diff options
| author | Eugeni Dodonov <eugeni.dodonov@intel.com> | 2011-11-10 13:55:15 -0200 |
|---|---|---|
| committer | Rohan Somvanshi <rsomvanshi@nvidia.com> | 2012-01-11 09:22:29 -0800 |
| commit | 23cd227590341dc0573d6d07b162b965e9fc47c6 (patch) | |
| tree | c5391c261470948656f90c4112b4a2adb5c6466a /drivers/gpu/drm/i915/i915_dma.c | |
| parent | 21eb1b986d9eff984552538196282ee066f001c9 (diff) | |
drm/i915: prevent division by zero when asking for chipset power
commit 4ed0b577457eb6aeb7cdc7e7316576e63d15abb2 upstream.
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>
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Change-Id: Ic86534499300b66168ad29ac08ab1e1f987de909
Reviewed-on: http://git-master/r/74160
Reviewed-by: Varun Wadekar <vwadekar@nvidia.com>
Tested-by: Varun Wadekar <vwadekar@nvidia.com>
Diffstat (limited to 'drivers/gpu/drm/i915/i915_dma.c')
| -rw-r--r-- | drivers/gpu/drm/i915/i915_dma.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c index 8a3942c4f099..c72b590f7d81 100644 --- a/drivers/gpu/drm/i915/i915_dma.c +++ b/drivers/gpu/drm/i915/i915_dma.c @@ -1453,6 +1453,14 @@ 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); @@ -1483,6 +1491,8 @@ 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; } |