From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.15]) (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 CF7C51F942 for ; Mon, 4 Nov 2024 17:16:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730740581; cv=none; b=GISkfXU1E7Iu0Kb9ojk6Q7mTix8ruXraBTqhTxE/umP2dvgNBi1svR0WxqUsSxMAQ+/bJpYFb+JUJ9vUmZulJKXUyyLsmRMAH8O0/PAn1QFPoYPLVM2tsrGAw7IdoMvU8w5x97x40YujVTNsebSba6Yk8IOJ0UcEoIJROytKeno= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730740581; c=relaxed/simple; bh=Eb5XXjTzfvQ6tkw5JWsvQ0JvCQR7aIn4XD4N0WEQGnM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UFsOKvM5viWzKZTxuRbc/wxJXFHIuEcmUGJrI7RLlmsDaSak5r9TuWBX7TFoIuwyW6Vak6OLAdZ7IgYtDSvG9xkcUH8Ms3vxZ5GZiZwNvu01ImMH739Xux8MZaSmIvX8SdQpPiHRccBdxKEL9RM4Z7AzSV7Za61zk46bYnoNTYU= 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=J6BVWd3d; arc=none smtp.client-ip=192.198.163.15 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="J6BVWd3d" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1730740580; x=1762276580; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=Eb5XXjTzfvQ6tkw5JWsvQ0JvCQR7aIn4XD4N0WEQGnM=; b=J6BVWd3d9qxYHhtghuG9y7S/WNGp4nGi+XnbWOdk4A5lER6aJrTfGHmj AmHTfummj53Qc/kZ9RO6jg0o/YZqHt5lhSWAf2OKJvu7ks1VNwQtoIE0H +N2/7tV0dPZoPNMd213W11Fh4v5/GHYJ/yFpDCDRLdYF1vNpKdDs9nGXg aVh2puwCPnAmzbJb8FxAkiAXdBCqafoQqmQtly8/7kZFs2pP2f5x7Akn+ Mj2xRBodGTTYLUDnr78k7U6cwjQ3wktTroQlXPBgxSiFinw4jOw7ljAG3 2wWdSJ4h0bWPlmgtcIzLnP9+guYUirgA+2sg7SrhjRQlXYYN4w+OWJfUQ w==; X-CSE-ConnectionGUID: U/ro7CwkQLu4YO1mEGpXIw== X-CSE-MsgGUID: ZB/YvJaGT/+HFOUspCzEDw== X-IronPort-AV: E=McAfee;i="6700,10204,11246"; a="30563382" X-IronPort-AV: E=Sophos;i="6.11,257,1725346800"; d="scan'208";a="30563382" Received: from fmviesa005.fm.intel.com ([10.60.135.145]) by fmvoesa109.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Nov 2024 09:16:18 -0800 X-CSE-ConnectionGUID: HWdxBvLwQS2nc4s0P4In6Q== X-CSE-MsgGUID: 9X4ec15LSfi8IuUH+5NUAg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.11,257,1725346800"; d="scan'208";a="88230387" Received: from tfalcon-desk.amr.corp.intel.com (HELO [10.124.221.97]) ([10.124.221.97]) by fmviesa005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Nov 2024 09:16:17 -0800 Message-ID: <92dfb8cc-f6eb-4753-950b-944cc26e379f@intel.com> Date: Mon, 4 Nov 2024 09:16:16 -0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v3 1/2] x86: Perform BPF exception fixup in do_user_addr_fault To: Kumar Kartikeya Dwivedi , bpf@vger.kernel.org Cc: kkd@meta.com, Puranjay Mohan , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , Alexander Shishkin , "Kirill A. Shutemov" , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Rishabh Iyer , Sanidhya Kashyap , x86@kernel.org, kernel-team@fb.com References: <20241103193512.4076710-1-memxor@gmail.com> <20241103193512.4076710-2-memxor@gmail.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: <20241103193512.4076710-2-memxor@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/3/24 11:35, Kumar Kartikeya Dwivedi wrote: > Currently, on x86, when SMAP is enabled, and a page fault occurs in > kernel mode for accessing a user address, the kernel will rightly panic > as no valid kernel code can cause such a page fault (unless buggy). > There is no valid correct kernel code that can generate such a fault, > therefore this behavior would be correct. > > BPF programs that currently encounter user addresses when doing > PROBE_MEM loads (load instructions which are allowed to read any kernel > address, only available for root users) avoid a page fault by performing > bounds checking on the address. This requires the JIT to emit a jump > over each PROBE_MEM load instruction to avoid hitting page faults. To be honest, I think the overhead (and complexity) is in the right spot today: the BPF program. I don't want to complicate the x86 page fault handler for a debugging feature that already has a functional solution today.