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

[Jani Nikula]

On Mon, 19 Sep 2022, Zheng Wang <1002992920@xxxxxx> wrote:
>  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: xmzyshypnc <1002992920@xxxxxx>

Please use git send-email. The patch is whitespace broken and line
wrapped, making it unusable.

BR,
Jani.


> ---
>   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 {

-- 
Jani Nikula, Intel Open Source Graphics Center