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SubjectRe: [PATCH v14 2/4] kasan: allow architectures to provide an outline readiness check
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Le 17/06/2021 à 08:39, 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
> ARCH_DISABLE_KASAN_INLINE if it requires this.
>
> Cc: Balbir Singh <bsingharora@gmail.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Signed-off-by: Daniel Axtens <dja@axtens.net>
>
> --
>
> 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
>
> I haven't been able to exercise the arch hook error for !GENERIC as I
> don't have a particularly modern aarch64 toolchain or a lot of experience
> cross-compiling with clang. But it does fire for GENERIC + INLINE on x86.
> ---
> mm/kasan/common.c | 4 ++++
> mm/kasan/generic.c | 3 +++
> mm/kasan/kasan.h | 8 ++++++++
> mm/kasan/shadow.c | 8 ++++++++
> 4 files changed, 23 insertions(+)
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 8f450bc28045..b18abaf8c78e 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -449,6 +449,14 @@ 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; }
> +#else
> +#if !defined(CONFIG_KASAN_GENERIC) || !defined(CONFIG_KASAN_OUTLINE)
> +#error kasan_arch_is_ready only works in KASAN generic outline mode!
> +#endif
> +#endif

Would be cleaner and more readable as

+#ifndef kasan_arch_is_ready
+static inline bool kasan_arch_is_ready(void) { return true; }
+#elif !defined(CONFIG_KASAN_GENERIC) || !defined(CONFIG_KASAN_OUTLINE)
+#error kasan_arch_is_ready only works in KASAN generic outline mode!
+#endif

> +
> /*
> * 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;
>

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