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h=Date:From:To:Cc:Subject:References:In-Reply-To; b=R4EQdXBNX8QLXGc0X8TmBH9Fb9wWbqf+Oyh7f7jwj4AQpxv0TaRTM+7oBwtj9pXcT kufcOzg4jPz6GRNP+iX6tFOWBfsU1mAYaGgqHYG2KRsiM14/+4ZLjO7CJBikdSMBpJ wVkiA3Y5wG7dEInpGmZFZ2JLXRYrEJFIGjxAMD5eqBw8yBcxEEyJxPAfr+XSZE/98X 0AwNwjGi479VRMBjZkIVFsZ8kiCCML/MQmWVQtHlS9ylY4ZS1f21kzS1cLumk073Lw Ve0mbW/MPWGakjeHzDS4YCtvvKb4rP50KyXWyYkP0gtn7AIbRYA/mJFlm4a2Soau1B EBx8vWbmq8Zmg== Date: Fri, 30 Oct 2026 21:13:30 -0700 From: Kees Cook To: Chris Down Cc: Vlastimil Babka , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Marco Elver , GONG Ruiqi , Jonathan Corbet , linux-mm@kvack.org, linux-hardening@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v2 1/6] mm/slab: Enable SLAB_FREELIST_HARDENED by default Message-ID: <202610302112.453CE16119@keescook> References: <2ba9dc862607d70050bbc86fce0091de2e23c023.1793253633.git.chris@chrisdown.name> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2ba9dc862607d70050bbc86fce0091de2e23c023.1793253633.git.chris@chrisdown.name> X-Rspam-User: X-Rspamd-Queue-Id: 1051E20002 X-Stat-Signature: s76ae7zisif6sxdrg949uyeeh9ndiomg X-Rspamd-Server: rspam01 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793420011-770814 X-HE-Meta: U2FsdGVkX1+QpoSt5BjcVchnLGpmbToy2Lilll3+dztCsTZ7UPPjFiHrJaEG5PhVczpjaXAcQ1cUBY7gnm1C18HoO0acEdvZJTDrl+2hJ7XrVUfgmBvCQmMFZPM4VQhymdBtiAwJ1rGRNqWF6pvLEvcTUO+9pGAHbiAoi4CWara95j3jZwnGC9ZtyFEhGWA1Okd8qbwVFrninD051C8bwk1jd30WvAl3UdZmvJUmkOsbFRz2HVFsJdoLpYSPs0pfFHsFJxEEp7akryPSAOd001OjDXr+HKrjaX6gyaGImREj7u7fx76Oc3sPVcEfKXqYwB1kf1RTtiZhoD10H1zoKeGQ/EptoPHo/LyKkf1isZ/CcHCPyYm6POGLRbpuivQEGAekIn9w8DIcJLqXeHvV/bWMcBHhfAr1KYpyxQ0OdIP0OdRlWQr5yHBtL5WyZrpoHQf934aQV/ZH/5XlRJXf441CBqHETOlF0vpH+oVizwGf+eYdytvdsRM2+R7rlMrxwSpXBzdeeXIKS2F18vvESGQaXC2w02gdleyxUmC7P/64sYtBCEf86dlMTrGe4a+w6ahkLgGQalPVtiokabliz0pFQRHhYSlAzUVZN0jhC7a9FIp6ZnP43Ky+QfmZod687S2gwaLs6aBEm0cvKyWvIFeX5hBoDFbd7fEeIGC4yM7AkyH6VqX3mclOA9Cre+ZrldSfpykaCg5N8xrskVZ7r/fwSziX3s1vKTLDvEQeatkgrcKRjZFaoT/SNOzy1QhBuvYsmjzTTf/O8uD4NUssvg/IAVp15rRHiVGZBR4fi/HvZge1IHrD0D2nhQ+0HtT2sFW+mcd+l8fOWHcUPtTHH86Tdbih5WWWg89CB2H0MJcbXlP5YMY2RR0sJm8MVFF/xoUac66TT49Kbdusbuwb9Vpq/Zr+aZy144GohBGrlzuPji1kqShvv22f+HbQ2WC4eEMfEJmUaWHkMbWql2u usyBAQrd HK1sT+pAV29bovdiaNwX1SUdtJFIc3btWufdpNiFyLSLscH7GoNy9/T73XWpUMF4jLYt2R2AdNe8zTJPQt78WUjEYm32cmcXrjvC8LW8Cr/D9TNLrd4aQMcYPSpw3lTVOUX+pBPh83Fsh+lPeEUIWgA515wTyrJpYkeaZ1f7/Gg7yI8EHJ5r1Q6fk527nK2cS8/h6HZeB068M/1XR3FElWnHKZJcBuVdZbByKjYtoXheIPkWrVBWILb0eZ/ZMZVtRYVebtJhWOhjC4ySWsiU2mdxdM3VJF4DVJPwPtBC2h7me1tWu8X5hKBpZSVBJesVE6GDI Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu, Oct 29, 2026 at 02:07:22PM +0800, Chris Down wrote: > SLAB_FREELIST_HARDENED obfuscates the free pointers stored in free > objects, and catches naive double frees and frees to the wrong cache. > Most distros already enable it, and with sheaves its cost is small, > since the per-cpu fast paths don't touch freelists. Measurements also > show this quite clearly [1][2]. > > So let's just enable it by default. SLAB_BUCKETS defaults to > SLAB_FREELIST_HARDENED, so it's now enabled by default too. > > Link: https://lore.kernel.org/all/auITixAJMfLtfa7i@chrisdown.name/ [1] > Link: https://lore.kernel.org/all/179312451613.474906.1475329637924619088@kernel.org/ [2] > Suggested-by: Vlastimil Babka > Signed-off-by: Chris Down Like I've always wanted it. :) Reviewed-by: Kees Cook -- Kees Cook