Re: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry.

[Zheng Hacker <hackerzheng666@xxxxxxxxx>]

>From afe79848cb74cc8e45ab426d13fa2394c87e0422 Mon Sep 17 00:00:00 2001
From: xmzyshypnc <1002992920@xxxxxx>
Date: Fri, 16 Sep 2022 23:48:23 +0800
Subject: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry

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.

Signed-off-by: Zheng Wang <hackerzheng666@xxxxxxxxx>
---
 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