[Intel-gfx] [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry

[Zheng Wang]

There is a double-free security bug in split_2MB_gtt_entry.

Here is a calling chain :
ppgtt_populate_spt->ppgtt_populate_shadow_entry->split_2MB_gtt_entry.

If intel_gvt_dma_map_guest_page failed, it will call
ppgtt_invalidate_spt, which will finally call ppgtt_free_spt and
kfree(spt). But the caller does not notice that, and it will call
ppgtt_free_spt again in error path.

Fix this by only freeing spt in ppgtt_invalidate_spt in good case.

Reported-by: Zheng Wang <hackerzheng...@gmail.com> Zhuorao Yang 
<alex000yo...@gmail.com>

Signed-off-by: Zheng Wang <zyytlz...@163.com>
---
 drivers/gpu/drm/i915/gvt/gtt.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index ce0eb03709c3..550519f0acca 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -959,7 +959,7 @@ static inline int ppgtt_put_spt(struct intel_vgpu_ppgtt_spt 
*spt)
        return atomic_dec_return(&spt->refcount);
 }
 
-static int ppgtt_invalidate_spt(struct intel_vgpu_ppgtt_spt *spt);
+static int ppgtt_invalidate_spt(struct intel_vgpu_ppgtt_spt *spt, int 
is_error);
 
 static int ppgtt_invalidate_spt_by_shadow_entry(struct intel_vgpu *vgpu,
                struct intel_gvt_gtt_entry *e)
@@ -995,7 +995,7 @@ 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_spt(s, 0);
 }
 
 static inline void ppgtt_invalidate_pte(struct intel_vgpu_ppgtt_spt *spt,
@@ -1016,7 +1016,7 @@ 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_spt(struct intel_vgpu_ppgtt_spt *spt, int is_error)
 {
        struct intel_vgpu *vgpu = spt->vgpu;
        struct intel_gvt_gtt_entry e;
@@ -1059,9 +1059,11 @@ static int ppgtt_invalidate_spt(struct 
intel_vgpu_ppgtt_spt *spt)
                }
        }
 
-       trace_spt_change(spt->vgpu->id, "release", spt,
+       if (!is_error) {
+               trace_spt_change(spt->vgpu->id, "release", spt,
                         spt->guest_page.gfn, spt->shadow_page.type);
-       ppgtt_free_spt(spt);
+               ppgtt_free_spt(spt);
+       }
        return 0;
 fail:
        gvt_vgpu_err("fail: shadow page %p shadow entry 0x%llx type %d\n",
@@ -1215,7 +1217,7 @@ static int split_2MB_gtt_entry(struct intel_vgpu *vgpu,
                ret = intel_gvt_dma_map_guest_page(vgpu, start_gfn + sub_index,
                                                   PAGE_SIZE, &dma_addr);
                if (ret) {
-                       ppgtt_invalidate_spt(spt);
+                       ppgtt_invalidate_spt(spt, 1);
                        return ret;
                }
                sub_se.val64 = se->val64;
@@ -1393,7 +1395,7 @@ 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_spt(s, 0);
                if (ret)
                        goto fail;
        } else {
-- 
2.25.1