[PATCH AUTOSEL 4.19 2/3] drm/sti: Fix return type of sti_{dvo, hda, hdmi}_connector_mode_valid()

[Sasha Levin]

From: Nathan Chancellor <nathan at kernel.org>

[ Upstream commit 0ad811cc08a937d875cbad0149c1bab17f84ba05 ]

With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
indirect call targets are validated against the expected function
pointer prototype to make sure the call target is valid to help mitigate
ROP attacks. If they are not identical, there is a failure at run time,
which manifests as either a kernel panic or thread getting killed. A
proposed warning in clang aims to catch these at compile time, which
reveals:

  drivers/gpu/drm/sti/sti_hda.c:637:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_connector *, struct drm_display_mode *)' with an expression of type 'int (struct drm_connector *, struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
          .mode_valid = sti_hda_connector_mode_valid,
                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  drivers/gpu/drm/sti/sti_dvo.c:376:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_connector *, struct drm_display_mode *)' with an expression of type 'int (struct drm_connector *, struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
          .mode_valid = sti_dvo_connector_mode_valid,
                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  drivers/gpu/drm/sti/sti_hdmi.c:1035:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_connector *, struct drm_display_mode *)' with an expression of type 'int (struct drm_connector *, struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
          .mode_valid = sti_hdmi_connector_mode_valid,
                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

->mode_valid() in 'struct drm_connector_helper_funcs' expects a return
type of 'enum drm_mode_status', not 'int'. Adjust the return type of
sti_{dvo,hda,hdmi}_connector_mode_valid() to match the prototype's to
resolve the warning and CFI failure.

Link: https://github.com/ClangBuiltLinux/linux/issues/1750
Signed-off-by: Nathan Chancellor <nathan at kernel.org>
Reviewed-by: Kees Cook <keescook at chromium.org>
Signed-off-by: Kees Cook <keescook at chromium.org>
Link: https://lore.kernel.org/r/20221102155623.3042869-1-nathan@kernel.org
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/gpu/drm/sti/sti_dvo.c  | 5 +++--
 drivers/gpu/drm/sti/sti_hda.c  | 5 +++--
 drivers/gpu/drm/sti/sti_hdmi.c | 5 +++--
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/sti/sti_dvo.c b/drivers/gpu/drm/sti/sti_dvo.c
index b08376b7611b..08d096822f24 100644
--- a/drivers/gpu/drm/sti/sti_dvo.c
+++ b/drivers/gpu/drm/sti/sti_dvo.c
@@ -346,8 +346,9 @@ static int sti_dvo_connector_get_modes(struct drm_connector *connector)
 
 #define CLK_TOLERANCE_HZ 50
 
-static int sti_dvo_connector_mode_valid(struct drm_connector *connector,
-					struct drm_display_mode *mode)
+static enum drm_mode_status
+sti_dvo_connector_mode_valid(struct drm_connector *connector,
+			     struct drm_display_mode *mode)
 {
 	int target = mode->clock * 1000;
 	int target_min = target - CLK_TOLERANCE_HZ;
diff --git a/drivers/gpu/drm/sti/sti_hda.c b/drivers/gpu/drm/sti/sti_hda.c
index 19b9b5ed1297..9974c19c04c4 100644
--- a/drivers/gpu/drm/sti/sti_hda.c
+++ b/drivers/gpu/drm/sti/sti_hda.c
@@ -596,8 +596,9 @@ static int sti_hda_connector_get_modes(struct drm_connector *connector)
 
 #define CLK_TOLERANCE_HZ 50
 
-static int sti_hda_connector_mode_valid(struct drm_connector *connector,
-					struct drm_display_mode *mode)
+static enum drm_mode_status
+sti_hda_connector_mode_valid(struct drm_connector *connector,
+			     struct drm_display_mode *mode)
 {
 	int target = mode->clock * 1000;
 	int target_min = target - CLK_TOLERANCE_HZ;
diff --git a/drivers/gpu/drm/sti/sti_hdmi.c b/drivers/gpu/drm/sti/sti_hdmi.c
index ccf718404a1c..b5199dd4b817 100644
--- a/drivers/gpu/drm/sti/sti_hdmi.c
+++ b/drivers/gpu/drm/sti/sti_hdmi.c
@@ -989,8 +989,9 @@ static int sti_hdmi_connector_get_modes(struct drm_connector *connector)
 
 #define CLK_TOLERANCE_HZ 50
 
-static int sti_hdmi_connector_mode_valid(struct drm_connector *connector,
-					struct drm_display_mode *mode)
+static enum drm_mode_status
+sti_hdmi_connector_mode_valid(struct drm_connector *connector,
+			      struct drm_display_mode *mode)
 {
 	int target = mode->clock * 1000;
 	int target_min = target - CLK_TOLERANCE_HZ;
-- 
2.35.1