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b=t0YPJ+tRu7KQvvMWn+FqGf7Ds8NiCGKgObBP/DOHBxKqAXzkTMINok/izr/CIvgFp h7314WElslBeOUoScNRuw+2QiRvqcjPq2cstDU6KK/7YxCW6dNSjtIFOmMTmyuUn4o sT9BE4zvuQQtxhwMD/WHfwXOe2BpUj0wzzlrMaJfqmUVl4Ryl8hGjc6zaiZgaT0lWk 321jEKHdUeRMG7S/Ecv2EGrBNSKWEHC5P/4pP8MZtLf6tQAk7DVhjv7BCwDmDK/a8P aewo8jJuljk4xDCjbSFNN/YMeyJsc87NYkGn9oQQ7IteDwmIjFtIvhgv3vzEuOe5A/ gdoxBcI2JRTSw== Date: Fri, 31 May 2024 09:39:48 -0700 From: Kees Cook To: Kent Overstreet Cc: Vlastimil Babka , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, "GONG, Ruiqi" , Xiu Jianfeng , Suren Baghdasaryan , Jann Horn , Matteo Rizzo , Thomas Graf , Herbert Xu , julien.voisin@dustri.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v3 0/6] slab: Introduce dedicated bucket allocator Message-ID: <202405310938.A6EFEADB79@keescook> References: <20240424213019.make.366-kees@kernel.org> <7nonr2cucww7j55kresncgt23pvgt3pmnfukqpnqblk3fmtfdl@ewhqe3ylioz2> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7nonr2cucww7j55kresncgt23pvgt3pmnfukqpnqblk3fmtfdl@ewhqe3ylioz2> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2973B40009 X-Stat-Signature: ywf4gio9bydbqh3s67941kwki1yi9o6i X-HE-Tag: 1717173592-117290 X-HE-Meta: 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 dGBvftsl 3idSAejnbtLeh4K9glN0XlOcvw12Ej+TqIYKBzVJf153oGP0sdPvtcE3GiyLqVVlO4izZC1O7uN/tKjDtjZ2TkcI3xd10LdqqrJBB+LPccbPWWTDjguzs3eWiax66tqpsNMUNk0S1CSHH9mfpRpp+RtdvYowtfGHRrFDKiPG8nl2GJlYBNf2NWVhWgH6A0r0NFEKGh5zG1X6wyyJLtOsL+UqLlqGGvWj5WoxY0O2GL4z1c3orU2WLW1GGYE7mN3C45RvFA1bnnJqC+AZkf3JCvjAoWNZ////p0Tin3Tbqgyaq3XCysdON27Gc8eUKZrfJ9ZUH 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 Fri, May 24, 2024 at 10:54:58AM -0400, Kent Overstreet wrote: > On Wed, Apr 24, 2024 at 02:40:57PM -0700, Kees Cook wrote: > > Hi, > > > > Series change history: > > > > v3: > > - clarify rationale and purpose in commit log > > - rebase to -next (CONFIG_CODE_TAGGING) > > - simplify calling styles and split out bucket plumbing more cleanly > > - consolidate kmem_buckets_*() family introduction patches > > v2: https://lore.kernel.org/lkml/20240305100933.it.923-kees@kernel.org/ > > v1: https://lore.kernel.org/lkml/20240304184252.work.496-kees@kernel.org/ > > > > For the cover letter, I'm repeating commit log for patch 4 here, which has > > additional clarifications and rationale since v2: > > > > Dedicated caches are available for fixed size allocations via > > kmem_cache_alloc(), but for dynamically sized allocations there is only > > the global kmalloc API's set of buckets available. This means it isn't > > possible to separate specific sets of dynamically sized allocations into > > a separate collection of caches. > > > > This leads to a use-after-free exploitation weakness in the Linux > > kernel since many heap memory spraying/grooming attacks depend on using > > userspace-controllable dynamically sized allocations to collide with > > fixed size allocations that end up in same cache. > > This is going to increase internal fragmentation in the slab allocator, > so we're going to need better, more visible numbers on the amount of > memory stranded thusly, so users can easily see the effect this has. Yes, but not significantly. It's less than the 16-buckets randomized kmalloc implementation. The numbers will be visible in /proc/slabinfo just like any other. > Please also document this effect and point users in the documentation > where to check, so that we devs can get feedback on this. Okay, sure. In the commit log, or did you have somewhere else in mind? -- Kees Cook