From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.7]) (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 3EC831D63E8 for ; Mon, 21 Jul 2025 22:33:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.7 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753137214; cv=none; b=ruKYhUN+KXkHLnEiIhzvUEgTLXRO4bm0TCmrAhkMphmUf5E+R6vQWfgL6c3tIignID5xayMqKXEklTEnjMuWG3BOcvS6F8nC6k6Pf3roxFh//NaAcONR1bivdg3Njq3opIfccAwMJjTJ3QNHUoGzVN4rGt4A4yho5XxBbfRD9m0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753137214; c=relaxed/simple; bh=j+5u8vKRU9Y5ARArhCBRv5xODAIyRFp69Xa+IjrJT14=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cGr2cWe3t5Gm6lD6bZFiBrCRSNN9SlDXTXKR22WZVB5ASQ23kIXhzLCSHihdUfqRQVE7Kq0flaXWUx5sHTAoC2Lqgu9hW93SIBHhKXRRk0yjDSFvd0GzWzdZqLNuThee25bupO54yQQK3TURxaH2j5KOsz9GY0iUtYxxjeI4N2Q= 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=cKyn+GZC; arc=none smtp.client-ip=192.198.163.7 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="cKyn+GZC" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1753137212; x=1784673212; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=j+5u8vKRU9Y5ARArhCBRv5xODAIyRFp69Xa+IjrJT14=; b=cKyn+GZCjrky3P+YL4FnDc27nX5lVzR68J0bh86vFAkkhM26lFZEwMZB vhHN8mFA08Oebs3MnpxTTPyTmrW5nNEI4tF4Zf4RHkJc8eyrsGBqjMNIV m+qGLitP0qPtrvjT6LSJuBv+bbyr7gUgUkwHOLQpIFdMBvDF+nSubmxN7 IZprYE620JMwnb0+sEkLlb2neDO37aGncIq0t5xRD4nW7w6GngrxCm7TO 2SNGle8FuIof1DGw/jNq6308eFDqBqavX14uxBB5OMATYv1Wa9qgszEl3 /Vb0HLQAwf9IfawY3fx6fLPUePnpIrg3npnMTXOFvurbVySUhCdQhpK9J Q==; X-CSE-ConnectionGUID: qeDZ3OirQYa06cqNemFOCQ== X-CSE-MsgGUID: jsXSEqBjTjGSrEO48FKg6Q== X-IronPort-AV: E=McAfee;i="6800,10657,11499"; a="80814900" X-IronPort-AV: E=Sophos;i="6.16,330,1744095600"; d="scan'208";a="80814900" Received: from orviesa010.jf.intel.com ([10.64.159.150]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Jul 2025 15:33:31 -0700 X-CSE-ConnectionGUID: soMqseb9QdW5t9kHBULtWQ== X-CSE-MsgGUID: vSW18LGcRaScKZjc4XClvA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,330,1744095600"; d="scan'208";a="158264433" Received: from jdoman-mobl3.amr.corp.intel.com (HELO [10.125.108.89]) ([10.125.108.89]) by orviesa010-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Jul 2025 15:33:30 -0700 Message-ID: <9d02685f-5c19-47d4-8f7f-bb546c0c7504@intel.com> Date: Mon, 21 Jul 2025 15:33:30 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] x86/fpu: Fix NULL dereference in avx512_status() To: Sohil Mehta , Dave Hansen , x86@kernel.org Cc: Borislav Petkov , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , Sean Christopherson , Peter Zijlstra , Vignesh Balasubramanian , Rick Edgecombe , Oleg Nesterov , "Chang S . Bae" , Brian Gerst , Eric Biggers , Kees Cook , Chao Gao , Fushuai Wang , linux-kernel@vger.kernel.org References: <20250721215302.3562784-1-sohil.mehta@intel.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: <20250721215302.3562784-1-sohil.mehta@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/21/25 14:53, Sohil Mehta wrote: > From: Fushuai Wang > > When CONFIG_X86_DEBUG_FPU is set, reading /proc/[kthread]/arch_status > causes a NULL pointer dereference. > > For Kthreads tasks: > proc_pid_arch_status() > avx512_status() > x86_task_fpu() => returns NULL when CONFIG_X86_DEBUG_FPU=y > x86_task_fpu()->avx512_timestamp => NULL dereference This seems to imply that CONFIG_X86_DEBUG_FPU _triggers_ the bug. It certainly makes it obvious, but isn't there a bug with or without CONFIG_X86_DEBUG_FPU? Even without it, I think it'll access out of the init_task bounds. > Kernel threads aren't expected to access FPU state directly. However, > avx512_timestamp resides within struct fpu which lead to this unique > situation. What does this mean? Most kernel threads have a 'struct fpu', right? > It is uncertain whether kernel threads use AVX-512 in a meaningful way > that needs userspace reporting. For now, avoid reporting AVX-512 usage > for kernel threads. It would be idea if this was more explicit about how this changes the ABI for kernel threads. Could we make this more precise, please? Report "AVX512_elapsed_ms: -1" for kernel tasks, whether they use AVX-512 or not. This is the same value that is reported for user tasks which have not been detected using AVX-512. > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c > index 9aa9ac8399ae..a75077c645b6 100644 > --- a/arch/x86/kernel/fpu/xstate.c > +++ b/arch/x86/kernel/fpu/xstate.c > @@ -1855,19 +1855,18 @@ long fpu_xstate_prctl(int option, unsigned long arg2) > #ifdef CONFIG_PROC_PID_ARCH_STATUS > /* > * Report the amount of time elapsed in millisecond since last AVX512 > - * use in the task. > + * use in the task. Report -1 if no AVX-512 usage. > */ > static void avx512_status(struct seq_file *m, struct task_struct *task) > { > - unsigned long timestamp = READ_ONCE(x86_task_fpu(task)->avx512_timestamp); > - long delta; > + unsigned long timestamp = 0; > + long delta = -1; > > - if (!timestamp) { > - /* > - * Report -1 if no AVX512 usage > - */ > - delta = -1; > - } else { > + /* Do not report AVX-512 usage for kernel threads */ > + if (!(task->flags & (PF_KTHREAD | PF_USER_WORKER))) > + timestamp = READ_ONCE(x86_task_fpu(task)->avx512_timestamp); > + > + if (timestamp) { > delta = (long)(jiffies - timestamp); > /* > * Cap to LONG_MAX if time difference > LONG_MAX Can we just do: unsigned long timestamp; long delta; if (task->flags & (PF_KTHREAD | PF_USER_WORKER)) return; timestamp = READ_ONCE(x86_task_fpu(task)->avx512_timestamp); ... for now, please? That way, there's no made up value for kernel threads. The value just isn't present in the file.