[PATCH bpf-next v8 2/6] bpf: Attribute async callback instructions to verification roots

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Asynchronous callbacks are explored as fresh frame-zero verifier states,
so normal callee-to-caller accounting cannot propagate their instruction
budget to the main or global subprogram whose verification scheduled them.

The callback exploration still happens within the same do_check_common()
invocation as that independent verification root. Record
env->insn_processed at do_check_common() entry and override the root's
inclusive count with the delta before returning. This includes all directly
and transitively scheduled asynchronous callbacks in the root's total
without maintaining a separate accounting call stack.

Static subprogram and callback totals remain local to their synchronous call
paths. Their self counts continue to account for each processed instruction
exactly once.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/verifier.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 51d754bdef5d..fced21ec2304 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -18448,6 +18448,7 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
 	struct bpf_prog_aux *aux = env->prog->aux;
 	struct bpf_verifier_state *state;
 	struct bpf_reg_state *regs;
+	u32 insn_processed = env->insn_processed;
 	int ret, i;
 
 	env->prev_linfo = NULL;
@@ -18590,6 +18591,15 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
 	if (!ret && pop_log)
 		bpf_vlog_reset(&env->log, 0);
 	free_states(env);
+
+	/*
+	 * The override is needed to account for async subprograms, which
+	 * are verified with their own set of stack frames and thus are
+	 * not accounted as callees by account_current_path().
+	 * Accumulate their total counts as total counts of the main or
+	 * global subprog hosting the async call.
+	 */
+	env->subprog_info[subprog].insns_total = env->insn_processed - insn_processed;
 	return ret;
 }
 
-- 
2.53.0