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b=eEIOlIPc+JHS5zlVZkivZULuFnL5V2QDbJkwbHDhORZUkNF8FaZmpBr7YKtdNuTuv 2G01+wUQfD47yw1RIA1VrBwACjJDBpYMruEZZafoJRvgYf8Tw7jvX0hlTC2Z9DvcI6 f3fpfSIh2cOHfwAoSZQE9pdoK7wwUIxVIRrs4hekx5i6fB9PVk9eEhdIkV2Ss21suL Q5yq0Qq3UKsKB4bXF3KESelTIUoudMf5qfhziin0t4ADx3LlibnWggPnMaRMyt9Cs6 CJvDezP46dy+N2G6Pg1GHjmra3yFkjBLXKJwacbUry44cpQIk1q1hollMPoEg5/mZv kwfoCnPuTOIzA== Date: Wed, 31 Jul 2024 01:54:17 +0200 From: Danilo Krummrich To: Vlastimil Babka 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 Subject: Re: [PATCH 1/2] mm: krealloc: consider spare memory for __GFP_ZERO Message-ID: References: <20240730194214.31483-1-dakr@kernel.org> <66836dd6-b0c2-4f77-b2a3-c43296aa6c93@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <66836dd6-b0c2-4f77-b2a3-c43296aa6c93@suse.cz> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: CCEA9180005 X-Stat-Signature: p1gep1bn7g41e1e1r4wfkaj738u3f9ma X-HE-Tag: 1722383664-740814 X-HE-Meta: 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 Zm2Oixee MiIu5tjFoif78+jpriM1TLfL6nhl6NcWXyDfuPXEFFCkyeitZII/RgNKsOV8Rq8Dqib4gpGdP3lvRUy5YDYVNuxZSqZllD1d7V8irV9BouCm2oeHu7dg66jlcmvP/lYMiD4tQzafh6muoVP3ZH05pH7IBA9r3J58l93n8DfbfMQ7cKz0eFqGxV9FTLbq3ivp+mp6WBWr6F5aP8fuIWecaLB76Z7/0/og9DrE4LHVII1l8y7maUqspLnC/6OpE1AaPXoqrA0j2P+Xf+pQxEFUVVhbg3ATluQiBhd+91nRoBzYLqIWcWOBlnbVmxn1Ja8KaUEZjW5EqZaVxv/03SuOfz9PtSClvIboEIviOJGXC863Jayc= 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: List-Subscribe: List-Unsubscribe: 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. > > > + } > > + > > p = kasan_krealloc((void *)p, new_size, flags); > > return (void *)p; > > } > > > > base-commit: 7c3dd6d99f2df6a9d7944ee8505b195ba51c9b68 >