From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from outgoing.mit.edu (outgoing-auth-1.mit.edu [18.9.28.11]) (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 B99842208F for ; Sat, 3 Feb 2024 14:36:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=18.9.28.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706970991; cv=none; b=GQbbWm6EEGSAHFa1VX/SAgoF38fjyxIF9Qf/xqPicK06OER/dVXVenA/UmC29tSgG9099RxtOAQ02soPMlnaCuPvSLQFOMm/VAfHFsoc7Ezm/llGfucqvUl89mwg12HWqOEHrd4RrWQl76ojAoG8KTTpwD9Qp3MvG1mfUMBunRI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706970991; c=relaxed/simple; bh=5zVRnjyDndBGcBDaYKnA/6ke/KUEwTKEduciNLtEb20=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ehDNmJTo3DqB/FAjT16kBLBTE3VtpxDqjYSDE6H0UULJGWU8xNGKn4ToCtM30MrwEpbb7j+qmiYDBPiatkFVX7Nz9AWkfcraHBZLC+WTvcQnpfIbWC7kwQR5HsKYJsvMcgWZ7tLe9JeWbCzWZXcxji+hINZe2bSJOS2WxVPPyTU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=mit.edu; spf=pass smtp.mailfrom=mit.edu; dkim=pass (2048-bit key) header.d=mit.edu header.i=@mit.edu header.b=YYN4u85c; arc=none smtp.client-ip=18.9.28.11 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=mit.edu Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mit.edu Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mit.edu header.i=@mit.edu header.b="YYN4u85c" Received: from cwcc.thunk.org (pool-173-48-82-236.bstnma.fios.verizon.net [173.48.82.236]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 413EZl0m014620 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sat, 3 Feb 2024 09:35:48 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mit.edu; s=outgoing; t=1706970953; bh=W9QRnEoj1oim8rFp3GQ1Wc3cLjSRInO2QO0PatD71QY=; h=Date:From:Subject:Message-ID:MIME-Version:Content-Type; b=YYN4u85clNWA8JLLCI02AQorfr9PBNeSBudlXfEAghMoEz0ZTBX7ghOZdHIcOLzER sso4j0KZjG5omETRiKLSrvvArg1CpQdW2ZKYU70F/1fp0It9dsx+x1eYjohjvHk+nf 406gLLSAJ5fqnLdQ1gcAXvLTYBNF9SjoTKDI8WNOxTCktL/Onfows6h/+K6AcFK08V ZYvbJ/8duGPRC2fjNpSO9okEUmqeh8fSquvfsUZ+VDk243VZuek02iZIlznCVtdQS7 xZDoCTyPpPoEfN2tP5um/biKDEPB4YKgDbbh1C4dH1GPafv2aU4xzocVoRJQDCKITn i/su3IuLPf62g== Received: by cwcc.thunk.org (Postfix, from userid 15806) id 3ED9915C02FC; Sat, 3 Feb 2024 09:35:47 -0500 (EST) Date: Sat, 3 Feb 2024 09:35:47 -0500 From: "Theodore Ts'o" To: James Bottomley Cc: "Jason A. Donenfeld" , "Reshetova, Elena" , 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" Subject: Re: [PATCH 1/2] x86/random: Retry on RDSEED failure Message-ID: <20240203143547.GC36616@mit.edu> References: <20240131140756.GB2356784@mit.edu> <20240131171042.GA2371371@mit.edu> <20240201045710.GD2356784@mit.edu> <20240202160515.GC119530@mit.edu> <6ccd8c7998542f1ac68514700fb9e31049a3a3c7.camel@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6ccd8c7998542f1ac68514700fb9e31049a3a3c7.camel@linux.ibm.com> On Fri, Feb 02, 2024 at 10:28:01PM +0100, James Bottomley wrote: > > My big concern is older cpus where rdrand/rdseed don't produce useful > entropy. Exhaustion attacks are going to be largely against VMs not > physical systems, so I worry about physical systems with older CPUs > that might have rdrand issues which then trip our Confidential > Computing checks. For (non-CC) VM's the answer is virtio-rng. This solves the exhaustion problem, since if you can't trust the host, the VM's security is taost anyway (again, ignoring Confidential Compute). > The signal for rdseed failing is fairly clear, so if the node has other > entropy sources, it should continue otherwise it should signal failure. > Figuring out how a confidential computing environment signals that > failure is TBD. That's a design decision, and I believe we've been converging on a panic during early boot. Post boot, if we've successfully succeeded in initializing the guest kernel's RNG, we're secure so long as the cryptographic primitives haven't been defeated --- and if we have, such as if Quantuum Computing because practical, we've got bigger problems anyway. - Ted