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Wed, 30 Jun 2021 12:13:35 -0700 (PDT) Received: from elver.google.com ([2a00:79e0:15:13:8b0e:c57f:ff29:7e4]) by smtp.gmail.com with ESMTPSA id o20sm6991115wms.3.2021.06.30.12.13.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Jun 2021 12:13:34 -0700 (PDT) Date: Wed, 30 Jun 2021 21:13:27 +0200 From: Marco Elver To: yee.lee@mediatek.com Cc: andreyknvl@gmail.com, wsd_upstream@mediatek.com, Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , Andrew Morton , Matthias Brugger , "open list:KASAN" , "open list:MEMORY MANAGEMENT" , open list , "moderated list:ARM/Mediatek SoC support" , "moderated list:ARM/Mediatek SoC support" Subject: Re: [PATCH v3 1/1] kasan: Add memzero init for unaligned size under SLUB debug Message-ID: References: <20210630134943.20781-1-yee.lee@mediatek.com> <20210630134943.20781-2-yee.lee@mediatek.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210630134943.20781-2-yee.lee@mediatek.com> User-Agent: Mutt/2.0.5 (2021-01-21) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=r7y6xbzz; spf=pass (imf18.hostedemail.com: domain of elver@google.com designates 209.85.221.54 as permitted sender) smtp.mailfrom=elver@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D7A4F400208D X-Stat-Signature: agfnjg91zrktubymcxay4uttdhruontr X-HE-Tag: 1625080416-332716 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jun 30, 2021 at 09:49PM +0800, yee.lee@mediatek.com wrote: > From: Yee Lee > > Issue: when SLUB debug is on, hwtag kasan_unpoison() would overwrite > the redzone of object with unaligned size. > > An additional memzero_explicit() path is added to replacing init by > hwtag instruction for those unaligned size at SLUB debug mode. > > The penalty is acceptable since they are only enabled in debug mode, > not production builds. A block of comment is added for explanation. > > Signed-off-by: Yee Lee > Suggested-by: Marco Elver > Suggested-by: Andrey Konovalov > Cc: Andrey Ryabinin > Cc: Alexander Potapenko > Cc: Dmitry Vyukov > Cc: Andrew Morton In future, please add changes to each version after an additional '---'. Example: --- v2: * Use IS_ENABLED(CONFIG_SLUB_DEBUG) in if-statement. > --- > mm/kasan/kasan.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > index 8f450bc28045..6f698f13dbe6 100644 > --- a/mm/kasan/kasan.h > +++ b/mm/kasan/kasan.h > @@ -387,6 +387,16 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init) > > if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK)) > return; > + /* > + * Explicitly initialize the memory with the precise object size > + * to avoid overwriting the SLAB redzone. This disables initialization > + * in the arch code and may thus lead to performance penalty. > + * The penalty is accepted since SLAB redzones aren't enabled in production builds. > + */ Can we please format the comment properly: diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index 6f698f13dbe6..1972ec5736cb 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -388,10 +388,10 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init) if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK)) return; /* - * Explicitly initialize the memory with the precise object size - * to avoid overwriting the SLAB redzone. This disables initialization - * in the arch code and may thus lead to performance penalty. - * The penalty is accepted since SLAB redzones aren't enabled in production builds. + * Explicitly initialize the memory with the precise object size to + * avoid overwriting the SLAB redzone. This disables initialization in + * the arch code and may thus lead to performance penalty. The penalty + * is accepted since SLAB redzones aren't enabled in production builds. */ if (IS_ENABLED(CONFIG_SLUB_DEBUG) && init && ((unsigned long)size & KASAN_GRANULE_MASK)) { init = false; > + if (IS_ENABLED(CONFIG_SLUB_DEBUG) && init && ((unsigned long)size & KASAN_GRANULE_MASK)) { > + init = false; > + memzero_explicit((void *)addr, size); > + } > size = round_up(size, KASAN_GRANULE_SIZE); > > hw_set_mem_tag_range((void *)addr, size, tag, init); I think this solution might be fine for now, as I don't see an easy way to do this without some major refactor to use kmem_cache_debug_flags(). However, I think there's an intermediate solution where we only check the static-key 'slub_debug_enabled' though. Because I've checked, and various major distros _do_ enabled CONFIG_SLUB_DEBUG. But the static branch just makes sure there's no performance overhead. Checking the static branch requires including mm/slab.h into mm/kasan/kasan.h, which we currently don't do and perhaps wanted to avoid. Although I don't see a reason there, because there's no circular dependency even if we did. Andrey, any opinion? In case you guys think checking static key is the better solution, I think the below would work together with the pre-requisite patch at the end: diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index 1972ec5736cb..9130d025612c 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -6,6 +6,8 @@ #include #include +#include "../slab.h" + #ifdef CONFIG_KASAN_HW_TAGS #include @@ -393,7 +395,8 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init) * the arch code and may thus lead to performance penalty. The penalty * is accepted since SLAB redzones aren't enabled in production builds. */ - if (IS_ENABLED(CONFIG_SLUB_DEBUG) && init && ((unsigned long)size & KASAN_GRANULE_MASK)) { + if (slub_debug_enabled_unlikely() && + init && ((unsigned long)size & KASAN_GRANULE_MASK)) { init = false; memzero_explicit((void *)addr, size); } [ Note: You can pick the below patch up by extracting it from the email and running 'git am -s '. You could then use it as part of a patch series together with your original patch. ] From: Marco Elver Date: Wed, 30 Jun 2021 20:56:57 +0200 Subject: [PATCH] mm: introduce helper to check slub_debug_enabled Introduce a helper to check slub_debug_enabled, so that we can confine the use of #ifdef to the definition of the slub_debug_enabled_unlikely() helper. Signed-off-by: Marco Elver --- mm/slab.h | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/mm/slab.h b/mm/slab.h index 18c1927cd196..9439da434712 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -215,10 +215,18 @@ DECLARE_STATIC_KEY_TRUE(slub_debug_enabled); DECLARE_STATIC_KEY_FALSE(slub_debug_enabled); #endif extern void print_tracking(struct kmem_cache *s, void *object); +static inline bool slub_debug_enabled_unlikely(void) +{ + return static_branch_unlikely(&slub_debug_enabled); +} #else static inline void print_tracking(struct kmem_cache *s, void *object) { } +static inline bool slub_debug_enabled_unlikely(void) +{ + return false; +} #endif /* @@ -228,11 +236,10 @@ static inline void print_tracking(struct kmem_cache *s, void *object) */ static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t flags) { -#ifdef CONFIG_SLUB_DEBUG - VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS)); - if (static_branch_unlikely(&slub_debug_enabled)) + if (IS_ENABLED(CONFIG_SLUB_DEBUG)) + VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS)); + if (slub_debug_enabled_unlikely()) return s->flags & flags; -#endif return false; } -- 2.32.0.93.g670b81a890-goog