drm/i915: Fix out-of-bounds array access in bdw_load_gamma_lut

bdw_load_gamma_lut is writing beyond the array to the maximum value.
The intend of the function is to clamp values > 1 to 1, so write
the intended color to the max register.

This fixes the following KASAN warning:

[  197.020857] [IGT] kms_pipe_color: executing
[  197.063434] [IGT] kms_pipe_color: starting subtest ctm-0-25-pipe0
[  197.078989] ==================================================================
[  197.079127] BUG: KASAN: slab-out-of-bounds in bdw_load_gamma_lut.isra.2+0x3b9/0x570 [i915]
[  197.079188] Read of size 2 at addr ffff8800d38db150 by task kms_pipe_color/1839
[  197.079208] CPU: 2 PID: 1839 Comm: kms_pipe_color Tainted: G     U 4.13.0-rc1-patser+ #5211
[  197.079215] Hardware name: NUC5i7RYB, BIOS RYBDWi35.86A.0246.2015.0309.1355 03/09/2015
[  197.079220] Call Trace:
[  197.079230]  dump_stack+0x68/0x9e
[  197.079239]  print_address_description+0x6f/0x250
[  197.079251]  kasan_report+0x216/0x370
[  197.079374]  ? bdw_load_gamma_lut.isra.2+0x3b9/0x570 [i915]
[  197.079451]  ? gen8_write16+0x4e0/0x4e0 [i915]
[  197.079460]  __asan_report_load2_noabort+0x14/0x20
[  197.079535]  bdw_load_gamma_lut.isra.2+0x3b9/0x570 [i915]
[  197.079612]  broadwell_load_luts+0x1df/0x550 [i915]
[  197.079690]  intel_color_load_luts+0x7b/0x80 [i915]
[  197.079764]  intel_begin_crtc_commit+0x138/0x760 [i915]
[  197.079783]  drm_atomic_helper_commit_planes_on_crtc+0x1a3/0x820 [drm_kms_helper]
[  197.079859]  ? intel_pre_plane_update+0x571/0x580 [i915]
[  197.079937]  intel_update_crtc+0x238/0x330 [i915]
[  197.080016]  intel_update_crtcs+0x10f/0x210 [i915]
[  197.080092]  intel_atomic_commit_tail+0x1552/0x3340 [i915]
[  197.080101]  ? _raw_spin_unlock+0x3c/0x40
[  197.080110]  ? __queue_work+0xb40/0xbf0
[  197.080188]  ? skl_update_crtcs+0xc00/0xc00 [i915]
[  197.080195]  ? trace_hardirqs_on+0xd/0x10
[  197.080269]  ? intel_atomic_commit_ready+0x128/0x13c [i915]
[  197.080329]  ? __i915_sw_fence_complete+0x5b8/0x6d0 [i915]
[  197.080336]  ? debug_object_activate+0x39e/0x580
[  197.080397]  ? i915_sw_fence_await+0x30/0x30 [i915]
[  197.080409]  ? __might_sleep+0x15b/0x180
[  197.080483]  intel_atomic_commit+0x944/0xa70 [i915]
[  197.080490]  ? refcount_dec_and_test+0x11/0x20
[  197.080567]  ? intel_atomic_commit_tail+0x3340/0x3340 [i915]
[  197.080597]  ? drm_atomic_crtc_set_property+0x303/0x580 [drm]
[  197.080674]  ? intel_atomic_commit_tail+0x3340/0x3340 [i915]
[  197.080704]  drm_atomic_commit+0xd7/0xe0 [drm]
[  197.080722]  drm_atomic_helper_crtc_set_property+0xec/0x130 [drm_kms_helper]
[  197.080749]  drm_mode_crtc_set_obj_prop+0x7d/0xb0 [drm]
[  197.080775]  drm_mode_obj_set_property_ioctl+0x50b/0x5d0 [drm]
[  197.080783]  ? __might_fault+0x104/0x180
[  197.080809]  ? drm_mode_obj_find_prop_id+0x160/0x160 [drm]
[  197.080838]  ? drm_mode_obj_find_prop_id+0x160/0x160 [drm]
[  197.080861]  drm_ioctl_kernel+0x154/0x1a0 [drm]
[  197.080885]  drm_ioctl+0x624/0x8f0 [drm]
[  197.080910]  ? drm_mode_obj_find_prop_id+0x160/0x160 [drm]
[  197.080934]  ? drm_getunique+0x210/0x210 [drm]
[  197.080943]  ? __handle_mm_fault+0x1bd0/0x1ce0
[  197.080949]  ? lock_downgrade+0x610/0x610
[  197.080957]  ? __lru_cache_add+0x15a/0x180
[  197.080967]  do_vfs_ioctl+0xd92/0xe40
[  197.080975]  ? ioctl_preallocate+0x1b0/0x1b0
[  197.080982]  ? selinux_capable+0x20/0x20
[  197.080991]  ? __do_page_fault+0x7b7/0x9a0
[  197.080997]  ? lock_downgrade+0x5bb/0x610
[  197.081007]  ? security_file_ioctl+0x57/0x90
[  197.081016]  SyS_ioctl+0x4e/0x80
[  197.081024]  entry_SYSCALL_64_fastpath+0x18/0xad
[  197.081030] RIP: 0033:0x7f61f287a987
[  197.081035] RSP: 002b:00007fff7d44d188 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  197.081043] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f61f287a987
[  197.081048] RDX: 00007fff7d44d1c0 RSI: 00000000c01864ba RDI: 0000000000000003
[  197.081053] RBP: 00007f61f2b3eb00 R08: 0000000000000059 R09: 0000000000000000
[  197.081058] R10: 0000002ea5c4a290 R11: 0000000000000246 R12: 00007f61f2b3eb58
[  197.081063] R13: 0000000000001010 R14: 00007f61f2b3eb58 R15: 0000000000002702

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101659Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reported-by: Martin Peres <martin.peres@linux.intel.com>
Cc: Martin Peres <martin.peres@linux.intel.com>
Fixes: 82cf435b ("drm/i915: Implement color management on bdw/skl/bxt/kbl")
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Kiran S Kumar <kiran.s.kumar@intel.com>
Cc: Kausal Malladi <kausalmalladi@gmail.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v4.7+
Link: https://patchwork.freedesktop.org/patch/msgid/20170724091431.24251-1-maarten.lankhorst@linux.intel.comReviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

drivers/gpu/drm/i915/intel_color.c

@@ -441,6 +441,7 @@ static void bdw_load_gamma_lut(struct drm_crtc_state *state, u32 offset)
 		}
 
 		/* Program the max register to clamp values > 1.0. */
+		i = lut_size - 1;
 		I915_WRITE(PREC_PAL_GC_MAX(pipe, 0),
 			   drm_color_lut_extract(lut[i].red, 16));
 		I915_WRITE(PREC_PAL_GC_MAX(pipe, 1),