From 919f4ebc598701670e80e31573a58f1f2d2bf918 Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpengli@tencent.com>
Date: Fri, 26 Feb 2021 15:59:59 +0800
Subject: [PATCH] KVM: x86: hyper-v: Fix Hyper-V context null-ptr-deref
Reported by syzkaller:
KASAN: null-ptr-deref in range [0x0000000000000140-0x0000000000000147]
CPU: 1 PID: 8370 Comm: syz-executor859 Not tainted 5.11.0-syzkaller #0
RIP: 0010:synic_get arch/x86/kvm/hyperv.c:165 [inline]
RIP: 0010:kvm_hv_set_sint_gsi arch/x86/kvm/hyperv.c:475 [inline]
RIP: 0010:kvm_hv_irq_routing_update+0x230/0x460 arch/x86/kvm/hyperv.c:498
Call Trace:
kvm_set_irq_routing+0x69b/0x940 arch/x86/kvm/../../../virt/kvm/irqchip.c:223
kvm_vm_ioctl+0x12d0/0x2800 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3959
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae
Hyper-V context is lazily allocated until Hyper-V specific MSRs are accessed
or SynIC is enabled. However, the syzkaller testcase sets irq routing table
directly w/o enabling SynIC. This results in null-ptr-deref when accessing
SynIC Hyper-V context. This patch fixes it.
syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=163342ccd00000
Reported-by: syzbot+6987f3b2dbd9eda95f12@syzkaller.appspotmail.com
Fixes: 8f014550dfb1 ("KVM: x86: hyper-v: Make Hyper-V emulation enablement conditional")
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1614326399-5762-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/hyperv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 7d2dae92d6388..58fa8c0298673 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -159,7 +159,7 @@ static struct kvm_vcpu_hv_synic *synic_get(struct kvm *kvm, u32 vpidx)
struct kvm_vcpu_hv_synic *synic;
vcpu = get_vcpu_by_vpidx(kvm, vpidx);
- if (!vcpu)
+ if (!vcpu || !to_hv_vcpu(vcpu))
return NULL;
synic = to_hv_synic(vcpu);
return (synic->active) ? synic : NULL;
--
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