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

[Dave Airlie <airlied@gmail.com>]

On Fri, 7 Oct 2022 at 11:38, Zheng Wang <zyytlz.wz@163.com> wrote:
>
> 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@gmail.com>
> Signed-off-by: Zheng Wang <zyytlz.wz@163.com>

Has this landed in a tree yet, since it's a possible CVE, might be
good to merge it somewhere.

Dave.

> ---
> v3:
> - correct spelling mistake and remove unused variable suggested by Greg
>
> v2: https://lore.kernel.org/all/20221006165845.1735393-1-zyytlz.wz@163.com/
>
> v1: https://lore.kernel.org/all/20220928033340.1063949-1-zyytlz.wz@163.com/
> ---
>  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
>