoitov@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ee86e4d7d5fcc6462eb27e5c3d2d84388b18e382..9c2a36b1373b9b83934fbd0b8e8937f67a7d0abb 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12364,6 +12364,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
                                        meta.func_name);
                                return -EFAULT;
                        }
+               } else if (btf_type_is_void(ptr_type)) {
+                       /* kfunc returning 'void *' is equivalent to returning scalar */
+                       mark_reg_unknown(env, regs, BPF_REG_0);
                } else if (!__btf_type_is_struct(ptr_type)) {
                        if (!meta.r0_size) {
                                __u32 sz;