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

[Felix Kuehling]

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....@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;