LoongArch: KVM: Validate MSI data before routing it to EIOINTC

pch_msi_set_irq() passes e->msi.data straight into eiointc_set_irq() as
the irq number. The MSI data comes from userspace, that either via a
KVM_IRQ_ROUTING_MSI entry set with KVM_SET_GSI_ROUTING (used by irqfd
and KVM_IRQ_LINE) or directly via KVM_SIGNAL_MSI, and is never checked
against EIOINTC_IRQS.

eiointc_set_irq() uses the value with __set_bit()/__clear_bit() on the
256-bit isr bitmap, eiointc_update_irq() then indexes sw_coremap[] and
the per-cpu coreisr/sw_coreisr bitmaps with it. Therefore a data value
>= 256 reads and writes memory past the end of those arrays, i.e. any
process holding a VM fd can corrupt kernel memory beyond the allocation
of loongarch_eiointc.

Reject MSI data that doesn't fit in the EIOINTC irq space. The DMSINTC
path is unaffected as it decodes the vector from the address and masks
it.

Cc: stable@vger.kernel.org
Fixes: 1928254c5c ("LoongArch: KVM: Add irqfd support")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260531140921.1B1181F00893@smtp.kernel.org/
Reviewed-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kvm/intc/pch_pic.c

@@ -78,6 +78,9 @@ int pch_msi_set_irq(struct kvm *kvm, struct kvm_kernel_irq_routing_entry *e, int
 		return dmsintc_set_irq(kvm, msg_addr, e->msi.data, level);
 	}
 
+	if (e->msi.data >= EIOINTC_IRQS)
+		return -EINVAL;
+
 	eiointc_set_irq(kvm->arch.eiointc, e->msi.data, level);
 
 	return 0;