From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.14]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E597E299959; Mon, 19 Jan 2026 16:10:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.14 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768839046; cv=none; b=pJiObgD/YWGP2F0RHAvvmkCxLgVttOqON02wd1Lbiqg5R2q4hQSWoS9ZInGgUE81GvBSF/J+c2NacPpMFYcDcq+bUnHjnSy9bmQPc48a/+VWs7nuvIX36DgfM3Ej1fg/SlGFJE73wPncGQyvg0LX0cXAHXemthjaQ8j8K76u03M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768839046; c=relaxed/simple; bh=dPaEw2aa5u0SVM5+XwHOK0y6nSiExAWMwRY/JJ5VvQ4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=T1W3ICV05j6nX/hTXNl8pWhLsZ8uC9WBBpQKyRKdGM642WSYSrN/yKBI7lET8zwH98bXgqj/fGmEfWs/zSKsCUd7SteRv1WINUPW0rPX9IXTbRPKxqcekfcj2Kr6ihY80qp7Q2D5+kipmvptinbP0pH0GEpI7gWSO59yLxzcsIg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=k+PIHz9I; arc=none smtp.client-ip=198.175.65.14 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="k+PIHz9I" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1768839045; x=1800375045; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=dPaEw2aa5u0SVM5+XwHOK0y6nSiExAWMwRY/JJ5VvQ4=; b=k+PIHz9I8Orj1wctlZeRofEqBMCeaA2Zh+3LsKp/jVCC8CM84puvCQwa 3d797mBm5LD6W/9AL3m2hZOFGFNsS4gNuWRbcBK70VDnV+/kmVNK37SRi QX23supjR+fOLnCHoP+CFDbarryon807RV8onJuscq1nJqSXn66GCW39j xvyWKoqlGUZOiwP6/RTA6S51ThBzTMp5NFD46Y+fn7UKb6jPGcCFIzc4q oXls8eSXJtkWOim+bXey97f8uuOzY6MD30fOkSdtZQMAcfhi8Pgfl77Xj XbqdDdt4vZWaKn/Mm9p7lRkzuIIGvIm/l8ajuHedkct6f+VAoWBUpi8cw A==; X-CSE-ConnectionGUID: nOReYuNQQL+Wojau+UXpzQ== X-CSE-MsgGUID: sbTNt0k1TBqM3YtdhcMoiQ== X-IronPort-AV: E=McAfee;i="6800,10657,11676"; a="73906851" X-IronPort-AV: E=Sophos;i="6.21,238,1763452800"; d="scan'208";a="73906851" Received: from orviesa010.jf.intel.com ([10.64.159.150]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Jan 2026 08:10:44 -0800 X-CSE-ConnectionGUID: EjVT2CTdSL+iBJ4OGRaOlQ== X-CSE-MsgGUID: 8Px4MFfoQeC7IU/aMGjpQQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,238,1763452800"; d="scan'208";a="205150360" Received: from cjhill-mobl.amr.corp.intel.com (HELO [10.125.111.233]) ([10.125.111.233]) by orviesa010-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Jan 2026 08:10:43 -0800 Message-ID: <85d0d013-eca2-4b9f-bee3-d583d0eeb99e@intel.com> Date: Mon, 19 Jan 2026 08:10:42 -0800 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/3] randomize_kstack: Maintain kstack_offset per task To: Ryan Roberts , Catalin Marinas , Will Deacon , Huacai Chen , Madhavan Srinivasan , Michael Ellerman , Paul Walmsley , Palmer Dabbelt , Albert Ou , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Kees Cook , "Gustavo A. R. Silva" , Arnd Bergmann , Mark Rutland , "Jason A. Donenfeld" , Ard Biesheuvel , Jeremy Linton , David Laight Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-hardening@vger.kernel.org, stable@vger.kernel.org References: <20260119130122.1283821-1-ryan.roberts@arm.com> <20260119130122.1283821-2-ryan.roberts@arm.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: <20260119130122.1283821-2-ryan.roberts@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/19/26 05:01, Ryan Roberts wrote: ... > Cc: stable@vger.kernel.org Since this doesn't fix any known functional issues, if it were me, I'd leave stable@ alone. It isn't clear that this is stable material. > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1591,6 +1591,10 @@ struct task_struct { > unsigned long prev_lowest_stack; > #endif > > +#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET > + u32 kstack_offset; > +#endif > + > #ifdef CONFIG_X86_MCE > void __user *mce_vaddr; Nit: This seems to be throwing a u32 potentially in between a couple of void*/ulong sized objects. It probably doesn't matter with struct randomization and it's really hard to get right among the web of task_struct #ifdefs. But, it would be nice to at _least_ nestle this next to another int-sized thing. Does it really even need to be 32 bits? x86 has this comment: > /* > * This value will get limited by KSTACK_OFFSET_MAX(), which is 10 > * bits. The actual entropy will be further reduced by the compiler > * when applying stack alignment constraints (see cc_stack_align4/8 in > * arch/x86/Makefile), which will remove the 3 (x86_64) or 2 (ia32) > * low bits from any entropy chosen here. > * > * Therefore, final stack offset entropy will be 7 (x86_64) or > * 8 (ia32) bits. > */