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[94.189.140.132]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7e67f5c55a2sm866617085a.36.2025.08.06.12.51.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 Aug 2025 12:51:58 -0700 (PDT) Message-ID: Date: Wed, 6 Aug 2025 21:51:07 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/9] kasan: introduce ARCH_DEFER_KASAN and unify static key across modes To: Sabyrzhan Tasbolatov Cc: hca@linux.ibm.com, christophe.leroy@csgroup.eu, andreyknvl@gmail.com, agordeev@linux.ibm.com, akpm@linux-foundation.org, zhangqing@loongson.cn, chenhuacai@loongson.cn, trishalfonso@google.com, davidgow@google.com, glider@google.com, dvyukov@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-um@lists.infradead.org, linux-mm@kvack.org References: <20250805142622.560992-1-snovitoll@gmail.com> <20250805142622.560992-2-snovitoll@gmail.com> <5a73e633-a374-47f2-a1e1-680e24d9f260@gmail.com> Content-Language: en-US From: Andrey Ryabinin In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/6/25 4:15 PM, Sabyrzhan Tasbolatov wrote: > On Wed, Aug 6, 2025 at 6:35 PM Andrey Ryabinin wrote: >> >> >> >> On 8/5/25 4:26 PM, Sabyrzhan Tasbolatov wrote: >>> Introduce CONFIG_ARCH_DEFER_KASAN to identify architectures that need >>> to defer KASAN initialization until shadow memory is properly set up, >>> and unify the static key infrastructure across all KASAN modes. >>> >>> Some architectures (like PowerPC with radix MMU) need to set up their >>> shadow memory mappings before KASAN can be safely enabled, while others >>> (like s390, x86, arm) can enable KASAN much earlier or even from the >>> beginning. >>> >>> Historically, the runtime static key kasan_flag_enabled existed only for >>> CONFIG_KASAN_HW_TAGS mode. Generic and SW_TAGS modes either relied on >>> architecture-specific kasan_arch_is_ready() implementations or evaluated >>> KASAN checks unconditionally, leading to code duplication. >>> >>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049 >>> Signed-off-by: Sabyrzhan Tasbolatov >>> --- >>> Changes in v4: >>> - Fixed HW_TAGS static key functionality (was broken in v3) >> >> I don't think it fixed. Before you patch kasan_enabled() esentially >> worked like this: >> >> if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) >> return static_branch_likely(&kasan_flag_enabled); >> else >> return IS_ENABLED(CONFIG_KASAN); >> >> Now it's just IS_ENABLED(CONFIG_KASAN); > > In v4 it is: > > #if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS) > static __always_inline bool kasan_shadow_initialized(void) > { > return static_branch_likely(&kasan_flag_enabled); > } > #else > static __always_inline bool kasan_shadow_initialized(void) > { > return kasan_enabled(); // which is IS_ENABLED(CONFIG_KASAN); > } > #endif > > So for HW_TAGS, KASAN is enabled in kasan_init_hw_tags(). You are referring to kasan_shadow_initialized(), but I was talking about kasan_enabled() specifically. E.g. your patch changes behavior for kasan_init_slab_obj() which doesn't use kasan_shadow_initialized() (in the case of HW_TAGS=y && kasan_flag_enabled = false) : static __always_inline void * __must_check kasan_init_slab_obj( struct kmem_cache *cache, const void *object) { if (kasan_enabled()) return __kasan_init_slab_obj(cache, object); return (void *)object; } >>> +#if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS) >>> +/* >>> + * Global runtime flag for KASAN modes that need runtime control. >>> + * Used by ARCH_DEFER_KASAN architectures and HW_TAGS mode. >>> + */ >>> DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled); >>> >>> -static __always_inline bool kasan_enabled(void) >>> +/* >>> + * Runtime control for shadow memory initialization or HW_TAGS mode. >>> + * Uses static key for architectures that need deferred KASAN or HW_TAGS. >>> + */ >>> +static __always_inline bool kasan_shadow_initialized(void) >> >> Don't rename it, just leave as is - kasan_enabled(). >> It's better name, shorter and you don't need to convert call sites, so >> there is less chance of mistakes due to unchanged kasan_enabled() -> kasan_shadow_initialized(). > > I actually had the only check "kasan_enabled()" in v2, but went to > double check approach in v3 > after this comment: > https://lore.kernel.org/all/CA+fCnZcGyTECP15VMSPh+duLmxNe=ApHfOnbAY3NqtFHZvceZw@mail.gmail.com/ AFAIU the comment suggest that we need two checks/flags, one in kasan_enabled() which checks whether kasan was enabled via cmdline (currently only for HW_TAGS) and one in kasan_arch_is_ready()(or kasan_shadow_initialized()) which checks if arch initialized KASAN. And this not what v3/v4 does. v4 basically have one check, just under different name. Separate checks might be needed if we have code paths that need 'kasan_arch_is_ready() && !kasan_enabled()' and vise versa '!kasan_arch_is_ready() && kasan_enabled()'. >From the top of my head, I can't say if we have such cases. > > Ok, we will have the **only** check kasan_enabled() then in > kasan-enabled.h which > > #if defined(CONFIG_ARCH_DEFER_KASAN) || defined(CONFIG_KASAN_HW_TAGS) > static __always_inline bool kasan_enabled(void) > { > return static_branch_likely(&kasan_flag_enabled); > } > #else > static inline bool kasan_enabled(void) > { > return IS_ENABLED(CONFIG_KASAN); > } > > And will remove kasan_arch_is_ready (current kasan_shadow_initialized in v4). > > So it is the single place to check if KASAN is enabled for all arch > and internal KASAN code. > Same behavior is in the current mainline code but only for HW_TAGS. > > Is this correct? > Yep, that's what I meant. >> >> >>> { >>> return static_branch_likely(&kasan_flag_enabled); >>> } >>> >>> -static inline bool kasan_hw_tags_enabled(void) >>> +static inline void kasan_enable(void) >>> +{ >>> + static_branch_enable(&kasan_flag_enabled); >>> +} >>> +#else >>> +/* For architectures that can enable KASAN early, use compile-time check. */ >>> +static __always_inline bool kasan_shadow_initialized(void) >>> { >>> return kasan_enabled(); >>> } >>> >> >> ... >> >>> >>> void kasan_populate_early_vm_area_shadow(void *start, unsigned long size); >>> -int kasan_populate_vmalloc(unsigned long addr, unsigned long size); >>> -void kasan_release_vmalloc(unsigned long start, unsigned long end, >>> + >>> +int __kasan_populate_vmalloc(unsigned long addr, unsigned long size); >>> +static inline int kasan_populate_vmalloc(unsigned long addr, unsigned long size) >>> +{ >>> + if (!kasan_shadow_initialized()) >>> + return 0; >> >> >> What's the point of moving these checks to header? >> Leave it in C, it's easier to grep and navigate code this way. > > Andrey Konovalov had comments [1] to avoid checks in C > by moving them to headers under __wrappers. > > : 1. Avoid spraying kasan_arch_is_ready() throughout the KASAN > : implementation and move these checks into include/linux/kasan.h (and > : add __wrappers when required). > > [1] https://lore.kernel.org/all/CA+fCnZcGyTECP15VMSPh+duLmxNe=ApHfOnbAY3NqtFHZvceZw@mail.gmail.com/ > I think Andrey K. meant cases when we have multiple implementations of one function for each mode. In such case it makes sense to merge multiple kasan_arch_is_ready() checks into one in the header. But in case like with kasan_populate_vmalloc() we have only one implementation so I don't see any value in adding wrapper/moving to header. >> >> >>> + return __kasan_populate_vmalloc(addr, size); >>> +} >>> + >>> +void __kasan_release_vmalloc(unsigned long start, unsigned long end, >>> unsigned long free_region_start, >>> unsigned long free_region_end, >>> unsigned long flags); >>> +static inline void kasan_release_vmalloc(unsigned long start, >>> + unsigned long end, >>> + unsigned long free_region_start, >>> + unsigned long free_region_end, >>> + unsigned long flags) >>> +{ >>> + if (kasan_shadow_initialized()) >>> + __kasan_release_vmalloc(start, end, free_region_start, >>> + free_region_end, flags); >>> +} >>> >> >> ...> @@ -250,7 +259,7 @@ static inline void poison_slab_object(struct kmem_cache *cache, void *object, >>> bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object, >>> unsigned long ip) >>> { >>> - if (!kasan_arch_is_ready() || is_kfence_address(object)) >>> + if (is_kfence_address(object)) >>> return false; >>> return check_slab_allocation(cache, object, ip); >>> } >>> @@ -258,7 +267,7 @@ bool __kasan_slab_pre_free(struct kmem_cache *cache, void *object, >>> bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init, >>> bool still_accessible) >>> { >>> - if (!kasan_arch_is_ready() || is_kfence_address(object)) >>> + if (is_kfence_address(object)) >>> return false; >>> >>> poison_slab_object(cache, object, init, still_accessible); >>> @@ -282,9 +291,6 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init, >>> >>> static inline bool check_page_allocation(void *ptr, unsigned long ip) >>> { >>> - if (!kasan_arch_is_ready()) >>> - return false; >>> - >> >> >> Well, you can't do this yet, because no arch using ARCH_DEFER_KASAN yet, so this breaks >> bisectability. >> Leave it, and remove with separate patch only when there are no users left. > > Will do in v5 at the end of patch series. > >> >>> if (ptr != page_address(virt_to_head_page(ptr))) { >>> kasan_report_invalid_free(ptr, ip, KASAN_REPORT_INVALID_FREE); >>> return true; >>> @@ -511,7 +517,7 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip) >>> return true; >>> } >>> >>> - if (is_kfence_address(ptr) || !kasan_arch_is_ready()) >>> + if (is_kfence_address(ptr)) >>> return true; >>> >>> slab = folio_slab(folio); >> >>