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Ts'o" To: Prarit Bhargava CC: , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , , Arnd Bergmann , Greg Kroah-Hartman , Rik van Riel , Andrew Morton , Philippe Ombredanne , Kees Cook , "Jason A. Donenfeld" , Kate Stewart Subject: Re: [PATCH v2] x86, random: Fix get_random_bytes() warning in x86 start_kernel Message-ID: <20190202030240.GA9802@mit.edu> Mail-Followup-To: "Theodore Y. Ts'o" , Prarit Bhargava , linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Arnd Bergmann , Greg Kroah-Hartman , Rik van Riel , Andrew Morton , Philippe Ombredanne , Kees Cook , "Jason A. 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X-MS-Exchange-CrossTenant-Network-Message-Id: d49b47c8-9f9e-4967-658f-08d688bae80a X-MS-Exchange-CrossTenant-Id: 64afd9ba-0ecf-4acf-bc36-935f6235ba8b X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=64afd9ba-0ecf-4acf-bc36-935f6235ba8b;Ip=[18.9.28.11];Helo=[outgoing.mit.edu] X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN7PR01MB3745 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 01, 2019 at 01:08:31PM -0500, Prarit Bhargava wrote: > After 43838a23a05f ("random: fix crng_ready() test") early boot calls to > get_random_bytes() will warn on x86 because the crng is not initialized. > For example, > > random: get_random_bytes called from start_kernel+0x8e/0x587 with crng_init=0 > > x86 only uses get_random_bytes() for better randomization of the stack > canary value so the warning is of no consequence. > > Test if the crng is initialized before calling get_random_bytes(). If it > is not available then attempt to read from the hardware random generator, > before finally using the TSC. If you want to trust the CPU's hardware number generator, there is a way to do this already. Simply enable CONFIG_RANDOM_TRUST_CPU, or set the boot command line option "random.trust_cpu=on". Also, relying on the TSC for entropy is not something we should be recommending. So, NAK. - Ted