Re: [PATCH] drm/xe: Fix slab-out-of-bounds on PT update ops retry

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

On Thu, Apr 02, 2026 at 07:42:06PM -0700, Matthew Brost wrote:
> On Thu, Apr 02, 2026 at 11:15:39AM +0200, Thomas Hellström wrote:
> > xe_pt_update_ops_prepare() calls xe_pt_update_ops_init() at the start of
> > each invocation to reset per-attempt state, but current_op was not
> > included in that reset. When vm_bind_ioctl_ops_execute() retries due to
> > ww-mutex contention (drm_exec_retry_on_contention), ops_execute() calls
> 
> I'm falling to see retry path around vm_bind_ioctl_ops_execute related
> to drm_exec_retry_on_contention... Also by the time we get to
> vm_bind_ioctl_ops_execute we have all dma-resv, right?

s/vm_bind_ioctl_ops_execute/ops_execute here...

Matt

> 
> I believe the Kasan report but I just can't spot the bug - can you point
> out the retry path to me?
> 
> Matt
> 
> > xe_pt_update_ops_prepare() again. The second call walks the same op list
> > and fills ops[] starting from current_op, which still holds the value
> > from the first attempt. This indexes past the end of the ops array
> > allocated by xe_vma_ops_alloc(), whose size was computed for a single
> > pass.
> > 
> > KASAN reported:
> >   BUG: KASAN: slab-out-of-bounds in bind_op_prepare+0x89c/0xae0 [xe]
> >   Write of size 8 at addr ffff88812e72bae8 by task xe_evict/2848
> >   [...]
> >   bind_op_prepare+0x89c/0xae0 [xe]
> >   xe_pt_update_ops_prepare+0xbd0/0x1570 [xe]
> >   ops_execute+0x3ae/0x2030 [xe]
> >   vm_bind_ioctl_ops_execute+0x4d5/0xed0 [xe]
> > 
> > The write lands at ops[1].vma (offset 360 into the second element of a
> > one-element 384-byte allocation) because entries[] is exactly 360 bytes
> > and current_op was 1 at the start of the retried prepare pass.
> > 
> > Fix by resetting current_op to 0 in xe_pt_update_ops_init().
> > 
> > Fixes: e8babb280b5e ("drm/xe: Convert multiple bind ops into single job")
> > Cc: Matthew Brost <matthew.brost@intel.com>
> > Cc: Matthew Auld <matthew.auld@intel.com>
> > Cc: <stable@vger.kernel.org> # v6.12+
> > Assisted-by: GitHub Copilot:claude-sonnet-4.6
> > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > ---
> >  drivers/gpu/drm/xe/xe_pt.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
> > index 8e5f4f0dea3f..3607cd57fc4c 100644
> > --- a/drivers/gpu/drm/xe/xe_pt.c
> > +++ b/drivers/gpu/drm/xe/xe_pt.c
> > @@ -2291,6 +2291,7 @@ xe_pt_update_ops_init(struct xe_vm_pgtable_update_ops *pt_update_ops)
> >  	init_llist_head(&pt_update_ops->deferred);
> >  	pt_update_ops->start = ~0x0ull;
> >  	pt_update_ops->last = 0x0ull;
> > +	pt_update_ops->current_op = 0;
> >  	xe_page_reclaim_list_init(&pt_update_ops->prl);
> >  }
> >  
> > -- 
> > 2.53.0
> >