From: Nathan Chancellor nathan@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@kernel.org Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20221102155623.3042869-1-nathan@kernel.org Signed-off-by: Sasha Levin sashal@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 4be5b5670599..10e33a89b74c 100644 --- a/drivers/gpu/drm/sti/sti_dvo.c +++ b/drivers/gpu/drm/sti/sti_dvo.c @@ -354,8 +354,9 @@ 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 cbceea7d4f87..1c36758660f5 100644 --- a/drivers/gpu/drm/sti/sti_hda.c +++ b/drivers/gpu/drm/sti/sti_hda.c @@ -606,8 +606,9 @@ 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 c450668883b5..28186bcc8139 100644 --- a/drivers/gpu/drm/sti/sti_hdmi.c +++ b/drivers/gpu/drm/sti/sti_hdmi.c @@ -906,8 +906,9 @@ 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;