On Thu, 11 Aug 2022 at 09:26, Imran Khan <imran.f.khan@xxxxxxxxxx> wrote: > > By default kfence allocation can happen for any slab object, whose size > is up to PAGE_SIZE, as long as that allocation is the first allocation > after expiration of kfence sample interval. But in certain debugging > scenarios we may be interested in debugging corruptions involving > some specific slub objects like dentry or ext4_* etc. In such cases > limiting kfence for allocations involving only specific slub objects > will increase the probablity of catching the issue since kfence pool > will not be consumed by other slab objects. > > This patch introduces a sysfs interface '/sys/kernel/slab/<name>/skip_kfence' > to disable kfence for specific slabs. Having the interface work in this > way does not impact current/default behavior of kfence and allows us to > use kfence for specific slabs (when needed) as well. The decision to > skip/use kfence is taken depending on whether kmem_cache.flags has > (newly introduced) SLAB_SKIP_KFENCE flag set or not. > > Signed-off-by: Imran Khan <imran.f.khan@xxxxxxxxxx> > --- > > This RFC patch is implementing the sysfs work mentioned in [1]. Since the > approach taken in [1] was not proper, I am sending this RFC patch as a > separate change. This design is much simpler and looks good to me. Feel free to send as a non-RFC. > [1]: https://lore.kernel.org/lkml/20220727234241.1423357-1-imran.f.khan@xxxxxxxxxx/ > > include/linux/slab.h | 6 ++++++ > mm/kfence/core.c | 7 +++++++ > mm/slub.c | 27 +++++++++++++++++++++++++++ > 3 files changed, 40 insertions(+) > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 0fefdf528e0d..947d912fd08c 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -119,6 +119,12 @@ > */ > #define SLAB_NO_USER_FLAGS ((slab_flags_t __force)0x10000000U) > > +#ifdef CONFIG_KFENCE > +#define SLAB_SKIP_KFENCE ((slab_flags_t __force)0x20000000U) > +#else > +#define SLAB_SKIP_KFENCE 0 > +#endif > + > /* The following flags affect the page allocator grouping pages by mobility */ > /* Objects are reclaimable */ > #define SLAB_RECLAIM_ACCOUNT ((slab_flags_t __force)0x00020000U) > diff --git a/mm/kfence/core.c b/mm/kfence/core.c > index c252081b11df..8c08ae2101d7 100644 > --- a/mm/kfence/core.c > +++ b/mm/kfence/core.c > @@ -1003,6 +1003,13 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) > return NULL; > } > > + /* > + * Skip allocations for this slab, if KFENCE has been disabled for > + * this slab. > + */ > + if (s->flags & SLAB_SKIP_KFENCE) > + return NULL; > + > if (atomic_inc_return(&kfence_allocation_gate) > 1) > return NULL; > #ifdef CONFIG_KFENCE_STATIC_KEYS > diff --git a/mm/slub.c b/mm/slub.c > index 862dbd9af4f5..ee8b48327536 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5745,6 +5745,30 @@ STAT_ATTR(CPU_PARTIAL_NODE, cpu_partial_node); > STAT_ATTR(CPU_PARTIAL_DRAIN, cpu_partial_drain); > #endif /* CONFIG_SLUB_STATS */ > > +#ifdef CONFIG_KFENCE > +static ssize_t skip_kfence_show(struct kmem_cache *s, char *buf) > +{ > + return sysfs_emit(buf, "%d\n", !!(s->flags & SLAB_SKIP_KFENCE)); > +} > + > +static ssize_t skip_kfence_store(struct kmem_cache *s, > + const char *buf, size_t length) > +{ > + int ret = length; > + > + if (buf[0] == '0') > + s->flags &= ~SLAB_SKIP_KFENCE; > + else if (buf[0] == '1') > + s->flags |= SLAB_SKIP_KFENCE; > + else > + ret = -EINVAL; > + > + return ret; > +} > +SLAB_ATTR(skip_kfence); > + ^ unnecessary space? > +#endif > + > static struct attribute *slab_attrs[] = { > &slab_size_attr.attr, > &object_size_attr.attr, > @@ -5812,6 +5836,9 @@ static struct attribute *slab_attrs[] = { > &failslab_attr.attr, > #endif > &usersize_attr.attr, > +#ifdef CONFIG_KFENCE > + &skip_kfence_attr.attr, > +#endif > > NULL > }; > > base-commit: 40d43a7507e1547dd45cb02af2e40d897c591870 > -- > 2.30.2 >
