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| author | Eugeni Dodonov <eugeni.dodonov@intel.com> | 2011-11-10 16:55:15 +0100 |
|---|---|---|
| committer | Keith Packard <keithp@keithp.com> | 2011-12-16 17:49:56 +0100 |
| commit | 4ed0b577457eb6aeb7cdc7e7316576e63d15abb2 (patch) | |
| tree | 9ecf2ddc9ff64ce9a10e3e2b8827a9e7e2b34f8f /drivers | |
| parent | drm/i915: add PCH info to i915_capabilities (diff) | |
| download | linux-4ed0b577457eb6aeb7cdc7e7316576e63d15abb2.tar.xz linux-4ed0b577457eb6aeb7cdc7e7316576e63d15abb2.zip | |
drm/i915: prevent division by zero when asking for chipset power
This prevents an in-kernel division by zero which happens when we are
asking for i915_chipset_val too quickly, or within a race condition
between the power monitoring thread and userspace accesses via debugfs.
The issue can be reproduced easily via the following command:
while ``; do cat /sys/kernel/debug/dri/0/i915_emon_status; done
This is particularly dangerous because it can be triggered by
a non-privileged user by just reading the debugfs entry.
This issue was also found independently by Konstantin Belousov
<kostikbel@gmail.com>, who proposed a similar patch.
Reported-by: Konstantin Belousov <kostikbel@gmail.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/gpu/drm/i915/i915_dma.c | 10 | ||||
| -rw-r--r-- | drivers/gpu/drm/i915/i915_drv.h | 1 |
2 files changed, 11 insertions, 0 deletions
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c index a9533c54c93c..a9ae374861e7 100644 --- a/drivers/gpu/drm/i915/i915_dma.c +++ b/drivers/gpu/drm/i915/i915_dma.c @@ -1454,6 +1454,14 @@ unsigned long i915_chipset_val(struct drm_i915_private *dev_priv) diff1 = now - dev_priv->last_time1; + /* Prevent division-by-zero if we are asking too fast. + * Also, we don't get interesting results if we are polling + * faster than once in 10ms, so just return the saved value + * in such cases. + */ + if (diff1 <= 10) + return dev_priv->chipset_power; + count1 = I915_READ(DMIEC); count2 = I915_READ(DDREC); count3 = I915_READ(CSIEC); @@ -1484,6 +1492,8 @@ unsigned long i915_chipset_val(struct drm_i915_private *dev_priv) dev_priv->last_count1 = total_count; dev_priv->last_time1 = now; + dev_priv->chipset_power = ret; + return ret; } diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index 8ba88cfc36de..39a72f642b33 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -713,6 +713,7 @@ typedef struct drm_i915_private { u64 last_count1; unsigned long last_time1; + unsigned long chipset_power; u64 last_count2; struct timespec last_time2; unsigned long gfx_power; |