[PATCH 5.15 783/913] drm/dp: Fix off-by-one in register cache size

[Greg Kroah-Hartman]

From: Kees Cook <keescook@xxxxxxxxxxxx>

commit d4da1f27396fb1dde079447a3612f4f512caed07 upstream.

The pcon_dsc_dpcd array holds 13 registers (0x92 through 0x9E). Fix the
math to calculate the max size. Found from a -Warray-bounds build:

drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_pcon_dsc_bpp_incr':
drivers/gpu/drm/drm_dp_helper.c:3130:28: error: array subscript 12 is outside array bounds of 'const u8[12]' {aka 'const unsigned char[12]'} [-Werror=array-bounds]
 3130 |         buf = pcon_dsc_dpcd[DP_PCON_DSC_BPP_INCR - DP_PCON_DSC_ENCODER];
      |               ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/drm_dp_helper.c:3126:39: note: while referencing 'pcon_dsc_dpcd'
 3126 | int drm_dp_pcon_dsc_bpp_incr(const u8 pcon_dsc_dpcd[DP_PCON_DSC_ENCODER_CAP_SIZE])
      |                              ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Fixes: e2e16da398d9 ("drm/dp_helper: Add support for Configuring DSC for HDMI2.1 Pcon")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20211214001849.GA62559@embeddedor/
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220105173310.2420598-1-keescook@xxxxxxxxxxxx
Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20220225035610.2552144-2-keescook@xxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/drm/drm_dp_helper.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -455,7 +455,7 @@ struct drm_panel;
 # define DP_FEC_BIT_ERROR_COUNT_CAP	    (1 << 3)
 
 /* DP-HDMI2.1 PCON DSC ENCODER SUPPORT */
-#define DP_PCON_DSC_ENCODER_CAP_SIZE        0xC	/* 0x9E - 0x92 */
+#define DP_PCON_DSC_ENCODER_CAP_SIZE        0xD	/* 0x92 through 0x9E */
 #define DP_PCON_DSC_ENCODER                 0x092
 # define DP_PCON_DSC_ENCODER_SUPPORTED      (1 << 0)
 # define DP_PCON_DSC_PPS_ENC_OVERRIDE       (1 << 1)