[PATCH] drm/xe/tracing: Fix a potential TP_printk UAF

[Lucas De Marchi]

On Mon, Dec 23, 2024 at 05:33:10PM +0100, Thomas Hellström wrote:
>On Mon, 2024-12-23 at 07:44 -0800, Matthew Brost wrote:
>> On Mon, Dec 23, 2024 at 02:42:50PM +0100, Thomas Hellström wrote:
>> > The commit
>> > afd2627f727b ("tracing: Check "%s" dereference via the field and
>> > not the TP_printk format")
>> > exposes potential UAFs in the xe_bo_move trace event.
>> >
>> > Fix those by avoiding dereferencing the
>> > xe_mem_type_to_name[] array at TP_printk time.
>> >
>> > Since some code refactoring has taken place, explicit backporting
>> > may
>> > be needed for kernels older than 6.10.
>> >
>> > Fixes: e46d3f813abd ("drm/xe/trace: Extract bo, vm, vma traces")
>> > Cc: Gustavo Sousa <gustavo.sousa at intel.com>
>> > Cc: Lucas De Marchi <lucas.demarchi at intel.com>
>> > Cc: Radhakrishna Sripada <radhakrishna.sripada at intel.com>
>> > Cc: Matt Roper <matthew.d.roper at intel.com>
>> > Cc: "Thomas Hellström" <thomas.hellstrom at linux.intel.com>
>> > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>> > Cc: intel-xe at lists.freedesktop.org
>> > Cc: <stable at vger.kernel.org> # v6.11+
>> > Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>> > ---
>> >  drivers/gpu/drm/xe/xe_trace_bo.h | 12 ++++++------
>> >  1 file changed, 6 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/xe/xe_trace_bo.h
>> > b/drivers/gpu/drm/xe/xe_trace_bo.h
>> > index 1762dd30ba6d..ea50fee50c7d 100644
>> > --- a/drivers/gpu/drm/xe/xe_trace_bo.h
>> > +++ b/drivers/gpu/drm/xe/xe_trace_bo.h
>> > @@ -60,8 +60,8 @@ TRACE_EVENT(xe_bo_move,
>> >  	    TP_STRUCT__entry(
>> >  		     __field(struct xe_bo *, bo)
>> >  		     __field(size_t, size)
>> > -		     __field(u32, new_placement)
>> > -		     __field(u32, old_placement)
>> > +		     __string(new_placement_name,
>> > xe_mem_type_to_name[new_placement])
>> > +		     __string(old_placement_name,
>> > xe_mem_type_to_name[old_placement])
>> >  		     __string(device_id, __dev_name_bo(bo))
>> >  		     __field(bool, move_lacks_source)
>> >  			),
>> > @@ -69,15 +69,15 @@ TRACE_EVENT(xe_bo_move,
>> >  	    TP_fast_assign(
>> >  		   __entry->bo      = bo;
>> >  		   __entry->size = bo->size;
>> > -		   __entry->new_placement = new_placement;
>> > -		   __entry->old_placement = old_placement;
>> > +		   __assign_str(new_placement_name);
>> > +		   __assign_str(old_placement_name);
>> >  		   __assign_str(device_id);
>> >  		   __entry->move_lacks_source = move_lacks_source;
>> >  		   ),
>> >  	    TP_printk("move_lacks_source:%s, migrate object %p
>> > [size %zu] from %s to %s device_id:%s",
>> >  		      __entry->move_lacks_source ? "yes" : "no",
>> > __entry->bo, __entry->size,
>> > -		      xe_mem_type_to_name[__entry->old_placement],
>> > -		      xe_mem_type_to_name[__entry->new_placement],
>> > __get_str(device_id))
>>
>> So is this the UAF? i.e., The Xe module unloads and
>> xe_mem_type_to_name
>> is gone?
>
>I would imagine that's the intention of the warning. However removing
>the xe_module seems to empty the trace buffer of xe_bo_move events.
>Whether there is a race in that process or whether the TP_printk check
>can't distinguish between module local addresses and other addresses is
>hard to tell. In any case, it looks like we need to comply with the
>warning here (I suspect CI refuses to run otherwise), and since it only
>appears to trigger on the xe module load on my system, it's unlikely
>that mentioned commit will be reverted.

it's actually a false positive from afd2627f727b. See explanation
by Steve at https://lore.kernel.org/all/20241230141329.5f698715@batman.local.home/
the fix later on

Lucas De Marchi


>
>
>>
>> I noticed that xe_mem_type_to_name is not static, it likely should
>> be.
>> Would that help here?
>
>No, doesn't help unfortunately.
>
>/Thomas
>
>
>
>>
>> Matt
>>
>> > +		      __get_str(old_placement_name),
>> > +		      __get_str(new_placement_name),
>> > __get_str(device_id))
>> >  );
>> >  
>> >  DECLARE_EVENT_CLASS(xe_vma,
>> > --
>> > 2.47.1
>> >
>