[Intel-gfx] [PATCH 2/4] drm/i915/perf: Whitelist OA report trigger registers

[Lionel Landwerlin]

On 24/07/2020 13:19, Chris Wilson wrote:
> Quoting Lionel Landwerlin (2020-07-24 11:07:18)
>> On 24/07/2020 12:26, Chris Wilson wrote:
>>> Quoting Umesh Nerlige Ramappa (2020-07-24 01:18:59)
>>>> diff --git a/drivers/gpu/drm/i915/gt/selftest_workarounds.c b/drivers/gpu/drm/i915/gt/selftest_workarounds.c
>>>> index febc9e6692ba..3b1d3dbcd477 100644
>>>> --- a/drivers/gpu/drm/i915/gt/selftest_workarounds.c
>>>> +++ b/drivers/gpu/drm/i915/gt/selftest_workarounds.c
>>>> @@ -934,6 +934,10 @@ static bool pardon_reg(struct drm_i915_private *i915, i915_reg_t reg)
>>>>           static const struct regmask pardon[] = {
>>>>                   { GEN9_CTX_PREEMPT_REG, INTEL_GEN_MASK(9, 9) },
>>>>                   { GEN8_L3SQCREG4, INTEL_GEN_MASK(9, 9) },
>>>> +               { OAREPORTTRIG2, INTEL_GEN_MASK(8, 11) },
>>>> +               { OAREPORTTRIG6, INTEL_GEN_MASK(8, 11) },
>>>> +               { GEN12_OAG_OAREPORTTRIG2, INTEL_GEN_MASK(12, 12) },
>>>> +               { GEN12_OAG_OAREPORTTRIG6, INTEL_GEN_MASK(12, 12) },
>>> Because we are not making the mistake of exposing more globals, and the
>>> pardon is a list of our past sins, not an excuse for more.
>> I'm afraid the HW design leave us no choice on Gen12 :(
> The question then is how much mischief can a client get up to if they
> subvert the OA of the privileged user. It's a privilege escalation hole,
> but is there anything dangerous behind it? Or is it just going to disturb
> the data being fed to the privileged client... (Which seems scary enough.)
> -Chris

The trigger registers will allow any other application to generate 
reports in the global OA buffer.

If you've built your OA report parsing correctly, this shouldn't be a 
problem because you'll filter on context ID prior to the reason of the 
report being recorded.

That's a downside of this patch, that's also a feature because you can 
use this to monitor particular chunks of work in a global timeline of OA 
reports for multiple applications.


-Lionel