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References: <tencent_ED24158E83CB9885E8BDD173EB5896B51906@qq.com> <87pmfrpv7q.fsf@intel.com>
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From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Mon, 19 Sep 2022 17:55:35 +0800
Message-ID: <CAJedcCxWAjsB-zcGn_epE=1d=LTeX-ndNunLqQJ842+ptjy=Bw@mail.gmail.com>
Subject: Re: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry
To:     Jani Nikula <jani.nikula@linux.intel.com>
Cc:     Zheng Wang <1002992920@qq.com>, gregkh@linuxfoundation.org,
        alex000young@gmail.com, security@kernel.org,
        tvrtko.ursulin@linux.intel.com, airlied@linux.ie,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
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Got it. I'll try again later.

Best Regards,
Zheng Wang

Jani Nikula <jani.nikula@linux.intel.com> =E4=BA=8E2022=E5=B9=B49=E6=9C=881=
9=E6=97=A5=E5=91=A8=E4=B8=80 17:30=E5=86=99=E9=81=93=EF=BC=9A
>
> 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_ent=
ry
> >
> > 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 *vg=
pu,
> >           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 =3D 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 =3D intel_gvt_dma_map_guest_page(vgpu, start_gfn + sub_in=
dex,
> >                              PAGE_SIZE, &dma_addr);
> >           if (ret) {
> > -            ppgtt_invalidate_spt(spt);
> > +            ppgtt_invalidate_spt(spt, 1);
> >               return ret;
> >           }
> >           sub_se.val64 =3D se->val64;
> > @@ -1393,7 +1395,7 @@ static int ppgtt_handle_guest_entry_removal(struc=
t
> > intel_vgpu_ppgtt_spt *spt,
> >               ret =3D -ENXIO;
> >               goto fail;
> >           }
> > -        ret =3D ppgtt_invalidate_spt(s);
> > +        ret =3D ppgtt_invalidate_spt(s, 0);
> >           if (ret)
> >               goto fail;
> >       } else {
>
> --
> Jani Nikula, Intel Open Source Graphics Center