Kernel: Fix HPET validation

kernel/kernel/Timer/HPET.cpp

@@ -136,8 +136,7 @@ namespace Kernel
 		auto* header = static_cast<const ACPI::HPET*>(ACPI::ACPI::get().get_header("HPET"_sv, 0));
 		if (header == nullptr)
 			return BAN::Error::from_errno(ENODEV);
-
-		if (header->hardware_rev_id == 0)
+		if (header->length < sizeof(ACPI::HPET))
 			return BAN::Error::from_errno(EINVAL);
 
 		if (!InterruptController::get().is_using_apic() && !header->legacy_replacement_irq_routing_cable)
@@ -153,6 +152,12 @@ namespace Kernel
 
 		auto& regs = registers();
 
+		if ((regs.capabilities & 0xFF) == 0)
+		{
+			dwarnln("HPET: Invalid revision");
+			return BAN::Error::from_errno(EINVAL);
+		}
+
 #if ARCH(x86_64)
 		m_is_64bit = regs.capabilities & COUNT_SIZE_CAP;
 #else