A malformed partial DTB specifying both '#address-cells = <0>' and
'#size-cells = <0>' causes '(address_cells * 2 + size_cells)' to
evaluate to 0. This sum is subsequently used as a divisor when
calculating the number of regions in the 'xen,reg' property inside
handle_passthrough_prop():

    len = fdt32_to_cpu(xen_reg->len) / ((address_cells * 2 + size_cells) *
                                        sizeof(uint32_t));

This leads to a division by zero exception in the Xen hypervisor during
boot, causing a hypervisor panic/crash.

Fix this by validating that both 'address_cells' and 'size_cells'
are within the valid range of [1, 2] at the read side in scan_pfdt_node()
immediately after they are parsed. Any invalid cell size combination is
safely rejected early with an error message and return -EINVAL.

Fixes: 9ce974c47588 ("xen/arm: assign devices to boot domains")
Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@epam.com>
---
Changes in v4:
- put the expressions in brackets
- improve the message as Andrew suggested
---
 xen/common/device-tree/dom0less-build.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/common/device-tree/dom0less-build.c b/xen/common/device-tree/dom0less-build.c
index eacfd93087..47465a3609 100644
--- a/xen/common/device-tree/dom0less-build.c
+++ b/xen/common/device-tree/dom0less-build.c
@@ -341,6 +341,13 @@ static int __init scan_pfdt_node(struct kernel_info *kinfo, const void *pfdt,
     size_cells = device_tree_get_u32(pfdt, nodeoff, "#size-cells",
                                      DT_ROOT_NODE_SIZE_CELLS_DEFAULT);
 
+    if ( (address_cells < 1) || (address_cells > 2) ||
+         (size_cells < 1) || (size_cells > 2) )
+    {
+        dprintk(XENLOG_ERR "Invalid address_cells %u or size_cells %u\n");
+        return -EINVAL;
+    }
+
     node_next = fdt_first_subnode(pfdt, nodeoff);
     while ( node_next > 0 )
     {
-- 
2.43.0

On 7/9/26 1:47 PM, Dmytro Prokopchuk1 wrote:
> A malformed partial DTB specifying both '#address-cells = <0>' and
> '#size-cells = <0>' causes '(address_cells * 2 + size_cells)' to
> evaluate to 0. This sum is subsequently used as a divisor when
> calculating the number of regions in the 'xen,reg' property inside
> handle_passthrough_prop():
> 
>      len = fdt32_to_cpu(xen_reg->len) / ((address_cells * 2 + size_cells) *
>                                          sizeof(uint32_t));
> 
> This leads to a division by zero exception in the Xen hypervisor during
> boot, causing a hypervisor panic/crash.
> 
> Fix this by validating that both 'address_cells' and 'size_cells'
> are within the valid range of [1, 2] at the read side in scan_pfdt_node()
> immediately after they are parsed. Any invalid cell size combination is
> safely rejected early with an error message and return -EINVAL.
> 
> Fixes: 9ce974c47588 ("xen/arm: assign devices to boot domains")
> Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@epam.com>
> ---
> Changes in v4:
> - put the expressions in brackets
> - improve the message as Andrew suggested
> ---
>   xen/common/device-tree/dom0less-build.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/xen/common/device-tree/dom0less-build.c b/xen/common/device-tree/dom0less-build.c
> index eacfd93087..47465a3609 100644
> --- a/xen/common/device-tree/dom0less-build.c
> +++ b/xen/common/device-tree/dom0less-build.c
> @@ -341,6 +341,13 @@ static int __init scan_pfdt_node(struct kernel_info *kinfo, const void *pfdt,
>       size_cells = device_tree_get_u32(pfdt, nodeoff, "#size-cells",
>                                        DT_ROOT_NODE_SIZE_CELLS_DEFAULT);
>   
> +    if ( (address_cells < 1) || (address_cells > 2) ||
> +         (size_cells < 1) || (size_cells > 2) )
> +    {
> +        dprintk(XENLOG_ERR "Invalid address_cells %u or size_cells %u\n");

I think you missed arguments here:

dprintk(XENLOG_ERR,
         "Invalid address_cells %u or size_cells %u\n",
         address_cells, size_cells);

Thanks.

~ Oleksii

On 7/9/26 14:57, Oleksii Kurochko wrote:
> 
> 
> On 7/9/26 1:47 PM, Dmytro Prokopchuk1 wrote:
>> A malformed partial DTB specifying both '#address-cells = <0>' and
>> '#size-cells = <0>' causes '(address_cells * 2 + size_cells)' to
>> evaluate to 0. This sum is subsequently used as a divisor when
>> calculating the number of regions in the 'xen,reg' property inside
>> handle_passthrough_prop():
>>
>>      len = fdt32_to_cpu(xen_reg->len) / ((address_cells * 2 + 
>> size_cells) *
>>                                          sizeof(uint32_t));
>>
>> This leads to a division by zero exception in the Xen hypervisor during
>> boot, causing a hypervisor panic/crash.
>>
>> Fix this by validating that both 'address_cells' and 'size_cells'
>> are within the valid range of [1, 2] at the read side in scan_pfdt_node()
>> immediately after they are parsed. Any invalid cell size combination is
>> safely rejected early with an error message and return -EINVAL.
>>
>> Fixes: 9ce974c47588 ("xen/arm: assign devices to boot domains")
>> Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@epam.com>
>> ---
>> Changes in v4:
>> - put the expressions in brackets
>> - improve the message as Andrew suggested
>> ---
>>   xen/common/device-tree/dom0less-build.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/xen/common/device-tree/dom0less-build.c b/xen/common/ 
>> device-tree/dom0less-build.c
>> index eacfd93087..47465a3609 100644
>> --- a/xen/common/device-tree/dom0less-build.c
>> +++ b/xen/common/device-tree/dom0less-build.c
>> @@ -341,6 +341,13 @@ static int __init scan_pfdt_node(struct 
>> kernel_info *kinfo, const void *pfdt,
>>       size_cells = device_tree_get_u32(pfdt, nodeoff, "#size-cells",
>>                                        DT_ROOT_NODE_SIZE_CELLS_DEFAULT);
>> +    if ( (address_cells < 1) || (address_cells > 2) ||
>> +         (size_cells < 1) || (size_cells > 2) )
>> +    {
>> +        dprintk(XENLOG_ERR "Invalid address_cells %u or size_cells 
>> %u\n");
> 
> I think you missed arguments here:
> 
> dprintk(XENLOG_ERR,
>          "Invalid address_cells %u or size_cells %u\n",
>          address_cells, size_cells);
> 
> Thanks.
> 
> ~ Oleksii

Sorry, my bad.
Thanks you, Oleksii.