On Fri, Sep 22, 2023 at 10:53 AM Kees Cook <[email protected]> wrote:
>
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> As found with Coccinelle[1], add __counted_by for struct mem_cgroup_threshold_ary.
>
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
>
> Cc: Andrew Morton <[email protected]>
> Cc: Shakeel Butt <[email protected]>
> Cc: Roman Gushchin <[email protected]>
> Cc: Johannes Weiner <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: "Matthew Wilcox (Oracle)" <[email protected]>
> Signed-off-by: Kees Cook <[email protected]>
> ---
> include/linux/memcontrol.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 45d0c10e86cc..e0cfab58ab71 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -143,7 +143,7 @@ struct mem_cgroup_threshold_ary {
> /* Size of entries[] */
> unsigned int size;
> /* Array of thresholds */
> - struct mem_cgroup_threshold entries[];
> + struct mem_cgroup_threshold entries[] __counted_by(size);
Does 'size' here have to be a member of the same struct as entries? We
have nodeinfo[] in struct mem_cgroup whose size is nr_node_ids which
is global. Will __counted_by() work for that?
On Fri, Sep 22, 2023 at 11:25:56AM -0700, Shakeel Butt wrote:
> On Fri, Sep 22, 2023 at 10:53 AM Kees Cook <[email protected]> wrote:
> >
> > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > attribute. Flexible array members annotated with __counted_by can have
> > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > functions).
> >
> > As found with Coccinelle[1], add __counted_by for struct mem_cgroup_threshold_ary.
> >
> > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> >
> > Cc: Andrew Morton <[email protected]>
> > Cc: Shakeel Butt <[email protected]>
> > Cc: Roman Gushchin <[email protected]>
> > Cc: Johannes Weiner <[email protected]>
> > Cc: Michal Hocko <[email protected]>
> > Cc: "Matthew Wilcox (Oracle)" <[email protected]>
> > Signed-off-by: Kees Cook <[email protected]>
> > ---
> > include/linux/memcontrol.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 45d0c10e86cc..e0cfab58ab71 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -143,7 +143,7 @@ struct mem_cgroup_threshold_ary {
> > /* Size of entries[] */
> > unsigned int size;
> > /* Array of thresholds */
> > - struct mem_cgroup_threshold entries[];
> > + struct mem_cgroup_threshold entries[] __counted_by(size);
>
> Does 'size' here have to be a member of the same struct as entries? We
> have nodeinfo[] in struct mem_cgroup whose size is nr_node_ids which
> is global. Will __counted_by() work for that?
Not presently, no. This may come in future expansions of the feature.
We're also hoping to gain expressions for places where a size isn't a
native count, like for big endian, or a byte count that includes the
entire struct, etc. For now, though, the feature is narrowly scoped just
to get the common case landed.
-Kees
--
Kees Cook