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[94.189.142.142]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-612c8f543ddsm5962670a12.30.2025.07.21.16.00.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Jul 2025 16:00:01 -0700 (PDT) Message-ID: <8f93322a-84c1-402b-b8d4-9c66a2b07b0b@gmail.com> Date: Tue, 22 Jul 2025 00:59:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 02/12] kasan: unify static kasan_flag_enabled across modes To: Sabyrzhan Tasbolatov , hca@linux.ibm.com, christophe.leroy@csgroup.eu, andreyknvl@gmail.com, agordeev@linux.ibm.com, akpm@linux-foundation.org Cc: 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: <20250717142732.292822-1-snovitoll@gmail.com> <20250717142732.292822-3-snovitoll@gmail.com> Content-Language: en-US From: Andrey Ryabinin In-Reply-To: <20250717142732.292822-3-snovitoll@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250721_160004_489513_BF15CCFD X-CRM114-Status: GOOD ( 29.31 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On 7/17/25 4:27 PM, Sabyrzhan Tasbolatov wrote: > 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. > > This patch implements two-level approach: > > 1. kasan_enabled() - controls if KASAN is enabled at all (compile-time) > 2. kasan_shadow_initialized() - tracks shadow memory > initialization (runtime) > > For architectures that select ARCH_DEFER_KASAN: kasan_shadow_initialized() > uses a static key that gets enabled when shadow memory is ready. > > For architectures that don't: kasan_shadow_initialized() returns > IS_ENABLED(CONFIG_KASAN) since shadow is ready from the start. > > This provides: > - Consistent interface across all KASAN modes > - Runtime control only where actually needed > - Compile-time constants for optimal performance where possible > - Clear separation between "KASAN configured" vs "shadow ready" > > Also adds kasan_init_generic() function that enables the shadow flag and > handles initialization for Generic mode, and updates SW_TAGS and HW_TAGS > to use the unified kasan_shadow_enable() function. > > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049 > Signed-off-by: Sabyrzhan Tasbolatov > --- > Changes in v3: > - Only architectures that need deferred KASAN get runtime overhead > - Added kasan_shadow_initialized() for shadow memory readiness tracking > - kasan_enabled() now provides compile-time check for KASAN configuration > --- > include/linux/kasan-enabled.h | 34 ++++++++++++++++++++++++++-------- > include/linux/kasan.h | 6 ++++++ > mm/kasan/common.c | 9 +++++++++ > mm/kasan/generic.c | 11 +++++++++++ > mm/kasan/hw_tags.c | 9 +-------- > mm/kasan/sw_tags.c | 2 ++ > 6 files changed, 55 insertions(+), 16 deletions(-) > > diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h > index 6f612d69ea0..fa99dc58f95 100644 > --- a/include/linux/kasan-enabled.h > +++ b/include/linux/kasan-enabled.h > @@ -4,32 +4,50 @@ > > #include > > -#ifdef CONFIG_KASAN_HW_TAGS > +/* Controls whether KASAN is enabled at all (compile-time check). */ > +static __always_inline bool kasan_enabled(void) > +{ > + return IS_ENABLED(CONFIG_KASAN); > +} > > +#ifdef CONFIG_ARCH_DEFER_KASAN > +/* > + * Global runtime flag for architectures that need deferred KASAN. > + * Switched to 'true' by the appropriate kasan_init_*() > + * once KASAN is fully initialized. > + */ > DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled); > > -static __always_inline bool kasan_enabled(void) > +static __always_inline bool kasan_shadow_initialized(void) > { > 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(); > } > > -#else /* CONFIG_KASAN_HW_TAGS */ > +/* No-op for architectures that don't need deferred KASAN. */ > +static inline void kasan_enable(void) {} > +#endif /* CONFIG_ARCH_DEFER_KASAN */ > > -static inline bool kasan_enabled(void) > +#ifdef CONFIG_KASAN_HW_TAGS > +static inline bool kasan_hw_tags_enabled(void) > { > - return IS_ENABLED(CONFIG_KASAN); > + return kasan_enabled(); > } > - > +#else > static inline bool kasan_hw_tags_enabled(void) > { > return false; > } > - > #endif /* CONFIG_KASAN_HW_TAGS */ > > #endif /* LINUX_KASAN_ENABLED_H */ > diff --git a/include/linux/kasan.h b/include/linux/kasan.h > index 890011071f2..51a8293d1af 100644 > --- a/include/linux/kasan.h > +++ b/include/linux/kasan.h > @@ -543,6 +543,12 @@ void kasan_report_async(void); > > #endif /* CONFIG_KASAN_HW_TAGS */ > > +#ifdef CONFIG_KASAN_GENERIC > +void __init kasan_init_generic(void); > +#else > +static inline void kasan_init_generic(void) { } > +#endif > + > #ifdef CONFIG_KASAN_SW_TAGS > void __init kasan_init_sw_tags(void); > #else > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index ed4873e18c7..c3a6446404d 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -32,6 +32,15 @@ > #include "kasan.h" > #include "../slab.h" > > +#ifdef CONFIG_ARCH_DEFER_KASAN > +/* > + * Definition of the unified static key declared in kasan-enabled.h. > + * This provides consistent runtime enable/disable across KASAN modes. > + */ > +DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled); > +EXPORT_SYMBOL(kasan_flag_enabled); > +#endif > + > struct slab *kasan_addr_to_slab(const void *addr) > { > if (virt_addr_valid(addr)) > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c > index d54e89f8c3e..03b6d322ff6 100644 > --- a/mm/kasan/generic.c > +++ b/mm/kasan/generic.c > @@ -36,6 +36,17 @@ > #include "kasan.h" > #include "../slab.h" > > +/* > + * Initialize Generic KASAN and enable runtime checks. > + * This should be called from arch kasan_init() once shadow memory is ready. > + */ > +void __init kasan_init_generic(void) > +{ > + kasan_enable(); > + > + pr_info("KernelAddressSanitizer initialized (generic)\n"); > +} > + > /* > * All functions below always inlined so compiler could > * perform better optimizations in each of __asan_loadX/__assn_storeX > diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c > index 9a6927394b5..c8289a3feab 100644 > --- a/mm/kasan/hw_tags.c > +++ b/mm/kasan/hw_tags.c > @@ -45,13 +45,6 @@ static enum kasan_arg kasan_arg __ro_after_init; > static enum kasan_arg_mode kasan_arg_mode __ro_after_init; > static enum kasan_arg_vmalloc kasan_arg_vmalloc __initdata; > > -/* > - * Whether KASAN is enabled at all. > - * The value remains false until KASAN is initialized by kasan_init_hw_tags(). > - */ > -DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled); > -EXPORT_SYMBOL(kasan_flag_enabled); > - > /* > * Whether the selected mode is synchronous, asynchronous, or asymmetric. > * Defaults to KASAN_MODE_SYNC. > @@ -260,7 +253,7 @@ void __init kasan_init_hw_tags(void) > kasan_init_tags(); > > /* KASAN is now initialized, enable it. */ > - static_branch_enable(&kasan_flag_enabled); > + kasan_enable(); > This is obviously broken for the HW_TAGS case. kasan_enable() does nothing, and kasan_hw_tags_enabled() now always return true.