Re: [PATCH v2 2/3] drm/xe: Validate user fence during creation

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Mar 01, 2024 at 07:55:40AM +0100, Thomas Hellström wrote:
> On Thu, 2024-02-29 at 19:55 -0800, Matthew Brost wrote:
> > Fail invalidate addresses during user fence creation.
> > 
> > Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel
> > GPUs")
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > ---
> >  drivers/gpu/drm/xe/xe_sync.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_sync.c
> > b/drivers/gpu/drm/xe/xe_sync.c
> > index c836a5f3a1ea..c20e1f9ad267 100644
> > --- a/drivers/gpu/drm/xe/xe_sync.c
> > +++ b/drivers/gpu/drm/xe/xe_sync.c
> > @@ -53,14 +53,18 @@ static struct xe_user_fence
> > *user_fence_create(struct xe_device *xe, u64 addr,
> >  					       u64 value)
> >  {
> >  	struct xe_user_fence *ufence;
> > +	u64 __user *ptr = u64_to_user_ptr(addr);
> > +
> > +	if (!access_ok(ptr, sizeof(ptr)))
> > +		return ERR_PTR(-EFAULT);
> 
> I think we also need to enforce u64 alignment. Otherwise, particularly
> on 32-bit user-space the user fence memory could cross a page-border? 
> 

We already do this in xe_sync_entry_parse:

221                 if (XE_IOCTL_DBG(xe, sync_in.addr & 0x7))
222                         return -EINVAL;

Matt

> >  
> >  	ufence = kmalloc(sizeof(*ufence), GFP_KERNEL);
> >  	if (!ufence)
> > -		return NULL;
> > +		return ERR_PTR(-ENOMEM);
> >  
> >  	ufence->xe = xe;
> >  	kref_init(&ufence->refcount);
> > -	ufence->addr = u64_to_user_ptr(addr);
> > +	ufence->addr = ptr;
> >  	ufence->value = value;
> >  	ufence->mm = current->mm;
> >  	mmgrab(ufence->mm);
> > @@ -183,8 +187,8 @@ int xe_sync_entry_parse(struct xe_device *xe,
> > struct xe_file *xef,
> >  		} else {
> >  			sync->ufence = user_fence_create(xe,
> > sync_in.addr,
> >  							
> > sync_in.timeline_value);
> > -			if (XE_IOCTL_DBG(xe, !sync->ufence))
> > -				return -ENOMEM;
> > +			if (XE_IOCTL_DBG(xe, IS_ERR(sync->ufence)))
> > +				return PTR_ERR(sync->ufence);
> >  		}
> >  
> >  		break;
>