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Tue, 09 Feb 2021 05:24:49 -0800 (PST) MIME-Version: 1.0 References: <9bef90327c9cb109d736c40115684fd32f49e6b0.1612546384.git.andreyknvl@google.com> In-Reply-To: From: Andrey Konovalov Date: Tue, 9 Feb 2021 14:24:38 +0100 Message-ID: Subject: Re: [PATCH v3 mm 08/13] kasan, mm: optimize krealloc poisoning To: Marco Elver Cc: Andrew Morton , Catalin Marinas , Vincenzo Frascino , Dmitry Vyukov , Alexander Potapenko , Will Deacon , Andrey Ryabinin , Peter Collingbourne , Evgenii Stepanov , Branislav Rankov , Kevin Brodsky , kasan-dev , Linux ARM , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0BF8EC0001DC X-Stat-Signature: pokzt56yfipnp76iwj6im8iueysacrc6 Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf06; identity=mailfrom; envelope-from=""; helo=mail-pl1-f180.google.com; client-ip=209.85.214.180 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612877571-70686 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 Mon, Feb 8, 2021 at 11:48 AM Marco Elver wrote: > > On Fri, Feb 05, 2021 at 06:34PM +0100, Andrey Konovalov wrote: > > Currently, krealloc() always calls ksize(), which unpoisons the whole > > object including the redzone. This is inefficient, as kasan_krealloc() > > repoisons the redzone for objects that fit into the same buffer. > > > > This patch changes krealloc() instrumentation to use uninstrumented > > __ksize() that doesn't unpoison the memory. Instead, kasan_kreallos() > > is changed to unpoison the memory excluding the redzone. > > > > For objects that don't fit into the old allocation, this patch disables > > KASAN accessibility checks when copying memory into a new object instead > > of unpoisoning it. > > > > Signed-off-by: Andrey Konovalov > > Reviewed-by: Marco Elver > > Clarification below. > > > --- > > mm/kasan/common.c | 12 ++++++++++-- > > mm/slab_common.c | 20 ++++++++++++++------ > > 2 files changed, 24 insertions(+), 8 deletions(-) > > > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > > index 7ea643f7e69c..a8a67dca5e55 100644 > > --- a/mm/kasan/common.c > > +++ b/mm/kasan/common.c > > @@ -476,7 +476,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object, > > > > /* > > * The object has already been unpoisoned by kasan_slab_alloc() for > > - * kmalloc() or by ksize() for krealloc(). > > + * kmalloc() or by kasan_krealloc() for krealloc(). > > */ > > > > /* > > @@ -526,7 +526,7 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size, > > > > /* > > * The object has already been unpoisoned by kasan_alloc_pages() for > > - * alloc_pages() or by ksize() for krealloc(). > > + * alloc_pages() or by kasan_krealloc() for krealloc(). > > */ > > > > /* > > @@ -554,8 +554,16 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag > > if (unlikely(object == ZERO_SIZE_PTR)) > > return (void *)object; > > > > + /* > > + * Unpoison the object's data. > > + * Part of it might already have been unpoisoned, but it's unknown > > + * how big that part is. > > + */ > > + kasan_unpoison(object, size); > > + > > page = virt_to_head_page(object); > > > > + /* Piggy-back on kmalloc() instrumentation to poison the redzone. */ > > if (unlikely(!PageSlab(page))) > > return __kasan_kmalloc_large(object, size, flags); > > else > > diff --git a/mm/slab_common.c b/mm/slab_common.c > > index dad70239b54c..60a2f49df6ce 100644 > > --- a/mm/slab_common.c > > +++ b/mm/slab_common.c > > @@ -1140,19 +1140,27 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size, > > void *ret; > > size_t ks; > > > > - if (likely(!ZERO_OR_NULL_PTR(p)) && !kasan_check_byte(p)) > > - return NULL; > > - > > - ks = ksize(p); > > + /* Don't use instrumented ksize to allow precise KASAN poisoning. */ > > + if (likely(!ZERO_OR_NULL_PTR(p))) { > > + if (!kasan_check_byte(p)) > > + return NULL; > > Just checking: Check byte returns true if the object is not tracked by KASAN, right? I.e. if it's a KFENCE object, kasan_check_byte() always returns true. kasan_check_byte() still performs the check, but since KFENCE objects are never poisoned, the check always passes. Thanks!