[PATCH v3] drm/i915/gvt: fix double free bug in split_2MB_gtt_entry

[Zheng Wang]

If intel_gvt_dma_map_guest_page failed, it will call
ppgtt_invalidate_spt, which will finally free the spt.
But the caller does not notice that, it will free spt again in error path.

Fix this by spliting invalidate and free in ppgtt_invalidate_spt.
Only free spt when in good case.

Reported-by: Zheng Wang <hackerzheng666@xxxxxxxxx>
Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
---
v3:
- correct spelling mistake and remove unused variable suggested by Greg

v2: https://lore.kernel.org/all/20221006165845.1735393-1-zyytlz.wz@xxxxxxx/

v1: https://lore.kernel.org/all/20220928033340.1063949-1-zyytlz.wz@xxxxxxx/
---
 drivers/gpu/drm/i915/gvt/gtt.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index ce0eb03709c3..865d33762e45 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -959,6 +959,7 @@ static inline int ppgtt_put_spt(struct intel_vgpu_ppgtt_spt *spt)
 	return atomic_dec_return(&spt->refcount);
 }
 
+static int ppgtt_invalidate_and_free_spt(struct intel_vgpu_ppgtt_spt *spt);
 static int ppgtt_invalidate_spt(struct intel_vgpu_ppgtt_spt *spt);
 
 static int ppgtt_invalidate_spt_by_shadow_entry(struct intel_vgpu *vgpu,
@@ -995,7 +996,7 @@ static int ppgtt_invalidate_spt_by_shadow_entry(struct intel_vgpu *vgpu,
 				ops->get_pfn(e));
 		return -ENXIO;
 	}
-	return ppgtt_invalidate_spt(s);
+	return ppgtt_invalidate_and_free_spt(s);
 }
 
 static inline void ppgtt_invalidate_pte(struct intel_vgpu_ppgtt_spt *spt,
@@ -1016,18 +1017,30 @@ static inline void ppgtt_invalidate_pte(struct intel_vgpu_ppgtt_spt *spt,
 	intel_gvt_dma_unmap_guest_page(vgpu, pfn << PAGE_SHIFT);
 }
 
-static int ppgtt_invalidate_spt(struct intel_vgpu_ppgtt_spt *spt)
+static int ppgtt_invalidate_and_free_spt(struct intel_vgpu_ppgtt_spt *spt)
 {
-	struct intel_vgpu *vgpu = spt->vgpu;
-	struct intel_gvt_gtt_entry e;
-	unsigned long index;
 	int ret;
 
 	trace_spt_change(spt->vgpu->id, "die", spt,
-			spt->guest_page.gfn, spt->shadow_page.type);
-
+		spt->guest_page.gfn, spt->shadow_page.type);
 	if (ppgtt_put_spt(spt) > 0)
 		return 0;
+	ret = ppgtt_invalidate_spt(spt);
+	if (!ret) {
+		trace_spt_change(spt->vgpu->id, "release", spt,
+			 spt->guest_page.gfn, spt->shadow_page.type);
+		ppgtt_free_spt(spt);
+	}
+
+	return ret;
+}
+
+static int ppgtt_invalidate_spt(struct intel_vgpu_ppgtt_spt *spt)
+{
+	struct intel_vgpu *vgpu = spt->vgpu;
+	struct intel_gvt_gtt_entry e;
+	unsigned long index;
+	int ret;
 
 	for_each_present_shadow_entry(spt, &e, index) {
 		switch (e.type) {
@@ -1059,9 +1072,6 @@ static int ppgtt_invalidate_spt(struct intel_vgpu_ppgtt_spt *spt)
 		}
 	}
 
-	trace_spt_change(spt->vgpu->id, "release", spt,
-			 spt->guest_page.gfn, spt->shadow_page.type);
-	ppgtt_free_spt(spt);
 	return 0;
 fail:
 	gvt_vgpu_err("fail: shadow page %p shadow entry 0x%llx type %d\n",
@@ -1393,7 +1403,7 @@ static int ppgtt_handle_guest_entry_removal(struct intel_vgpu_ppgtt_spt *spt,
 			ret = -ENXIO;
 			goto fail;
 		}
-		ret = ppgtt_invalidate_spt(s);
+		ret = ppgtt_invalidate_and_free_spt(s);
 		if (ret)
 			goto fail;
 	} else {
-- 
2.25.1