bpf: Reject stack arguments if tail call reachable

Tail calls are deprecated and will be replaced by indirect calls
in the future. Reject programs that combine tail calls with stack
arguments rather than adding complexity for a deprecated feature.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260513045109.2392108-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1a734ab91a31750b969624eda3f7b30b27fcdce8..a10cc045057dbc17628971f63375475fcf70ff06 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5267,14 +5267,23 @@ continue_func:
         * this info will be utilized by JIT so that we will be preserving the
         * tail call counter throughout bpf2bpf calls combined with tailcalls
         */
-       if (tail_call_reachable)
+       if (tail_call_reachable) {
                for (tmp = idx; tmp >= 0; tmp = dinfo[tmp].caller) {
                        if (subprog[tmp].is_exception_cb) {
                                verbose(env, "cannot tail call within exception cb\n");
                                return -EINVAL;
                        }
+                       if (subprog[tmp].stack_arg_cnt) {
+                               verbose(env, "tail_calls are not allowed in programs with stack args\n");
+                               return -EINVAL;
+                       }
                        subprog[tmp].tail_call_reachable = true;
                }
+       } else if (!idx && subprog[0].has_tail_call && subprog[0].stack_arg_cnt) {
+               verbose(env, "tail_calls are not allowed in programs with stack args\n");
+               return -EINVAL;
+       }
+
        if (subprog[0].tail_call_reachable)
                env->prog->aux->tail_call_reachable = true;