On Wed, 16 Jun 2021 at 10:02, Daniel Axtens <dja@xxxxxxxxxx> wrote: > Allow architectures to define a kasan_arch_is_ready() hook that bails > out of any function that's about to touch the shadow unless the arch > says that it is ready for the memory to be accessed. This is fairly > uninvasive and should have a negligible performance penalty. > > This will only work in outline mode, so an arch must specify > ARCH_DISABLE_KASAN_INLINE if it requires this. > > Cc: Balbir Singh <bsingharora@xxxxxxxxx> > Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > Suggested-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx> > Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> but also check if an assertion that this is only used with KASAN_GENERIC might make sense (below). Depends on how much we want to make sure kasan_arch_is_ready() could be useful for other modes (which I don't think it makes sense). > -- > > I discuss the justfication for this later in the series. Also, > both previous RFCs for ppc64 - by 2 different people - have > needed this trick! See: > - https://lore.kernel.org/patchwork/patch/592820/ # ppc64 hash series > - https://patchwork.ozlabs.org/patch/795211/ # ppc radix series > --- > mm/kasan/common.c | 4 ++++ > mm/kasan/generic.c | 3 +++ > mm/kasan/kasan.h | 4 ++++ > mm/kasan/shadow.c | 8 ++++++++ > 4 files changed, 19 insertions(+) > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 10177cc26d06..0ad615f3801d 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -331,6 +331,10 @@ static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object, > u8 tag; > void *tagged_object; > > + /* Bail if the arch isn't ready */ > + if (!kasan_arch_is_ready()) > + return false; > + > tag = get_tag(object); > tagged_object = object; > object = kasan_reset_tag(object); > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c > index 53cbf28859b5..c3f5ba7a294a 100644 > --- a/mm/kasan/generic.c > +++ b/mm/kasan/generic.c > @@ -163,6 +163,9 @@ static __always_inline bool check_region_inline(unsigned long addr, > size_t size, bool write, > unsigned long ret_ip) > { > + if (!kasan_arch_is_ready()) > + return true; > + > if (unlikely(size == 0)) > return true; > > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > index 8f450bc28045..19323a3d5975 100644 > --- a/mm/kasan/kasan.h > +++ b/mm/kasan/kasan.h > @@ -449,6 +449,10 @@ static inline void kasan_poison_last_granule(const void *address, size_t size) { > > #endif /* CONFIG_KASAN_GENERIC */ > > +#ifndef kasan_arch_is_ready > +static inline bool kasan_arch_is_ready(void) { return true; } > +#endif > + I've been trying to think of a way to make it clear this is only for KASAN_GENERIC mode, and not the others. An arch can always define this function, but of course it might not be used. One way would be to add an '#ifndef CONFIG_KASAN_GENERIC' in the #else case and #error if it's not generic mode. I think trying to make this do anything useful for SW_TAGS or HW_TAGS modes does not make sense (at least right now). > /* > * Exported functions for interfaces called from assembly or from generated > * code. Declarations here to avoid warning about missing declarations. > diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c > index 082ee5b6d9a1..3c7f7efe6f68 100644 > --- a/mm/kasan/shadow.c > +++ b/mm/kasan/shadow.c > @@ -73,6 +73,10 @@ void kasan_poison(const void *addr, size_t size, u8 value, bool init) > { > void *shadow_start, *shadow_end; > > + /* Don't touch the shadow memory if arch isn't ready */ > + if (!kasan_arch_is_ready()) > + return; > + > /* > * Perform shadow offset calculation based on untagged address, as > * some of the callers (e.g. kasan_poison_object_data) pass tagged > @@ -99,6 +103,10 @@ EXPORT_SYMBOL(kasan_poison); > #ifdef CONFIG_KASAN_GENERIC > void kasan_poison_last_granule(const void *addr, size_t size) > { > + /* Don't touch the shadow memory if arch isn't ready */ > + if (!kasan_arch_is_ready()) > + return; > + > if (size & KASAN_GRANULE_MASK) { > u8 *shadow = (u8 *)kasan_mem_to_shadow(addr + size); > *shadow = size & KASAN_GRANULE_MASK; > -- > 2.30.2 > > -- > You received this message because you are subscribed to the Google Groups "kasan-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20210616080244.51236-3-dja%40axtens.net.
