bpf: mark a NULL memory argument of a call precise

check_mem_reg() allows bpf_register_is_null() for nullable arguments w/o marking the underlying scalar register precise. Hence a checkpoint created on such a path would prune against arbitrary scalar value. The argument may live on the stack rather than in a register when a call has more than MAX_BPF_FUNC_REG_ARGS arguments, hence the new mark_arg_precision() helper.

Eduard Zingerman committed 2 months ago

Commit f1e41811 parent 593c8eb1 file · +10 −1Browse files

Unified · Split

kernel/bpf/verifier.c+10−1

 	return mark_chain_precision_batch(env, env->cur_state);
 }
+static int mark_arg_precision(struct bpf_verifier_env *env, argno_t argno)
+{
+	int regno = reg_from_argno(argno);
+	if (regno >= 0)
+		return mark_chain_precision(env, regno);
+	return mark_stack_arg_precision(env, arg_idx_from_argno(argno));
+}
 static int check_outgoing_stack_args(struct bpf_verifier_env *env, struct bpf_func_state *caller,
 				     int nargs, const char *callee_name, const struct btf *btf,
 				     const struct btf_param *args)
 	int size, err = 0;
 	if (bpf_register_is_null(reg))
-		return 0;
+		return mark_arg_precision(env, argno);
 	if (known_memory)
 		*known_memory = true;