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Wed, 31 Jul 2024 14:30:35 +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 mySoHotKqmbIdAAAD6G6ig (envelope-from ); Wed, 31 Jul 2024 14:30:35 +0000 Message-ID: Date: Wed, 31 Jul 2024 16:30:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: krealloc: consider spare memory for __GFP_ZERO Content-Language: en-US To: Danilo Krummrich Cc: akpm@linux-foundation.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev References: <20240730194214.31483-1-dakr@kernel.org> <66836dd6-b0c2-4f77-b2a3-c43296aa6c93@suse.cz> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spamd-Bar: / X-Rspamd-Action: no action X-Stat-Signature: e6uxane35i9kwwc9n4rgbfxppqts8oeo X-Rspamd-Queue-Id: A365B20030 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1722436237-126475 X-HE-Meta: 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 OZGtXLfZ sEuAM5VgGwCnVNoruRVYv5kqH6CNUTaRv1RRjGYI2SvrNXIzI2OlaWd2/P/FslKLD4GyG1c9pS7CCU6Od8DJK6dba0a8EnBaJd0YgLD30B2bPg0IR6o2qEV8ZvynAOD2mvYJ3OiKf2XmjSf0BPzE4D4dXnKHbHTTjZgWgnemYXxPy18CbZDKnRgoctYqQpwN+dOr7Y2Yfa+y7ASOjnWHh6e3mGuGLYRDR1fnUxm2B9WzgqjsJhlIsUeJyLXoXeihJNAi9j20LCGRj0klY7g44OeXQ0Opzbro6WaEVyUtxuAUkfsWfj0Z8ZvBtVn88oc7nha8HJisbd5uccorPM2eNYKqIrsVsAIObQwQa6YP5SzsmXmACnAEK06Yq4VTzKhs0Hgovy6WjFlGiEYe8UFYWNZY0qmoLsn9QTYWW812WwI++Rn1lmT0uF3IMHA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000011, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/31/24 1:54 AM, Danilo Krummrich wrote: > On Tue, Jul 30, 2024 at 11:14:16PM +0200, Vlastimil Babka wrote: >> On 7/30/24 9:42 PM, Danilo Krummrich wrote: >> > As long as krealloc() is called with __GFP_ZERO consistently, starting >> > with the initial memory allocation, __GFP_ZERO should be fully honored. >> > >> > However, if for an existing allocation krealloc() is called with a >> > decreased size, it is not ensured that the spare portion the allocation >> > is zeroed. Thus, if krealloc() is subsequently called with a larger size >> > again, __GFP_ZERO can't be fully honored, since we don't know the >> > previous size, but only the bucket size. >> > >> > Example: >> > >> > buf = kzalloc(64, GFP_KERNEL); >> > memset(buf, 0xff, 64); >> > >> > buf = krealloc(buf, 48, GFP_KERNEL | __GFP_ZERO); >> > >> > /* After this call the last 16 bytes are still 0xff. */ >> > buf = krealloc(buf, 64, GFP_KERNEL | __GFP_ZERO); >> > >> > Fix this, by explicitly setting spare memory to zero, when shrinking an >> > allocation with __GFP_ZERO flag set or init_on_alloc enabled. >> > >> > Signed-off-by: Danilo Krummrich >> > --- >> > mm/slab_common.c | 7 +++++++ >> > 1 file changed, 7 insertions(+) >> > >> > diff --git a/mm/slab_common.c b/mm/slab_common.c >> > index 40b582a014b8..cff602cedf8e 100644 >> > --- a/mm/slab_common.c >> > +++ b/mm/slab_common.c >> > @@ -1273,6 +1273,13 @@ __do_krealloc(const void *p, size_t new_size, gfp_t flags) >> > >> > /* If the object still fits, repoison it precisely. */ >> > if (ks >= new_size) { >> > + /* Zero out spare memory. */ >> > + if (want_init_on_alloc(flags)) { >> > + kasan_disable_current(); >> > + memset((void *)p + new_size, 0, ks - new_size); >> > + kasan_enable_current(); >> >> If we do kasan_krealloc() first, shouldn't the memset then be legal >> afterwards without the disable/enable dance? > > No, we always write into the poisoned area. The following tables show what we do > in the particular case: > > Shrink > ------ > new old > 0 size size ks > |----------|----------|----------| > | keep | poison | <- poison > |--------------------------------| > | keep | zero | <- data > > > Poison and zero things between old size and ks is not necessary, but we don't > know old size, hence we have do it between new size and ks. > > Grow > ---- > old new > 0 size size ks > |----------|----------|----------| > | unpoison | keep | <- poison > |--------------------------------| > | keep | zero | <- data > > Zeroing between new_size and ks in not necessary in this case, since it must be > zero already. But without knowing the old size we don't know whether we shrink > and actually need to do something, or if we grow and don't need to do anything. > > Analogously, we also unpoison things between 0 and old size for the same reason. Thanks, you're right! >> >> > + } >> > + >> > p = kasan_krealloc((void *)p, new_size, flags); >> > return (void *)p; >> > } >> > >> > base-commit: 7c3dd6d99f2df6a9d7944ee8505b195ba51c9b68 >>