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Subject: Re: [PATCH] drm/i915/gvt/scheduler: fix potential NULL pointer
 dereference
To:     Chris Wilson <chris@chris-wilson.co.uk>,
        Zhenyu Wang <zhenyuw@linux.intel.com>,
        Zhi Wang <zhi.a.wang@intel.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        David Airlie <airlied@linux.ie>
Cc:     intel-gvt-dev@lists.freedesktop.org,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <20180319193053.GA7016@embeddedgus>
 <152149190651.3594.5036347331521892974@mail.alporthouse.com>
 <8f70ff7b-9575-006b-2384-88899f24fda6@embeddedor.com>
 <152149459549.3594.15219721825785440264@mail.alporthouse.com>
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Message-ID: <276cc037-d768-1baa-aea5-da69c8d8a1e2@embeddedor.com>
Date:   Mon, 19 Mar 2018 16:45:24 -0500
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On 03/19/2018 04:23 PM, Chris Wilson wrote:
> Quoting Gustavo A. R. Silva (2018-03-19 20:50:12)
>> Hi Chris,
>>
>> On 03/19/2018 03:38 PM, Chris Wilson wrote:
>>> Quoting Gustavo A. R. Silva (2018-03-19 19:30:53)
>>>> _workload_ is being dereferenced before it is null checked, hence
>>>> there is a potential null pointer dereference.
>>>>
>>>> Fix this by moving the pointer dereference after _workload_ has
>>>> been null checked.
>>>
>>> The checks are misleading and not required.
>>
>> All of them?
>>
>> if (!workload || !reg_state || workload->ring_id != RCS)
>>          return;
> 
> workload can not be NULL (dereference in caller), reg_state can not be
> NULL (by construct from kmap()).
> 
> It may be not an RCS ring through

I got it.

I'll send the following patch then:

--- a/drivers/gpu/drm/i915/gvt/scheduler.c
+++ b/drivers/gpu/drm/i915/gvt/scheduler.c
@@ -74,7 +74,7 @@ static void sr_oa_regs(struct intel_vgpu_workload 
*workload,
                 i915_mmio_reg_offset(EU_PERF_CNTL6),
         };

-       if (!workload || !reg_state || workload->ring_id != RCS)
+       if(workload->ring_id != RCS)
                 return;

         if (save) {


Thanks
--
Gustavo