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    SubjectRe: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry
    Got it. I'll try again later.

    Best Regards,
    Zheng Wang

    Jani Nikula <jani.nikula@linux.intel.com> 于2022年9月19日周一 17:30写道:
    >
    > On Mon, 19 Sep 2022, Zheng Wang <1002992920@qq.com> wrote:
    > > From afe79848cb74cc8e45ab426d13fa2394c87e0422 Mon Sep 17 00:00:00 2001
    > > From: xmzyshypnc <1002992920@qq.com>
    > > 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@qq.com>
    >
    > 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

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