[PATCH] RISC-V: KVM: Reject overlapping AIA IMSIC address fields

[Pengpeng Hou]

KVM lets userspace configure the IMSIC guest, HART, group-width, and
group-shift fields independently. The individual bounds allow a layout
such as guest_bits=7, hart_bits=6, group_bits=1, and group_shift=24.

That layout places the group index bit at bit 24 while the lower
guest+HART field also extends through bit 24. The IMSIC address helpers
later consume these values as one address layout: aia_imsic_ppn() masks
the lower guest+HART field and the group field, while
aia_imsic_hart_index() combines the group and HART index. Allowing an
overlapping configuration therefore gives one address bit two different
meanings.

Reject group-index layouts that start before the end of the guest+HART
field before initializing the in-kernel irqchip.

Fixes: 89d01306e34d ("RISC-V: KVM: Implement device interface for AIA irqchip")
Signed-off-by: Pengpeng Hou <pengpeng@xxxxxxxxxxx>
---
 arch/riscv/kvm/aia_device.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/riscv/kvm/aia_device.c b/arch/riscv/kvm/aia_device.c
index be83c2d5fc308..0793d4d4cf5e3 100644
--- a/arch/riscv/kvm/aia_device.c
+++ b/arch/riscv/kvm/aia_device.c
@@ -248,6 +248,12 @@ static int aia_init(struct kvm *kvm)
 	if (aia->nr_sources && aia->aplic_addr == KVM_RISCV_AIA_UNDEF_ADDR)
 		return -EINVAL;
 
+	/* Group index bits must not overlap guest and HART index bits. */
+	if (aia->nr_group_bits &&
+	    aia->nr_group_shift < IMSIC_MMIO_PAGE_SHIFT +
+					  aia->nr_guest_bits + aia->nr_hart_bits)
+		return -EINVAL;
+
 	/* Initialize APLIC */
 	ret = kvm_riscv_aia_aplic_init(kvm);
 	if (ret)
-- 
2.43.0