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SubjectRe: Linux 5.3-rc8
On Thu, Sep 12, 2019 at 04:25:30AM -0400, Theodore Y. Ts'o wrote:
> On Thu, Sep 12, 2019 at 05:44:21AM +0200, Ahmed S. Darwish wrote:
[...]
>
> > 1. Cutting down the number of bits needed to initialize the CRNG
> > to 256 bits (CHACHA20 cipher)
>
> Does the attach patch (see below) help?
>
[...]
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 5d5ea4ce1442..b9b3a5a82abf 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -500,7 +500,7 @@ static int crng_init = 0;
> #define crng_ready() (likely(crng_init > 1))
> static int crng_init_cnt = 0;
> static unsigned long crng_global_init_time = 0;
> -#define CRNG_INIT_CNT_THRESH (2*CHACHA_KEY_SIZE)
> +#define CRNG_INIT_CNT_THRESH CHACHA_KEY_SIZE
> static void _extract_crng(struct crng_state *crng, __u8 out[CHACHA_BLOCK_SIZE]);
> static void _crng_backtrack_protect(struct crng_state *crng,
> __u8 tmp[CHACHA_BLOCK_SIZE], int used);

Unfortunately, it only made the early fast init faster, but didn't fix
the normal crng init blockage :-(

Here's a trace log, got by applying the patch at [1]. The boot was
continued only after typing some random keys after ~30s:

#
# entries-in-buffer/entries-written: 22/22 #P:8
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
<idle>-0 [001] dNh. 0.687088: crng_fast_load: crng threshold = 32
<idle>-0 [001] dNh. 0.687089: crng_fast_load: crng_init_cnt = 0
<idle>-0 [001] dNh. 0.687090: crng_fast_load: crng_init_cnt, now set to 16
<idle>-0 [001] dNh. 0.705208: crng_fast_load: crng threshold = 32
<idle>-0 [001] dNh. 0.705209: crng_fast_load: crng_init_cnt = 16
<idle>-0 [001] dNh. 0.705209: crng_fast_load: crng_init_cnt, now set to 32
<idle>-0 [001] dNh. 0.708048: crng_fast_load: random: fast init done
lvm-165 [001] d... 2.417971: urandom_read: random: crng_init_cnt, now set to 0
systemd-random--179 [003] .... 2.495669: wait_for_random_bytes.part.0: wait for randomness
dbus-daemon-274 [006] dN.. 3.294331: urandom_read: random: crng_init_cnt, now set to 0
dbus-daemon-274 [006] dN.. 3.316618: urandom_read: random: crng_init_cnt, now set to 0
polkitd-286 [007] dN.. 3.873918: urandom_read: random: crng_init_cnt, now set to 0
polkitd-286 [007] dN.. 3.874303: urandom_read: random: crng_init_cnt, now set to 0
polkitd-286 [007] dN.. 3.874375: urandom_read: random: crng_init_cnt, now set to 0
polkitd-286 [007] d... 3.886204: urandom_read: random: crng_init_cnt, now set to 0
polkitd-286 [007] d... 3.886217: urandom_read: random: crng_init_cnt, now set to 0
polkitd-286 [007] d... 3.888519: urandom_read: random: crng_init_cnt, now set to 0
polkitd-286 [007] d... 3.888529: urandom_read: random: crng_init_cnt, now set to 0
gnome-session-b-321 [006] .... 4.292034: wait_for_random_bytes.part.0: wait for randomness
<idle>-0 [002] dNh. 36.784001: crng_reseed: random: crng init done
gnome-session-b-321 [006] .... 36.784019: wait_for_random_bytes.part.0: wait done
systemd-random--179 [003] .... 36.784051: wait_for_random_bytes.part.0: wait done

[1] patch:

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 5d5ea4ce1442..4a50ee2c230d 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -500,7 +500,7 @@ static int crng_init = 0;
#define crng_ready() (likely(crng_init > 1))
static int crng_init_cnt = 0;
static unsigned long crng_global_init_time = 0;
-#define CRNG_INIT_CNT_THRESH (2*CHACHA_KEY_SIZE)
+#define CRNG_INIT_CNT_THRESH (CHACHA_KEY_SIZE)
static void _extract_crng(struct crng_state *crng, __u8 out[CHACHA_BLOCK_SIZE]);
static void _crng_backtrack_protect(struct crng_state *crng,
__u8 tmp[CHACHA_BLOCK_SIZE], int used);
@@ -931,6 +931,9 @@ static int crng_fast_load(const char *cp, size_t len)
unsigned long flags;
char *p;

+ trace_printk("crng threshold = %d\n", CRNG_INIT_CNT_THRESH);
+ trace_printk("crng_init_cnt = %d\n", crng_init_cnt);
+
if (!spin_trylock_irqsave(&primary_crng.lock, flags))
return 0;
if (crng_init != 0) {
@@ -943,11 +946,15 @@ static int crng_fast_load(const char *cp, size_t len)
cp++; crng_init_cnt++; len--;
}
spin_unlock_irqrestore(&primary_crng.lock, flags);
+
+ trace_printk("crng_init_cnt, now set to %d\n", crng_init_cnt);
+
if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
invalidate_batched_entropy();
crng_init = 1;
wake_up_interruptible(&crng_init_wait);
pr_notice("random: fast init done\n");
+ trace_printk("random: fast init done\n");
}
return 1;
}
@@ -1033,6 +1040,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);
pr_notice("random: crng init done\n");
+ trace_printk("random: crng init done\n");
if (unseeded_warning.missed) {
pr_notice("random: %d get_random_xx warning(s) missed "
"due to ratelimiting\n",
@@ -1743,9 +1751,16 @@ EXPORT_SYMBOL(get_random_bytes);
*/
int wait_for_random_bytes(void)
{
+ int ret;
+
if (likely(crng_ready()))
return 0;
- return wait_event_interruptible(crng_init_wait, crng_ready());
+
+ trace_printk("wait for randomness\n");
+ ret = wait_event_interruptible(crng_init_wait, crng_ready());
+ trace_printk("wait done\n");
+
+ return ret;
}
EXPORT_SYMBOL(wait_for_random_bytes);

@@ -1974,6 +1989,8 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
current->comm, nbytes);
spin_lock_irqsave(&primary_crng.lock, flags);
crng_init_cnt = 0;
+ trace_printk("random: crng_init_cnt, now set to %d\n",
+ crng_init_cnt);
spin_unlock_irqrestore(&primary_crng.lock, flags);
}
nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));
thanks,

--
darwi
http://darwish.chasingpointers.com

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