Re: [PATCH rc v2] iommufd: Explicitize struct iommu_hwpt_pgfault padding

[Jason Gunthorpe]

On Sun, Jan 19, 2025 at 10:24:11PM -0800, Nicolin Chen wrote:
> --- a/drivers/iommu/iommufd/fault.c
> +++ b/drivers/iommu/iommufd/fault.c
> @@ -253,6 +253,7 @@ static void iommufd_compose_fault_message(struct iommu_fault *fault,
>  	hwpt_fault->pasid = fault->prm.pasid;
>  	hwpt_fault->grpid = fault->prm.grpid;
>  	hwpt_fault->perm = fault->prm.perm;
> +	hwpt_fault->__reserved = 0;
>  	hwpt_fault->addr = fault->prm.addr;
>  	hwpt_fault->length = 0;
>  	hwpt_fault->cookie = cookie;

Yikes, so it was leaking kernel stack memory through the padding too.

We should zero init the stack struct to be safe:

@@ -247,7 +247,7 @@ static ssize_t iommufd_fault_fops_read(struct file *filep, char __user *buf,
 {
        size_t fault_size = sizeof(struct iommu_hwpt_pgfault);
        struct iommufd_fault *fault = filep->private_data;
-       struct iommu_hwpt_pgfault data;
+       struct iommu_hwpt_pgfault data = {};
        struct iommufd_device *idev;
        struct iopf_group *group;
        struct iopf_fault *iopf;

I can fix it up if that is the only change

Jason