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SubjectRe: [PATCH v9 2/6] kasan: allow architectures to provide an outline readiness check
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Le 01/12/2020 à 17:16, Daniel Axtens a écrit :
> 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
> HAVE_ARCH_NO_KASAN_INLINE if it requires this.
>
> Cc: Balbir Singh <bsingharora@gmail.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Did I signed that off one day ? I can't remember.

Please update my email address, and maybe change it to a Suggested-by: ? I think the first
Signed-off-by: has to be the author of the patch.

> Signed-off-by: Daniel Axtens <dja@axtens.net>
>
> --
>
> 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
> ---
> include/linux/kasan.h | 4 ++++
> mm/kasan/common.c | 10 ++++++++++
> mm/kasan/generic.c | 3 +++
> 3 files changed, 17 insertions(+)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 30d343b4a40a..3df66fdf6662 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -20,6 +20,10 @@ struct kunit_kasan_expectation {
> bool report_found;
> };
>
> +#ifndef kasan_arch_is_ready
> +static inline bool kasan_arch_is_ready(void) { return true; }
> +#endif
> +
> extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
> extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
> extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 950fd372a07e..ba7744d3e319 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -117,6 +117,9 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
> {
> void *shadow_start, *shadow_end;
>
> + 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
> @@ -134,6 +137,9 @@ void kasan_unpoison_shadow(const void *address, size_t size)
> {
> u8 tag = get_tag(address);
>
> + if (!kasan_arch_is_ready())
> + return;
> +
> /*
> * Perform shadow offset calculation based on untagged address, as
> * some of the callers (e.g. kasan_unpoison_object_data) pass tagged
> @@ -406,6 +412,10 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
> if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
> return false;
>
> + /* We can't read the shadow byte if the arch isn't ready */
> + if (!kasan_arch_is_ready())
> + return false;
> +
> shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
> if (shadow_invalid(tag, shadow_byte)) {
> kasan_report_invalid_free(tagged_object, ip);
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index 248264b9cb76..e87404026b2b 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -169,6 +169,9 @@ static __always_inline bool check_memory_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;
>
>

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