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Tue, 10 Sep 2024 13:15:36 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id hlbcNXhG4GasGQAAD6G6ig (envelope-from ); Tue, 10 Sep 2024 13:15:36 +0000 Message-ID: Date: Tue, 10 Sep 2024 15:15:36 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] mm/slub: Improve redzone check and zeroing for krealloc() Content-Language: en-US To: Feng Tang , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Andrey Konovalov , Marco Elver , Shuah Khan , David Gow , Danilo Krummrich Cc: linux-mm@kvack.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org References: <20240909012958.913438-1-feng.tang@intel.com> <20240909012958.913438-4-feng.tang@intel.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Level: X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; FREEMAIL_TO(0.00)[intel.com,linux-foundation.org,linux.com,kernel.org,google.com,lge.com,linux.dev,gmail.com,linuxfoundation.org]; TAGGED_RCPT(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_TWELVE(0.00)[16]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; TO_DN_SOME(0.00)[] X-Spam-Score: -2.80 X-Spam-Flag: NO On 9/9/24 03:29, Feng Tang wrote: > For current krealloc(), one problem is its caller doesn't know what's > the actual request size, say the object is 64 bytes kmalloc one, but It's more accurate to say the caller doesn't pass the old size (it might actually know it). > the original caller may only requested 48 bytes. And when krealloc() > shrinks or grows in the same object, or allocate a new bigger object, > it lacks this 'original size' information to do accurate data preserving > or zeroing (when __GFP_ZERO is set). Let's describe the problem specifically by adding: Thus with slub debug redzone and object tracking enabled, parts of the object after krealloc() might contain redzone data instead of zeroes, which is violating the __GFP_ZERO guarantees. > And when some slub debug option is enabled, kmalloc caches do have this > 'orig_size' feature. So utilize it to do more accurate data handling, > as well as enforce the kmalloc-redzone sanity check. > > The krealloc() related code is moved from slab_common.c to slub.c for > more efficient function calling. Agreed with Danilo that having the move as separate preparatory patch would make review easier. Thanks.