[PATCH v2 2/2] drm/i915: Validate userspace-provided color management LUT's (v2)

[Matt Roper]

We currently program userspace-provided gamma and degamma LUT's into our
hardware without really checking to see whether they satisfy our
hardware's rules.  We should try to catch tables that are invalid for
our hardware early and reject the atomic transaction.

All of our platforms that accept a degamma LUT expect that the entries
in the LUT are always flat or increasing, never decreasing.  Also, our
GLK and ICL platforms only accept degamma tables with r=g=b entries; so
we should also add the relevant checks for that in anticipation of
degamma support landing for those platforms.

v2:
 - Use new API (single check function with bitmask of tests to apply)
 - Call helper for our gamma table as well (with no additional tests
   specified) so that the table size will be validated.

Cc: Uma Shankar <uma.shankar at intel.com>
Cc: Swati Sharma <swati2.sharma at intel.com>
Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
---
 drivers/gpu/drm/i915/intel_color.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_color.c b/drivers/gpu/drm/i915/intel_color.c
index 37fd9ddf762e..5ad4459a5f3c 100644
--- a/drivers/gpu/drm/i915/intel_color.c
+++ b/drivers/gpu/drm/i915/intel_color.c
@@ -609,10 +609,29 @@ int intel_color_check(struct intel_crtc_state *crtc_state)
 {
 	struct drm_i915_private *dev_priv = to_i915(crtc_state->base.crtc->dev);
 	size_t gamma_length, degamma_length;
+	uint32_t tests = DRM_COLOR_LUT_INCREASING;
 
 	degamma_length = INTEL_INFO(dev_priv)->color.degamma_lut_size;
 	gamma_length = INTEL_INFO(dev_priv)->color.gamma_lut_size;
 
+	/*
+	 * All of our platforms mandate that the degamma curve be
+	 * non-decreasing.  Additionally, GLK and gen11 only accept a single
+	 * value for red, green, and blue in the degamma table.  Make sure
+	 * userspace didn't try to pass us something we can't handle.
+	 *
+	 * We don't have any extra hardware constraints on the gamma table,
+	 * so we just test that it's a proper size multiple
+	 * (tablesize % entrysize == 0).
+	 */
+	if (IS_GEMINILAKE(dev_priv) || INTEL_GEN(dev_priv) >= 11)
+		tests |= DRM_COLOR_LUT_EQUAL_CHANNELS;
+
+	if (drm_color_lut_check(crtc_state->base.degamma_lut, tests) != 0)
+		return -EINVAL;
+	if (drm_color_lut_check(crtc_state->base.gamma_lut, 0) != 0)
+		return -EINVAL;
+
 	/*
 	 * We allow both degamma & gamma luts at the right size or
 	 * NULL.
-- 
2.14.4