static int intel_alt_er(int idx)
{
	if (!(x86_pmu.er_flags & ERF_HAS_RSP_1))
		return idx;

	if (idx == EXTRA_REG_RSP_0)
		return EXTRA_REG_RSP_1;

	if (idx == EXTRA_REG_RSP_1)
		return EXTRA_REG_RSP_0;

	return idx;
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.