[PATCH] LoongArch: KVM: Validate MSI data before routing it to EIOINTC

[Zeng Chi]

From: Zeng Chi <zengchi@xxxxxxxxxx>

pch_msi_set_irq() passes e->msi.data straight into eiointc_set_irq() as
the irq number.  The MSI data comes from userspace, 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.  A data value >= 256
therefore reads and writes memory past the end of those arrays, i.e.
any process holding a VM fd can corrupt kernel memory beyond the
loongarch_eiointc allocation.

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.

Fixes: 1928254c5ccb ("LoongArch: KVM: Add irqfd support")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Closes: https://lore.kernel.org/all/20260531140921.1B1181F00893@xxxxxxxxxxxxxxx/
Signed-off-by: Zeng Chi <zengchi@xxxxxxxxxx>
---
 arch/loongarch/kvm/intc/pch_pic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
index e7b77705c516..81fb534ce8dd 100644
--- a/arch/loongarch/kvm/intc/pch_pic.c
+++ b/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;
-- 
2.25.1


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