drm/xe: Drop HW fence pointer to HW fence ctx

The HW fence ctx objects are not ref counted rather tied to the life of
an LRC object. HW fences reference the HW fence ctx, HW fences can
outlive LRCs thus resulting in UAF. Drop the  HW fence pointer to HW
fence ctx rather just store what is needed directly in HW fence.

v2:
 - Fix typo in commit (Ashutosh)
 - Use snprintf (Ashutosh)

Fixes: dd08ebf6 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240815193522.16008-1-matthew.brost@intel.com

drivers/gpu/drm/xe/xe_hw_fence.c

@@ -148,20 +148,20 @@ static const char *xe_hw_fence_get_driver_name(struct dma_fence *dma_fence)
 {
 	struct xe_hw_fence *fence = to_xe_hw_fence(dma_fence);
 
-	return dev_name(gt_to_xe(fence->ctx->gt)->drm.dev);
+	return dev_name(fence->xe->drm.dev);
 }
 
 static const char *xe_hw_fence_get_timeline_name(struct dma_fence *dma_fence)
 {
 	struct xe_hw_fence *fence = to_xe_hw_fence(dma_fence);
 
-	return fence->ctx->name;
+	return fence->name;
 }
 
 static bool xe_hw_fence_signaled(struct dma_fence *dma_fence)
 {
 	struct xe_hw_fence *fence = to_xe_hw_fence(dma_fence);
-	struct xe_device *xe = gt_to_xe(fence->ctx->gt);
+	struct xe_device *xe = fence->xe;
 	u32 seqno = xe_map_rd(xe, &fence->seqno_map, 0, u32);
 
 	return dma_fence->error ||
@@ -253,7 +253,8 @@ void xe_hw_fence_init(struct dma_fence *fence, struct xe_hw_fence_ctx *ctx,
 	struct  xe_hw_fence *hw_fence =
 		container_of(fence, typeof(*hw_fence), dma);
 
-	hw_fence->ctx = ctx;
+	hw_fence->xe = gt_to_xe(ctx->gt);
+	snprintf(hw_fence->name, sizeof(hw_fence->name), "%s", ctx->name);
 	hw_fence->seqno_map = seqno_map;
 	INIT_LIST_HEAD(&hw_fence->irq_link);
 

drivers/gpu/drm/xe/xe_hw_fence_types.h

@@ -12,6 +12,7 @@
 #include <linux/list.h>
 #include <linux/spinlock.h>
 
+struct xe_device;
 struct xe_gt;
 
 /**
@@ -61,8 +62,10 @@ struct xe_hw_fence_ctx {
 struct xe_hw_fence {
 	/** @dma: base dma fence for hardware fence context */
 	struct dma_fence dma;
-	/** @ctx: hardware fence context */
-	struct xe_hw_fence_ctx *ctx;
+	/** @xe: Xe device for hw fence driver name */
+	struct xe_device *xe;
+	/** @name: name of hardware fence context */
+	char name[MAX_FENCE_NAME_LEN];
 	/** @seqno_map: I/O map for seqno */
 	struct iosys_map seqno_map;
 	/** @irq_link: Link in struct xe_hw_fence_irq.pending */

drivers/gpu/drm/xe/xe_trace.h

@@ -309,7 +309,7 @@ DECLARE_EVENT_CLASS(xe_hw_fence,
 		    TP_ARGS(fence),
 
 		    TP_STRUCT__entry(
-			     __string(dev, __dev_name_gt(fence->ctx->gt))
+			     __string(dev, __dev_name_xe(fence->xe))
 			     __field(u64, ctx)
 			     __field(u32, seqno)
 			     __field(struct xe_hw_fence *, fence)