Re: [PATCH] drm/simpledrm: Fix return type of simpledrm_simple_display_pipe_mode_valid()

[Sami Tolvanen]

On Mon, Jul 25, 2022 at 4:37 PM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
>
> When booting a kernel compiled with clang's CFI protection
> (CONFIG_CFI_CLANG), there is a CFI failure in
> drm_simple_kms_crtc_mode_valid() when trying to call
> simpledrm_simple_display_pipe_mode_valid() through ->mode_valid():
>
> [    0.322802] CFI failure (target: simpledrm_simple_display_pipe_mode_valid+0x0/0x8):
> ...
> [    0.324928] Call trace:
> [    0.324969]  __ubsan_handle_cfi_check_fail+0x58/0x60
> [    0.325053]  __cfi_check_fail+0x3c/0x44
> [    0.325120]  __cfi_slowpath_diag+0x178/0x200
> [    0.325192]  drm_simple_kms_crtc_mode_valid+0x58/0x80
> [    0.325279]  __drm_helper_update_and_validate+0x31c/0x464
> ...
>
> The ->mode_valid() member in 'struct drm_simple_display_pipe_funcs'
> expects a return type of 'enum drm_mode_status', not 'int'. Correct it
> to fix the CFI failure.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 11e8f5fd223b ("drm: Add simpledrm driver")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1647
> Reported-by: Tomasz Paweł Gajc <tpgxyz@xxxxxxxxx>
> Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/tiny/simpledrm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
> index 768242a78e2b..5422363690e7 100644
> --- a/drivers/gpu/drm/tiny/simpledrm.c
> +++ b/drivers/gpu/drm/tiny/simpledrm.c
> @@ -627,7 +627,7 @@ static const struct drm_connector_funcs simpledrm_connector_funcs = {
>         .atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
>  };
>
> -static int
> +static enum drm_mode_status
>  simpledrm_simple_display_pipe_mode_valid(struct drm_simple_display_pipe *pipe,
>                                     const struct drm_display_mode *mode)
>  {

Thanks for fixing this, Nathan! The patch looks correct to me.

Reviewed-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>

Sami