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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: <20190204155535.GC9802@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: b6dc7839-ea71-422f-4192-08d68ab93536 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: DM5PR01MB3210 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Feb 03, 2019 at 08:09:37AM -0500, Prarit Bhargava wrote: > Ted, the bug I'm trying to fix is the warning: > > random: get_random_bytes called from start_kernel+0x8e/0x587 with crng_init=0 > > during early boot. Even with the kernel parameter the warning appears. Sometimes the warnings are real, and shouldn't be suppressed. A Debian maintainer once tried to suppress a compile-time warning, and it was disastrous for security. :-) What line number is that corresponding to? It sounds like something is trying to use get_random_bytes() before the random driver was initialized, and so the first question is does it really need to call get_random_bytes() then or can it be moved? > > Also, relying on the TSC for entropy is not something we should be > > recommending. > > The current code uses the TSC. It is not something new I'm introducing. But we don't *rely* on it. That's a big difference. - Ted