Re: [PATCH V5 17/18] amdkfd: process debug trap ioctl only on a primary context

[Felix Kuehling <felix.kuehling@amd.com>]

On 2025-10-17 04:42, Zhu Lingshan wrote:
> Set_debug_trap ioctl should work on a specific kfd_process
> even when multiple contexts feature is implemented.
>
> For consistency, this commit allow set_debug_trap ioctl only work on the
> primary kfd process of a user space program
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@amd.com>
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_chardev.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> index 73de2de8be0f..7c02e8473622 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> @@ -2964,6 +2964,12 @@ static int kfd_ioctl_set_debug_trap(struct file *filep, struct kfd_process *p, v
>   		target = kfd_lookup_process_by_pid(pid);
>   	}
>   
> +	if (target->context_id != KFD_CONTEXT_ID_PRIMARY) {
> +		pr_debug("Set debug trap ioctl not supported on non-primary kfd process\n");
> +		r = -EOPNOTSUPP;
> +		goto out;
> +	}
> +

This check should be after the IS_ERR_OR_NULL(target) check below. 
Otherwise you dereference a bogus pointer.

We should also check that the process calling the ioctl is a primary 
context (p->context_id == KFD_CONTEXT_ID_PRIMARY). You don't want to 
allow a guest process (using a secondary context) to debug another 
process running on the host, using any ptrace the privileges of the QEMU 
host process.

Regards,
   Felix


>   	if (IS_ERR_OR_NULL(target)) {
>   		pr_debug("Cannot find process PID %i to debug\n", args->pid);
>   		r = target ? PTR_ERR(target) : -ESRCH;