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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Theodore Tso <tytso@mit.edu>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>
Subject: [PATCH 4.9 040/264] random: move rand_initialize() earlier
Date:   Thu, 23 Jun 2022 18:40:33 +0200
Message-Id: <20220623164345.203575295@linuxfoundation.org>
In-Reply-To: <20220623164344.053938039@linuxfoundation.org>
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From: Kees Cook <keescook@chromium.org>

commit d55535232c3dbde9a523a9d10d68670f5fe5dec3 upstream.

Right now rand_initialize() is run as an early_initcall(), but it only
depends on timekeeping_init() (for mixing ktime_get_real() into the
pools). However, the call to boot_init_stack_canary() for stack canary
initialization runs earlier, which triggers a warning at boot:

random: get_random_bytes called from start_kernel+0x357/0x548 with crng_init=0

Instead, this moves rand_initialize() to after timekeeping_init(), and moves
canary initialization here as well.

Note that this warning may still remain for machines that do not have
UEFI RNG support (which initializes the RNG pools during setup_arch()),
or for x86 machines without RDRAND (or booting without "random.trust=on"
or CONFIG_RANDOM_TRUST_CPU=y).

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/char/random.c  |    5 ++---
 include/linux/random.h |    1 +
 init/main.c            |   14 ++++++++++++++
 3 files changed, 17 insertions(+), 3 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1842,7 +1842,7 @@ EXPORT_SYMBOL(get_random_bytes_arch);
  * data into the pool to prepare it for use. The pool is not cleared
  * as that can only decrease the entropy in the pool.
  */
-static void init_std_data(struct entropy_store *r)
+static void __init init_std_data(struct entropy_store *r)
 {
 	int i;
 	ktime_t now = ktime_get_real();
@@ -1869,7 +1869,7 @@ static void init_std_data(struct entropy
  * take care not to overwrite the precious per platform data
  * we were given.
  */
-static int rand_initialize(void)
+int __init rand_initialize(void)
 {
 	init_std_data(&input_pool);
 	init_std_data(&blocking_pool);
@@ -1881,7 +1881,6 @@ static int rand_initialize(void)
 	}
 	return 0;
 }
-early_initcall(rand_initialize);
 
 #ifdef CONFIG_BLOCK
 void rand_initialize_disk(struct gendisk *disk)
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -35,6 +35,7 @@ extern void add_interrupt_randomness(int
 
 extern void get_random_bytes(void *buf, int nbytes);
 extern int wait_for_random_bytes(void);
+extern int __init rand_initialize(void);
 extern bool rng_is_initialized(void);
 extern int add_random_ready_callback(struct random_ready_callback *rdy);
 extern void del_random_ready_callback(struct random_ready_callback *rdy);
--- a/init/main.c
+++ b/init/main.c
@@ -570,6 +570,20 @@ asmlinkage __visible void __init start_k
 	hrtimers_init();
 	softirq_init();
 	timekeeping_init();
+
+	/*
+	 * For best initial stack canary entropy, prepare it after:
+	 * - setup_arch() for any UEFI RNG entropy and boot cmdline access
+	 * - timekeeping_init() for ktime entropy used in rand_initialize()
+	 * - rand_initialize() to get any arch-specific entropy like RDRAND
+	 * - add_latent_entropy() to get any latent entropy
+	 * - adding command line entropy
+	 */
+	rand_initialize();
+	add_latent_entropy();
+	add_device_randomness(command_line, strlen(command_line));
+	boot_init_stack_canary();
+
 	time_init();
 	sched_clock_postinit();
 	printk_nmi_init();