Date:   Fri, 16 Sep 2022 14:39:21 +0800
From:   Zheng Hacker <hackerzheng666@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Zhenyu Wang <zhenyuw@...ux.intel.com>,
        "alex000young@...il.com" <alex000young@...il.com>,
        "security@...nel.org" <security@...nel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "tvrtko.ursulin@...ux.intel.com" <tvrtko.ursulin@...ux.intel.com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        xmzyshypnc <1002992920@...com>,
        "jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "rodrigo.vivi@...el.com" <rodrigo.vivi@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "zhi.a.wang@...el.com" <zhi.a.wang@...el.com>
Subject: Re: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry.

>From 8d95c1399e3ff345500a575e21254a73b0c89144 Mon Sep 17 00:00:00 2001
From: xmzyshypnc <1002992920@...com>
Date: Fri, 16 Sep 2022 14:37:48 +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@...com>
---
 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 9f14fded8c0c..31d2a8d56384 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 *sptm,
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) {
- ret = ppgtt_invalidate_spt(spt);
+ ret = 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

Zheng Hacker <hackerzheng666@...il.com> 于2022年9月8日周四 19:59写道：
>
> Hi Greg,
>
> I got it, Greg.
>
> Mid-Autumn Festival is coming and I will have a couple of days off.
> I'll see what I can do after holiday :)
>
> Regards,
>
> Zheng Wang
>
> 在 2022年9月8日星期四，Greg KH <gregkh@...uxfoundation.org> 写道：
>>
>> On Thu, Sep 08, 2022 at 05:09:40PM +0800, Zheng Hacker wrote:
>> > Hi Zhenyu,
>> >
>> > This issue has been open for a few days. Could you plz write a patch
>> > for that :) I'm not familiar with the logical code here.
>>
>> As this is only able to be hit in a theoretical system, it isn't that
>> high of a priority, if any priority at all.  Why not try to write a
>> patch for it yourself to help resolve the issue faster?
>>
>> thanks,
>>
>> greg k-h

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