linux-kernel - [PATCH 1/2] KVM: arm64: vgic: Forbid invalid userspace Redistributor accesses

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Date:   Fri, 13 Nov 2020 22:28:00 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     <kvmarm@...ts.cs.columbia.edu>, <maz@...nel.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <eric.auger@...hat.com>,
        <james.morse@....com>, <julien.thierry.kdev@...il.com>,
        <suzuki.poulose@....com>, <wanghaibin.wang@...wei.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Keqian Zhu <zhukeqian1@...wei.com>
Subject: [PATCH 1/2] KVM: arm64: vgic: Forbid invalid userspace Redistributor accesses

It's expected that users will access registers in the redistributor *if*
the RD has been initialized properly. Unfortunately userspace can be bogus
enough to access registers before setting the RD base address, and KVM
implicitly allows it (we handle the access anyway, regardless of whether
the base address is set).

Bad thing happens when we're handling the user read of GICR_TYPER. We end
up with an oops when deferencing the unset rdreg...

	gpa_t last_rdist_typer = rdreg->base + GICR_TYPER +
			(rdreg->free_index - 1) * KVM_VGIC_V3_REDIST_SIZE;

Fix this issue by informing userspace what had gone wrong (-ENXIO).

Reported-by: Keqian Zhu <zhukeqian1@...wei.com>
Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
---
 arch/arm64/kvm/vgic/vgic-mmio-v3.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
index 52d6f24f65dc..30e370585a27 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
@@ -1040,11 +1040,15 @@ int vgic_v3_dist_uaccess(struct kvm_vcpu *vcpu, bool is_write,
 int vgic_v3_redist_uaccess(struct kvm_vcpu *vcpu, bool is_write,
 			   int offset, u32 *val)
 {
+	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
 	struct vgic_io_device rd_dev = {
 		.regions = vgic_v3_rd_registers,
 		.nr_regions = ARRAY_SIZE(vgic_v3_rd_registers),
 	};
 
+	if (IS_VGIC_ADDR_UNDEF(vgic_cpu->rd_iodev.base_addr))
+		return -ENXIO;
+
 	return vgic_uaccess(vcpu, &rd_dev, is_write, offset, val);
 }
 
-- 
2.19.1