Re: [PATCH] ARM/vgic: Fix out-of-bounds accesses in vgic_mmio_write_sgir()

[Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>]

Hi Andrew,

Andrew Cooper <andrew.cooper3@xxxxxxxxxx> writes:

> The switch() statement is over bits 24:25 (unshifted) of the guest provided
> value.  This makes case 0x3: dead, and not an implementation of the 4th
> possible state.
>
> A guest which writes (3<<24)|(ff<<16) to this register will skip the early
> exit, then enter bitmap_for_each() with targets not bound by nr_vcpus.
>
> If the guest has fewer than 8 vCPUs, bitmap_for_each() will read off the end
> of d->vcpu[] and use the resulting vcpu pointer to ultimately derive irq, and
> perform an out-of-bounds write.
>
> Fix this by changing case 0x3 to default.
>
> Fixes: 08c688ca6422 ("ARM: new VGIC: Add SGIR register handler")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>

> ---
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
> CC: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> CC: Michal Orzel <michal.orzel@xxxxxxx>
>
> This vgic driver is explicity not security supported, hence no XSA.
> ---
>  xen/arch/arm/vgic/vgic-mmio-v2.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/vgic/vgic-mmio-v2.c 
> b/xen/arch/arm/vgic/vgic-mmio-v2.c
> index 670b335db2c3..7d1391ac9b48 100644
> --- a/xen/arch/arm/vgic/vgic-mmio-v2.c
> +++ b/xen/arch/arm/vgic/vgic-mmio-v2.c
> @@ -104,7 +104,8 @@ static void vgic_mmio_write_sgir(struct vcpu *source_vcpu,
>      case GICD_SGI_TARGET_SELF:                    /* this very vCPU only */
>          targets = (1U << source_vcpu->vcpu_id);
>          break;
> -    case 0x3:                                     /* reserved */
> +
> +    default:
>          return;
>      }

-- 
WBR, Volodymyr