[PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

[PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

The pointer workload is dereferenced before it is null checked, hence
there is a potential for a null pointer dereference on workload. Fix
this by only dereferencing workload after it is null checked.

Detected by CoverityScan, CID#1466017 ("Dereference before null check")

Fixes: fa3dd623e559 ("drm/i915/gvt: keep oa config in shadow ctx")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/gpu/drm/i915/gvt/scheduler.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/gvt/scheduler.c
index 068126404151..f3010e365a48 100644
--- a/drivers/gpu/drm/i915/gvt/scheduler.c
+++ b/drivers/gpu/drm/i915/gvt/scheduler.c
@@ -60,9 +60,9 @@ static void set_context_pdp_root_pointer(
 static void sr_oa_regs(struct intel_vgpu_workload *workload,
 		u32 *reg_state, bool save)
 {
-	struct drm_i915_private *dev_priv = workload->vgpu->gvt->dev_priv;
-	u32 ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
-	u32 ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
+	struct drm_i915_private *dev_priv;
+	u32 ctx_oactxctrl;
+	u32 ctx_flexeu0;
 	int i = 0;
 	u32 flex_mmio[] = {
 		i915_mmio_reg_offset(EU_PERF_CNTL0),
@@ -77,6 +77,10 @@ static void sr_oa_regs(struct intel_vgpu_workload *workload,
 	if (!workload || !reg_state || workload->ring_id != RCS)
 		return;
 
+	dev_priv = workload->vgpu->gvt->dev_priv;
+	ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
+	ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
+
 	if (save) {
 		workload->oactxctrl = reg_state[ctx_oactxctrl + 1];
 
-- 
2.15.1

Re: [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

[Joe Perches]

On Wed, 2018-03-21 at 19:06 +0000, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> The pointer workload is dereferenced before it is null checked, hence
> there is a potential for a null pointer dereference on workload. Fix
> this by only dereferencing workload after it is null checked.
> 
> Detected by CoverityScan, CID#1466017 ("Dereference before null check")

Maybe true, but is it possible for workload to be null?
Maybe the null test should be removed instead.

> Fixes: fa3dd623e559 ("drm/i915/gvt: keep oa config in shadow ctx")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/gpu/drm/i915/gvt/scheduler.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/gvt/scheduler.c
> index 068126404151..f3010e365a48 100644
> --- a/drivers/gpu/drm/i915/gvt/scheduler.c
> +++ b/drivers/gpu/drm/i915/gvt/scheduler.c
> @@ -60,9 +60,9 @@ static void set_context_pdp_root_pointer(
>  static void sr_oa_regs(struct intel_vgpu_workload *workload,
>  		u32 *reg_state, bool save)
>  {
> -	struct drm_i915_private *dev_priv = workload->vgpu->gvt->dev_priv;
> -	u32 ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
> -	u32 ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
> +	struct drm_i915_private *dev_priv;
> +	u32 ctx_oactxctrl;
> +	u32 ctx_flexeu0;
>  	int i = 0;
>  	u32 flex_mmio[] = {
>  		i915_mmio_reg_offset(EU_PERF_CNTL0),
> @@ -77,6 +77,10 @@ static void sr_oa_regs(struct intel_vgpu_workload *workload,
>  	if (!workload || !reg_state || workload->ring_id != RCS)
>  		return;
>  
> +	dev_priv = workload->vgpu->gvt->dev_priv;
> +	ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
> +	ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
> +
>  	if (save) {
>  		workload->oactxctrl = reg_state[ctx_oactxctrl + 1];
>  

Re: [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

[Colin Ian King]

On 21/03/18 19:09, Joe Perches wrote:
> On Wed, 2018-03-21 at 19:06 +0000, Colin King wrote:
>> From: Colin Ian King <colin.king@canonical.com>
>>
>> The pointer workload is dereferenced before it is null checked, hence
>> there is a potential for a null pointer dereference on workload. Fix
>> this by only dereferencing workload after it is null checked.
>>
>> Detected by CoverityScan, CID#1466017 ("Dereference before null check")
> 
> Maybe true, but is it possible for workload to be null?
> Maybe the null test should be removed instead.

>From what I understand from the static analysis, there may be a
potential for workload to be null, I couldn't rule it out so I went with
the more paranoid stance of keeping the null check in.

> 
>> Fixes: fa3dd623e559 ("drm/i915/gvt: keep oa config in shadow ctx")
>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>> ---
>>  drivers/gpu/drm/i915/gvt/scheduler.c | 10 +++++++---
>>  1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/gvt/scheduler.c
>> index 068126404151..f3010e365a48 100644
>> --- a/drivers/gpu/drm/i915/gvt/scheduler.c
>> +++ b/drivers/gpu/drm/i915/gvt/scheduler.c
>> @@ -60,9 +60,9 @@ static void set_context_pdp_root_pointer(
>>  static void sr_oa_regs(struct intel_vgpu_workload *workload,
>>  		u32 *reg_state, bool save)
>>  {
>> -	struct drm_i915_private *dev_priv = workload->vgpu->gvt->dev_priv;
>> -	u32 ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
>> -	u32 ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
>> +	struct drm_i915_private *dev_priv;
>> +	u32 ctx_oactxctrl;
>> +	u32 ctx_flexeu0;
>>  	int i = 0;
>>  	u32 flex_mmio[] = {
>>  		i915_mmio_reg_offset(EU_PERF_CNTL0),
>> @@ -77,6 +77,10 @@ static void sr_oa_regs(struct intel_vgpu_workload *workload,
>>  	if (!workload || !reg_state || workload->ring_id != RCS)
>>  		return;
>>  
>> +	dev_priv = workload->vgpu->gvt->dev_priv;
>> +	ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
>> +	ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
>> +
>>  	if (save) {
>>  		workload->oactxctrl = reg_state[ctx_oactxctrl + 1];
>>  

Re: [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

[Chris Wilson]

Quoting Colin Ian King (2018-03-21 19:18:28)
> On 21/03/18 19:09, Joe Perches wrote:
> > On Wed, 2018-03-21 at 19:06 +0000, Colin King wrote:
> >> From: Colin Ian King <colin.king@canonical.com>
> >>
> >> The pointer workload is dereferenced before it is null checked, hence
> >> there is a potential for a null pointer dereference on workload. Fix
> >> this by only dereferencing workload after it is null checked.
> >>
> >> Detected by CoverityScan, CID#1466017 ("Dereference before null check")
> > 
> > Maybe true, but is it possible for workload to be null?
> > Maybe the null test should be removed instead.
> 
> From what I understand from the static analysis, there may be a
> potential for workload to be null, I couldn't rule it out so I went with
> the more paranoid stance of keeping the null check in.

Not sr_oa_regs() problem if workload is NULL, that's the callers. I
reviewed the identical patch yesterday, and we ended up with removing
the NULL checks, just keeping the workload->id != RCS.
-Chris

Re: [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

[Colin Ian King]

On 21/03/18 19:23, Chris Wilson wrote:
> Quoting Colin Ian King (2018-03-21 19:18:28)
>> On 21/03/18 19:09, Joe Perches wrote:
>>> On Wed, 2018-03-21 at 19:06 +0000, Colin King wrote:
>>>> From: Colin Ian King <colin.king@canonical.com>
>>>>
>>>> The pointer workload is dereferenced before it is null checked, hence
>>>> there is a potential for a null pointer dereference on workload. Fix
>>>> this by only dereferencing workload after it is null checked.
>>>>
>>>> Detected by CoverityScan, CID#1466017 ("Dereference before null check")
>>>
>>> Maybe true, but is it possible for workload to be null?
>>> Maybe the null test should be removed instead.
>>
>> From what I understand from the static analysis, there may be a
>> potential for workload to be null, I couldn't rule it out so I went with
>> the more paranoid stance of keeping the null check in.
> 
> Not sr_oa_regs() problem if workload is NULL, that's the callers. I
> reviewed the identical patch yesterday, and we ended up with removing
> the NULL checks, just keeping the workload->id != RCS.
> -Chris
> 
Ah, OK, thanks for the clarification Chris.

Re: [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

[Joe Perches]

On Wed, 2018-03-21 at 19:18 +0000, Colin Ian King wrote:
> On 21/03/18 19:09, Joe Perches wrote:
> > On Wed, 2018-03-21 at 19:06 +0000, Colin King wrote:
> > > From: Colin Ian King <colin.king@canonical.com>
> > > 
> > > The pointer workload is dereferenced before it is null checked, hence
> > > there is a potential for a null pointer dereference on workload. Fix
> > > this by only dereferencing workload after it is null checked.
> > > 
> > > Detected by CoverityScan, CID#1466017 ("Dereference before null check")
> > 
> > Maybe true, but is it possible for workload to be null?
> > Maybe the null test should be removed instead.
> 
> From what I understand from the static analysis, there may be a
> potential for workload to be null, I couldn't rule it out so I went with
> the more paranoid stance of keeping the null check in.

workload cannot be null here.

Look at the uses of sr_oa_regs and see that
workload has already been dereferenced.

> > 
> > > Fixes: fa3dd623e559 ("drm/i915/gvt: keep oa config in shadow ctx")
> > > Signed-off-by: Colin Ian King <colin.king@canonical.com>
> > > ---
> > >  drivers/gpu/drm/i915/gvt/scheduler.c | 10 +++++++---
> > >  1 file changed, 7 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/gvt/scheduler.c
> > > index 068126404151..f3010e365a48 100644
> > > --- a/drivers/gpu/drm/i915/gvt/scheduler.c
> > > +++ b/drivers/gpu/drm/i915/gvt/scheduler.c
> > > @@ -60,9 +60,9 @@ static void set_context_pdp_root_pointer(
> > >  static void sr_oa_regs(struct intel_vgpu_workload *workload,
> > >  		u32 *reg_state, bool save)
> > >  {
> > > -	struct drm_i915_private *dev_priv = workload->vgpu->gvt->dev_priv;
> > > -	u32 ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
> > > -	u32 ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
> > > +	struct drm_i915_private *dev_priv;
> > > +	u32 ctx_oactxctrl;
> > > +	u32 ctx_flexeu0;
> > >  	int i = 0;
> > >  	u32 flex_mmio[] = {
> > >  		i915_mmio_reg_offset(EU_PERF_CNTL0),
> > > @@ -77,6 +77,10 @@ static void sr_oa_regs(struct intel_vgpu_workload *workload,
> > >  	if (!workload || !reg_state || workload->ring_id != RCS)
> > >  		return;
> > >  
> > > +	dev_priv = workload->vgpu->gvt->dev_priv;
> > > +	ctx_oactxctrl = dev_priv->perf.oa.ctx_oactxctrl_offset;
> > > +	ctx_flexeu0 = dev_priv->perf.oa.ctx_flexeu0_offset;
> > > +
> > >  	if (save) {
> > >  		workload->oactxctrl = reg_state[ctx_oactxctrl + 1];
> > >  
> 
>