Re: [Xen-devel] [Qemu-devel] [PATCH] xen/pt: Set is_express to avoid out-of-bounds write

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Sat, 28 Oct 2017, Simon Gaiser wrote:
> The passed-through device might be an express device. In this case the
> old code allocated a too small emulated config space in
> pci_config_alloc() since pci_config_size() returned the size for a
> non-express device. This leads to an out-of-bound write in
> xen_pt_config_reg_init(), which sometimes results in crashes. So set
> is_express as already done for KVM in vfio-pci.
> 
> Shortened ASan report:
> 
> ==17512==ERROR: AddressSanitizer: heap-buffer-overflow on address 
> 0x611000041648 at pc 0x55e0fdac51ff bp 0x7ffe4af07410 sp 0x7ffe4af07408
> WRITE of size 2 at 0x611000041648 thread T0
>     #0 0x55e0fdac51fe in memcpy 
> /usr/include/x86_64-linux-gnu/bits/string3.h:53
>     #1 0x55e0fdac51fe in stw_he_p include/qemu/bswap.h:330
>     #2 0x55e0fdac51fe in stw_le_p include/qemu/bswap.h:379
>     #3 0x55e0fdac51fe in pci_set_word include/hw/pci/pci.h:490
>     #4 0x55e0fdac51fe in xen_pt_config_reg_init 
> hw/xen/xen_pt_config_init.c:1991
>     #5 0x55e0fdac51fe in xen_pt_config_init hw/xen/xen_pt_config_init.c:2067
>     #6 0x55e0fdabcf4d in xen_pt_realize hw/xen/xen_pt.c:830
>     #7 0x55e0fdf59666 in pci_qdev_realize hw/pci/pci.c:2034
>     #8 0x55e0fdda7d3d in device_set_realized hw/core/qdev.c:914
> [...]
> 
> 0x611000041648 is located 8 bytes to the right of 256-byte region 
> [0x611000041540,0x611000041640)
> allocated by thread T0 here:
>     #0 0x7ff596a94bb8 in __interceptor_calloc 
> (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xd9bb8)
>     #1 0x7ff57da66580 in g_malloc0 
> (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x50580)
>     #2 0x55e0fdda7d3d in device_set_realized hw/core/qdev.c:914
> [...]
> 
> Signed-off-by: Simon Gaiser <hw42@xxxxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> 
> I found this by debugging crashes and I'm not familiar with this code,
> so I'm not sure if this has no unintended side effects.
> 
>  hw/xen/xen_pt.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
> index b6d71bb52a..90ffd45e7d 100644
> --- a/hw/xen/xen_pt.c
> +++ b/hw/xen/xen_pt.c
> @@ -946,6 +946,7 @@ static void xen_pci_passthrough_class_init(ObjectClass 
> *klass, void *data)
>      k->exit = xen_pt_unregister_device;
>      k->config_read = xen_pt_pci_read_config;
>      k->config_write = xen_pt_pci_write_config;
> +    k->is_express = 1; /* We might be */
>      set_bit(DEVICE_CATEGORY_MISC, dc->categories);
>      dc->desc = "Assign an host PCI device with Xen";
>      dc->props = xen_pci_passthrough_properties;
> -- 
> 2.15.0.rc1
> 
> 

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