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SubjectRe: [PATCH] KVM: LAPIC: Fix pv ipis use-before-initialization
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On 20/11/18 02:39, Wanpeng Li wrote:
> Reported by syzkaller:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000014
> PGD 800000040410c067 P4D 800000040410c067 PUD 40410d067 PMD 0
> Oops: 0000 [#1] PREEMPT SMP PTI
> CPU: 3 PID: 2567 Comm: poc Tainted: G OE 4.19.0-rc5 #16
> RIP: 0010:kvm_pv_send_ipi+0x94/0x350 [kvm]
> Call Trace:
> kvm_emulate_hypercall+0x3cc/0x700 [kvm]
> handle_vmcall+0xe/0x10 [kvm_intel]
> vmx_handle_exit+0xc1/0x11b0 [kvm_intel]
> vcpu_enter_guest+0x9fb/0x1910 [kvm]
> kvm_arch_vcpu_ioctl_run+0x35c/0x610 [kvm]
> kvm_vcpu_ioctl+0x3e9/0x6d0 [kvm]
> do_vfs_ioctl+0xa5/0x690
> ksys_ioctl+0x6d/0x80
> __x64_sys_ioctl+0x1a/0x20
> do_syscall_64+0x83/0x6e0
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The reason is that the apic map has not yet been initialized, the testcase
> triggers pv_send_ipi interface by vmcall which results in kvm->arch.apic_map
> is dereferenced. This patch fixes it by checking whether or not apic map is
> NULL and bailing out immediately if that is the case.
>
> Fixes: 4180bf1b65 (KVM: X86: Implement "send IPI" hypercall)
> Reported-by: Wei Wu <ww9210@gmail.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Wei Wu <ww9210@gmail.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/lapic.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 3cd227f..09e3a12 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -576,6 +576,11 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
> rcu_read_lock();
> map = rcu_dereference(kvm->arch.apic_map);
>
> + if (unlikely(!map)) {
> + count = -EOPNOTSUPP;
> + goto out;
> + }
> +
> if (min > map->max_apic_id)
> goto out;
> /* Bits above cluster_size are masked in the caller. */
>

Queued, thanks.

Paolo

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