On Thu, Jul 5, 2018 at 6:37 AM, Michel Dänzer michel@daenzer.net wrote:

On 2018-07-04 07:27 PM, Kees Cook wrote:

...

As already done treewide, switch from open-coded multiplication to 2-factor allocation helper.

Signed-off-by: Kees Cook keescook@chromium.org

drivers/gpu/drm/amd/display/modules/color/color_gamma.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/modules/color/color_gamma.c b/drivers/gpu/drm/amd/display/modules/color/color_gamma.c index 98edaefa2b47..ee69c949bfbf 100644 --- a/drivers/gpu/drm/amd/display/modules/color/color_gamma.c +++ b/drivers/gpu/drm/amd/display/modules/color/color_gamma.c @@ -1723,8 +1723,8 @@ bool mod_color_calculate_curve(enum dc_transfer_func_predefined trans, kvfree(rgb_regamma); } else if (trans == TRANSFER_FUNCTION_HLG || trans == TRANSFER_FUNCTION_HLG12) {

•         rgb_regamma = kvzalloc(sizeof(*rgb_regamma) *
  

•                                (MAX_HW_POINTS + _EXTRA_POINTS),
  

•         rgb_regamma = kvcalloc(MAX_HW_POINTS + _EXTRA_POINTS,
  

•                                sizeof(*rgb_regamma),
                                 GFP_KERNEL);
          if (!rgb_regamma)
                  goto rgb_regamma_alloc_fail;
  

@@ -1802,8 +1802,8 @@ bool mod_color_calculate_degamma_curve(enum dc_transfer_func_predefined trans, kvfree(rgb_degamma); } else if (trans == TRANSFER_FUNCTION_HLG || trans == TRANSFER_FUNCTION_HLG12) {

•         rgb_degamma = kvzalloc(sizeof(*rgb_degamma) *
  

•                                (MAX_HW_POINTS + _EXTRA_POINTS),
  

•         rgb_degamma = kvcalloc(MAX_HW_POINTS + _EXTRA_POINTS,
  

•                                sizeof(*rgb_degamma),
                                 GFP_KERNEL);
          if (!rgb_degamma)
                  goto rgb_degamma_alloc_fail;
  
  

Since the values are constant, kvcalloc incurs the overflow checking overhead for no gain.

The way the macros are designed, they'll get entirely optimized away in that case: http://lkml.kernel.org/r/CAGXu5jLw9kMZRkzL_Q7JdyyprntHF6bdVSE_vjyzect3CenDng...

Using this patch means if the code ever changes away from constants, it'll still be safe. And static checkers won't yell about the open-coded multiplication here. So it's only up-sides. :)

-Kees