On Thu, May 01, 2025 at 05:24:38PM -0700, Kees Cook wrote: > Casting through a "void *" isn't sufficient to convince the randstruct > GCC plugin that the result is intentional. Instead operate through an > explicit union to silence the warning: > > drivers/gpu/drm/ttm/ttm_backup.c: In function 'ttm_file_to_backup': > drivers/gpu/drm/ttm/ttm_backup.c:21:16: note: randstruct: casting between > randomized structure pointer types (ssa): 'struct ttm_backup' and 'struct > file' > 21 | return (void *)file; > | ^~~~~~~~~~~~ > > Suggested-by: Matthew Brost <[email protected]>
I forgot the policy if suggest-by but will add: Reviewed-by: Matthew Brost <[email protected]> Thomas was out today I suspect he will look at this tomorrow when he is back too. Matt > Fixes: e7b5d23e5d47 ("drm/ttm: Provide a shmem backup implementation") > Signed-off-by: Kees Cook <[email protected]> > --- > v2: use struct and container_of (matthew) > v1: https://lore.kernel.org/all/[email protected]/ > Cc: Thomas Hellström <[email protected]> > Cc: Christian Koenig <[email protected]> > Cc: Somalapuram Amaranath <[email protected]> > Cc: Matthew Brost <[email protected]> > Cc: Huang Rui <[email protected]> > Cc: Matthew Auld <[email protected]> > Cc: Maarten Lankhorst <[email protected]> > Cc: Maxime Ripard <[email protected]> > Cc: Thomas Zimmermann <[email protected]> > Cc: David Airlie <[email protected]> > Cc: Simona Vetter <[email protected]> > Cc: <[email protected]> > --- > drivers/gpu/drm/ttm/ttm_backup.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/ttm/ttm_backup.c > b/drivers/gpu/drm/ttm/ttm_backup.c > index 93c007f18855..60cff6c60db4 100644 > --- a/drivers/gpu/drm/ttm/ttm_backup.c > +++ b/drivers/gpu/drm/ttm/ttm_backup.c > @@ -9,16 +9,21 @@ > > /* > * Casting from randomized struct file * to struct ttm_backup * is fine since > - * struct ttm_backup is never defined nor dereferenced. > + * struct ttm_backup is never defined nor dereferenced. Use a single-member > + * struct to avoid cast warnings. > */ > +struct ttm_backup { > + struct file file; > +}; > + > static struct file *ttm_backup_to_file(struct ttm_backup *backup) > { > - return (void *)backup; > + return &backup->file; > } > > static struct ttm_backup *ttm_file_to_backup(struct file *file) > { > - return (void *)file; > + return container_of(file, struct ttm_backup, file); > } > > /* > -- > 2.34.1 >
