Re: [PATCH V4 5/9] mshv: Import data structs around device passthru from hyperv headers

[Mukesh R <mrathor@linux.microsoft.com>]

On 7/17/26 19:30, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The memory layout of `union hv_device_domain_id` is inverted compared to the expected Hyper-V ABI, resulting in corrupted device domain IDs being passed to the hypervisor.
> --
> 
> --- Patch [5]: [PATCH V4 5/9] mshv: Import data structs around device passthru from hyperv headers ---
> commit 02ed2cd292e85f0b6e754b6a29df473f95394315
> Author: Mukesh R <mrathor@linux.microsoft.com>
> 
> mshv: Import data structs around device passthru from hyperv headers
> 
> This commit copies and imports definitions and declarations from Hyper-V
> public headers. These additions are related to creating domains in the
> hypervisor and attaching devices to them.
> 
>> diff --git a/include/hyperv/hvhdk_mini.h b/include/hyperv/hvhdk_mini.h
>> index b4cb2fa26e9bc..90497635c3cbd 100644
>> --- a/include/hyperv/hvhdk_mini.h
>> +++ b/include/hyperv/hvhdk_mini.h
> 
> [ ... ]
> 
>> +/* 3 domain types: stage 1, stage 2, and SOC */
>> +#define HV_DEVICE_DOMAIN_TYPE_S2  0 /* HV_DEVICE_DOMAIN_ID_TYPE_S2 */
>> +#define HV_DEVICE_DOMAIN_TYPE_S1  1 /* HV_DEVICE_DOMAIN_ID_TYPE_S1 */
>> +#define HV_DEVICE_DOMAIN_TYPE_SOC 2 /* HV_DEVICE_DOMAIN_ID_TYPE_SOC */
>> +
>> +/* ID for stage 2 default domain and NULL domain */
>> +#define HV_DEVICE_DOMAIN_ID_S2_DEFAULT 0
>> +#define HV_DEVICE_DOMAIN_ID_S2_NULL    0xFFFFFFFFULL
>> +
>> +union hv_device_domain_id {
>> +	u64 as_uint64;
>> +	struct {
>> +		u32 type : 4;
>> +		u32 reserved : 28;
>> +		u32 id;
>> +	};
>> +} __packed;
> 
> [Severity: High]
> Is the memory layout of union hv_device_domain_id inverted compared to the
> expected Hyper-V ABI?

No.

> The macro HV_DEVICE_DOMAIN_ID_S2_NULL is defined as 0xFFFFFFFFULL, which
> places 0xFFFFFFFF in the lower 32 bits and 0 in the upper 32 bits. Given
> that Stage 2 (S2) domains have a type of 0, this macro implies that the id
> should be in the lower 32 bits and the type should be in the upper 32 bits.

HV_DEVICE_DOMAIN_ID_S2_NULL is never assigned to any data struct of
type "union hv_device_domain_id".


> However, union hv_device_domain_id defines type as the first bitfield
> (occupying the lower 32 bits) and id as the second (occupying the upper 32
> bits).
> 
> Under this layout, casting 0xFFFFFFFFULL evaluates to type = 15 and id = 0,
> instead of the expected type = 0 and id = 0xFFFFFFFF. Could this cause
> malformed domain IDs to be sent to the hypervisor?
>