From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.20]) (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 3818913DB9F for ; Wed, 14 Feb 2024 20:14:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.20 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707941690; cv=none; b=O88UQFijEcFBkIb+KFVPpKcMG2HUOvmc3XnwgTOyq+xsAHFz66eQMF/jvvwPKZVadMEtUSL8K1S6FTJXVb1Xc5bAkcCBCLqV0AP1qxkYUQVgSa3LIooLk5QBkyGK1zql9S2wb2jnRBooCFZozvvHYjhULkNqDskikiufUQ27C8I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707941690; c=relaxed/simple; bh=d6+qwRXP6NphmHa1ubVYOWYhwIVVKde9de8ktr2i2DI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Z0zxS6z7i+aQb20oxe+LuHvLG1QXiRSavAJr4zSi7t8w2j7ShSDCDKQ71kSM6gwk4GFhrhHsDfzxFcOyCsawf0N1dcnXYjm5ftkFjudJZo9VxgfiS7vyEzZkuErxqlPEW/cAhMOJe7cFHoWKsxJWnee4wDkXKqxmzVLL8EW0YmE= 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=KL9CGCpl; arc=none smtp.client-ip=198.175.65.20 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="KL9CGCpl" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1707941688; x=1739477688; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=d6+qwRXP6NphmHa1ubVYOWYhwIVVKde9de8ktr2i2DI=; b=KL9CGCpls/S88FV5gCxkReNGkWCvx719ueWuoCJYdOi6KSZKtUBZ7uFT oDdPOi9PVt/mMnSmZVd2tXlJrTOH1ct33FhjtAnCcTnNdxHEZ+1e/1NuX /L5pjfB86V+Y7TVDJj5/Ce/mhdxApG1/1z3LFkeUNrCligKW+LkI2x7Dt bpi8WncT70OnzQk1vBASPyFqBQ1L/FUfVB84wfFvT+7wp2n/GaTZ0Fzf6 d1L6G/SqelWw+XlbLBwBu41Pp5tYw6rIeNQhc3xlWVs2JXlwL2sLKfS8q ndJUddug3ecDZEt+QwDxHTvDtMjPJOeaIPabKnjYmZzviyULnDILKK/dd w==; X-IronPort-AV: E=McAfee;i="6600,9927,10984"; a="1880703" X-IronPort-AV: E=Sophos;i="6.06,160,1705392000"; d="scan'208";a="1880703" Received: from orviesa007.jf.intel.com ([10.64.159.147]) by orvoesa112.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Feb 2024 12:14:47 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.06,160,1705392000"; d="scan'208";a="3625907" Received: from lshoer-mobl1.amr.corp.intel.com (HELO [10.209.111.90]) ([10.209.111.90]) by orviesa007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Feb 2024 12:14:47 -0800 Message-ID: Date: Wed, 14 Feb 2024 12:14:46 -0800 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 1/2] x86/random: Retry on RDSEED failure Content-Language: en-US To: "Jason A. Donenfeld" , "Reshetova, Elena" Cc: Theodore Ts'o , Dave Hansen , "Kirill A. Shutemov" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , "x86@kernel.org" , Kuppuswamy Sathyanarayanan , "Nakajima, Jun" , Tom Lendacky , "Kalra, Ashish" , Sean Christopherson , "linux-coco@lists.linux.dev" , "linux-kernel@vger.kernel.org" References: <20240131140756.GB2356784@mit.edu> <20240131171042.GA2371371@mit.edu> <20240201045710.GD2356784@mit.edu> From: Dave Hansen 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/14/24 09:21, Jason A. Donenfeld wrote: > One clarifying question in all of this: what is the point of the "try 10 > times" advice? Is the "faster than the bus" statement actually "faster > than the bus if you try 10 times"? Or is the "10 times" advice just old > and not relevant. > > In other words, is the following a reasonable patch? > > diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h > index 02bae8e0758b..2d5bf5aa9774 100644 > --- a/arch/x86/include/asm/archrandom.h > +++ b/arch/x86/include/asm/archrandom.h > @@ -13,22 +13,16 @@ > #include > #include > > -#define RDRAND_RETRY_LOOPS 10 > - > /* Unconditional execution of RDRAND and RDSEED */ > > static inline bool __must_check rdrand_long(unsigned long *v) > { > bool ok; > - unsigned int retry = RDRAND_RETRY_LOOPS; > - do { > - asm volatile("rdrand %[out]" > - CC_SET(c) > - : CC_OUT(c) (ok), [out] "=r" (*v)); > - if (ok) > - return true; > - } while (--retry); > - return false; > + asm volatile("rdrand %[out]" > + CC_SET(c) > + : CC_OUT(c) (ok), [out] "=r" (*v)); > + WARN_ON(!ok); > + return ok; > } The key question here is if RDRAND can ever fail on perfectly good hardware. I think it's theoretically possible for the entropy source health checks to fail on perfectly good hardware for an arbitrarily long time. But the odds of this happening to the point of it affecting RDRAND are rather small. There's a reason that the guidance says: "the odds of ten failures in a row are astronomically small" _instead_ of claiming the same about a single RDRAND. Given the scale that the kernel operates at, I think we should leave the loop.