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drm/meson: Fix return type of meson_encoder_cvbs_mode_valid()

Message ID 20221102155242.1927166-1-nathan@kernel.org
State New
Headers
Series drm/meson: Fix return type of meson_encoder_cvbs_mode_valid() |

Commit Message

Nathan Chancellor Nov. 2, 2022, 3:52 p.m. UTC 
  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/meson/meson_encoder_cvbs.c:211:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' with an expression of type 'int (struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
          .mode_valid = meson_encoder_cvbs_mode_valid,
                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  1 error generated.

->mode_valid() in 'struct drm_bridge_funcs' expects a return type of
'enum drm_mode_status', not 'int'. Adjust the return type of
meson_encoder_cvbs_mode_valid() to match the prototype's to resolve the
warning and CFI failure.

Link: https://github.com/ClangBuiltLinux/linux/issues/1750
Reported-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 drivers/gpu/drm/meson/meson_encoder_cvbs.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)


base-commit: 9abf2313adc1ca1b6180c508c25f22f9395cc780

Comments

Kees Cook Nov. 2, 2022, 7:06 p.m. UTC | #1 
On Wed, Nov 02, 2022 at 08:52:42AM -0700, Nathan Chancellor wrote:
> 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/meson/meson_encoder_cvbs.c:211:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' with an expression of type 'int (struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
>           .mode_valid = meson_encoder_cvbs_mode_valid,
>                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   1 error generated.
> 
> ->mode_valid() in 'struct drm_bridge_funcs' expects a return type of
> 'enum drm_mode_status', not 'int'. Adjust the return type of
> meson_encoder_cvbs_mode_valid() to match the prototype's to resolve the
> warning and CFI failure.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Reported-by: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>
Neil Armstrong Nov. 3, 2022, 8:41 a.m. UTC | #2 
Hi,

On Wed, 2 Nov 2022 08:52:42 -0700, Nathan Chancellor wrote:
> 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:
> 
> [...]

Thanks, Applied to https://anongit.freedesktop.org/git/drm/drm-misc.git (drm-misc-next)

[1/1] drm/meson: Fix return type of meson_encoder_cvbs_mode_valid()
      https://cgit.freedesktop.org/drm/drm-misc/commit/?id=6c4e4d35203301906afb53c6d1e1302d4c793c05
diff mbox series

Patch

diff --git a/drivers/gpu/drm/meson/meson_encoder_cvbs.c b/drivers/gpu/drm/meson/meson_encoder_cvbs.c
index 5675bc2a92cf..3f73b211fa8e 100644
--- a/drivers/gpu/drm/meson/meson_encoder_cvbs.c
+++ b/drivers/gpu/drm/meson/meson_encoder_cvbs.c
@@ -116,9 +116,10 @@  static int meson_encoder_cvbs_get_modes(struct drm_bridge *bridge,
 	return i;
 }
 
-static int meson_encoder_cvbs_mode_valid(struct drm_bridge *bridge,
-					const struct drm_display_info *display_info,
-					const struct drm_display_mode *mode)
+static enum drm_mode_status
+meson_encoder_cvbs_mode_valid(struct drm_bridge *bridge,
+			      const struct drm_display_info *display_info,
+			      const struct drm_display_mode *mode)
 {
 	if (meson_cvbs_get_mode(mode))
 		return MODE_OK;