linux-kernel - [RFC PATCH 24/41] init: call time_init() before rand

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Date:   Mon, 21 Sep 2020 09:58:40 +0200
From:   Nicolai Stange <nstange@...e.de>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Peter Matthias <matthias.peter@....bund.de>,
        Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        Roman Drahtmueller <draht@...altsekun.de>,
        Neil Horman <nhorman@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Julia Lawall <julia.lawall@...ia.fr>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Andy Lavr <andy.lavr@...il.com>,
        Eric Biggers <ebiggers@...nel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Stephan Müller <smueller@...onox.de>,
        Torsten Duwe <duwe@...e.de>, Petr Tesarik <ptesarik@...e.cz>,
        Nicolai Stange <nstange@...e.de>
Subject: [RFC PATCH 24/41] init: call time_init() before rand_initialize()

Commit d55535232c3d ("random: move rand_initialize() earlier") moved the
rand_initialize() invocation from the early initcalls to right after
timekeeping_init(), but before time_init().

However, rand_initialize() would indirectly invoke random_get_entropy(),
which is an alias to get_cycles() on most archs, in case an architectural
RNG is not available. Problem is that on some archs, e.g. ARM,
get_cycles() can only be relied upon when time_init() has completed.

Move the invocation of time_init() a couple of lines up in start_kernel()
so that it gets called before rand_initialize().

Note that random_get_entropy() data doesn't get any entropy credit and
thus, this issue is not to be considered a bug, but more of an
inconsistency.

Fixes: d55535232c3d ("random: move rand_initialize() earlier")
Signed-off-by: Nicolai Stange <nstange@...e.de>
---
 init/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/init/main.c b/init/main.c
index ae78fb68d231..30892675f48e 100644
--- a/init/main.c
+++ b/init/main.c
@@ -942,6 +942,7 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
 	hrtimers_init();
 	softirq_init();
 	timekeeping_init();
+	time_init();
 
 	/*
 	 * For best initial stack canary entropy, prepare it after:
@@ -956,7 +957,6 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
 	add_device_randomness(command_line, strlen(command_line));
 	boot_init_stack_canary();
 
-	time_init();
 	perf_event_init();
 	profile_init();
 	call_function_init();
-- 
2.26.2