From 919f4ebc598701670e80e31573a58f1f2d2bf918 Mon Sep 17 00:00:00 2001 From: Wanpeng Li 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 Message-Id: <1614326399-5762-1-git-send-email-wanpengli@tencent.com> Signed-off-by: Paolo Bonzini --- 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 7d2dae92d638..58fa8c029867 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; -- 2.20.1