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Tue, 2 Jan 2024 16:10:53 +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 f9+XEI01lGWlegAAD6G6ig (envelope-from ); Tue, 02 Jan 2024 16:10:53 +0000 Message-ID: Date: Tue, 2 Jan 2024 17:10:53 +0100 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 v3 15/34] mm: slub: Unpoison the memchr_inv() return value Content-Language: en-US To: Ilya Leoshkevich , Alexander Gordeev , Alexander Potapenko , Andrew Morton , Christoph Lameter , David Rientjes , Heiko Carstens , Joonsoo Kim , Marco Elver , Masami Hiramatsu , Pekka Enberg , Steven Rostedt , Vasily Gorbik Cc: Christian Borntraeger , Dmitry Vyukov , Hyeonggon Yoo <42.hyeyoo@gmail.com>, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Mark Rutland , Roman Gushchin , Sven Schnelle References: <20231213233605.661251-1-iii@linux.ibm.com> <20231213233605.661251-16-iii@linux.ibm.com> From: Vlastimil Babka In-Reply-To: <20231213233605.661251-16-iii@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Score: 1.37 X-Spamd-Result: default: False [1.37 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; XM_UA_NO_VERSION(0.01)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TO_MATCH_ENVRCPT_ALL(0.00)[]; TAGGED_RCPT(0.00)[]; MIME_GOOD(-0.10)[text/plain]; MID_RHS_MATCH_FROM(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RL5nkphuxq5kxo98ppmuqoc8wo)]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; BAYES_HAM(-0.04)[58.94%]; RCPT_COUNT_TWELVE(0.00)[24]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:email]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_CC(0.00)[linux.ibm.com,google.com,gmail.com,googlegroups.com,vger.kernel.org,kvack.org,arm.com,linux.dev]; RCVD_TLS_ALL(0.00)[]; SUSPICIOUS_RECIPS(1.50)[] Authentication-Results: smtp-out1.suse.de; none X-Spam-Level: * X-Spam-Flag: NO On 12/14/23 00:24, Ilya Leoshkevich wrote: > Even though the KMSAN warnings generated by memchr_inv() are suppressed > by metadata_access_enable(), its return value may still be poisoned. > > The reason is that the last iteration of memchr_inv() returns > `*start != value ? start : NULL`, where *start is poisoned. Because of > this, somewhat counterintuitively, the shadow value computed by > visitSelectInst() is equal to `(uintptr_t)start`. > > The intention behind guarding memchr_inv() behind > metadata_access_enable() is to touch poisoned metadata without > triggering KMSAN, so unpoison its return value. > > Signed-off-by: Ilya Leoshkevich Acked-by: Vlastimil Babka > --- > mm/slub.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/slub.c b/mm/slub.c > index 2d29d368894c..802702748925 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -1076,6 +1076,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct slab *slab, > metadata_access_enable(); > fault = memchr_inv(kasan_reset_tag(start), value, bytes); > metadata_access_disable(); > + kmsan_unpoison_memory(&fault, sizeof(fault)); > if (!fault) > return 1; > > @@ -1182,6 +1183,7 @@ static void slab_pad_check(struct kmem_cache *s, struct slab *slab) > metadata_access_enable(); > fault = memchr_inv(kasan_reset_tag(pad), POISON_INUSE, remainder); > metadata_access_disable(); > + kmsan_unpoison_memory(&fault, sizeof(fault)); > if (!fault) > return; > while (end > fault && end[-1] == POISON_INUSE)