Re: [PATCH] KVM: x86: fix out-of-bounds accesses of rtc_eoi map

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/11/2016 21:15, Radim Krčmář wrote:
> KVM was using arrays of size KVM_MAX_VCPUS with vcpu_id, but ID can be
> bigger that the maximal number of VCPUs, resulting in out-of-bounds
> access.
> 
> Found by syzkaller:
> 
>   BUG: KASAN: slab-out-of-bounds in __apic_accept_irq+0xb33/0xb50 at addr [...]
>   Write of size 1 by task a.out/27101
>   CPU: 1 PID: 27101 Comm: a.out Not tainted 4.9.0-rc5+ #49
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>    [...]
>   Call Trace:
>    [...] __apic_accept_irq+0xb33/0xb50 arch/x86/kvm/lapic.c:905
>    [...] kvm_apic_set_irq+0x10e/0x180 arch/x86/kvm/lapic.c:495
>    [...] kvm_irq_delivery_to_apic+0x732/0xc10 arch/x86/kvm/irq_comm.c:86
>    [...] ioapic_service+0x41d/0x760 arch/x86/kvm/ioapic.c:360
>    [...] ioapic_set_irq+0x275/0x6c0 arch/x86/kvm/ioapic.c:222
>    [...] kvm_ioapic_inject_all arch/x86/kvm/ioapic.c:235
>    [...] kvm_set_ioapic+0x223/0x310 arch/x86/kvm/ioapic.c:670
>    [...] kvm_vm_ioctl_set_irqchip arch/x86/kvm/x86.c:3668
>    [...] kvm_arch_vm_ioctl+0x1a08/0x23c0 arch/x86/kvm/x86.c:3999
>    [...] kvm_vm_ioctl+0x1fa/0x1a70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3099
> 
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: stable@vger.kernel.org
> Fixes: af1bae5497b9 ("KVM: x86: bump KVM_MAX_VCPU_ID to 1023")
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Steve Rutherford <srutherford@google.com>
> ---
>  arch/x86/kvm/ioapic.c | 2 +-
>  arch/x86/kvm/ioapic.h | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
> index 1a22de70f7f7..6e219e5c07d2 100644
> --- a/arch/x86/kvm/ioapic.c
> +++ b/arch/x86/kvm/ioapic.c
> @@ -94,7 +94,7 @@ static unsigned long ioapic_read_indirect(struct kvm_ioapic *ioapic,
>  static void rtc_irq_eoi_tracking_reset(struct kvm_ioapic *ioapic)
>  {
>  	ioapic->rtc_status.pending_eoi = 0;
> -	bitmap_zero(ioapic->rtc_status.dest_map.map, KVM_MAX_VCPUS);
> +	bitmap_zero(ioapic->rtc_status.dest_map.map, KVM_MAX_VCPU_ID);
>  }
>  
>  static void kvm_rtc_eoi_tracking_restore_all(struct kvm_ioapic *ioapic);
> diff --git a/arch/x86/kvm/ioapic.h b/arch/x86/kvm/ioapic.h
> index 7d2692a49657..1cc6e54436db 100644
> --- a/arch/x86/kvm/ioapic.h
> +++ b/arch/x86/kvm/ioapic.h
> @@ -42,13 +42,13 @@ struct kvm_vcpu;
>  
>  struct dest_map {
>  	/* vcpu bitmap where IRQ has been sent */
> -	DECLARE_BITMAP(map, KVM_MAX_VCPUS);
> +	DECLARE_BITMAP(map, KVM_MAX_VCPU_ID);
>  
>  	/*
>  	 * Vector sent to a given vcpu, only valid when
>  	 * the vcpu's bit in map is set
>  	 */
> -	u8 vectors[KVM_MAX_VCPUS];
> +	u8 vectors[KVM_MAX_VCPU_ID];
>  };
>  
>  
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Prasad, this needs a CVE.

Paolo