+static int check_ctx_reg(struct bpf_verifier_env *env,
+ const struct bpf_reg_state *reg, int regno)
+{
+ /* Access to ctx or passing it to a helper is only allowed in
+ * its original, unmodified form.
+ */
+
+ if (reg->off) {
+ verbose(env, "dereference of modified ctx ptr R%d off=%d disallowed\n",
+ regno, reg->off);
+ return -EACCES;
+ }
+
+ if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
+ char tn_buf[48];
+
+ tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
+ verbose(env, "variable ctx access var_off=%s disallowed\n", tn_buf);
+ return -EACCES;
+ }
+
+ return 0;
+}
+