From e00d996a4317aff5351c4338dd97d390225412c2 Mon Sep 17 00:00:00 2001
From: Qian Cai <cai@lca.pw>
Date: Tue, 25 Feb 2020 11:27:04 -0500
Subject: [PATCH] random: fix data races at timer_rand_state
Git-commit: e00d996a4317aff5351c4338dd97d390225412c2
Patch-mainline: v5.7-rc1
References: bsc#1173438
Fields in "struct timer_rand_state" could be accessed concurrently.
Lockless plain reads and writes result in data races. Fix them by adding
pairs of READ|WRITE_ONCE(). The data races were reported by KCSAN,
BUG: KCSAN: data-race in add_timer_randomness / add_timer_randomness
write to 0xffff9f320a0a01d0 of 8 bytes by interrupt on cpu 22:
add_timer_randomness+0x100/0x190
add_timer_randomness at drivers/char/random.c:1152
add_disk_randomness+0x85/0x280
scsi_end_request+0x43a/0x4a0
scsi_io_completion+0xb7/0x7e0
scsi_finish_command+0x1ed/0x2a0
scsi_softirq_done+0x1c9/0x1d0
blk_done_softirq+0x181/0x1d0
__do_softirq+0xd9/0x57c
irq_exit+0xa2/0xc0
do_IRQ+0x8b/0x190
ret_from_intr+0x0/0x42
cpuidle_enter_state+0x15e/0x980
cpuidle_enter+0x69/0xc0
call_cpuidle+0x23/0x40
do_idle+0x248/0x280
cpu_startup_entry+0x1d/0x1f
start_secondary+0x1b2/0x230
secondary_startup_64+0xb6/0xc0
no locks held by swapper/22/0.
irq event stamp: 32871382
_raw_spin_unlock_irqrestore+0x53/0x60
_raw_spin_lock_irqsave+0x21/0x60
_local_bh_enable+0x21/0x30
irq_exit+0xa2/0xc0
read to 0xffff9f320a0a01d0 of 8 bytes by interrupt on cpu 2:
add_timer_randomness+0xe8/0x190
add_disk_randomness+0x85/0x280
scsi_end_request+0x43a/0x4a0
scsi_io_completion+0xb7/0x7e0
scsi_finish_command+0x1ed/0x2a0
scsi_softirq_done+0x1c9/0x1d0
blk_done_softirq+0x181/0x1d0
__do_softirq+0xd9/0x57c
irq_exit+0xa2/0xc0
do_IRQ+0x8b/0x190
ret_from_intr+0x0/0x42
cpuidle_enter_state+0x15e/0x980
cpuidle_enter+0x69/0xc0
call_cpuidle+0x23/0x40
do_idle+0x248/0x280
cpu_startup_entry+0x1d/0x1f
start_secondary+0x1b2/0x230
secondary_startup_64+0xb6/0xc0
no locks held by swapper/2/0.
irq event stamp: 37846304
_raw_spin_unlock_irqrestore+0x53/0x60
_raw_spin_lock_irqsave+0x21/0x60
_local_bh_enable+0x21/0x30
irq_exit+0xa2/0xc0
Reported by Kernel Concurrency Sanitizer on:
Hardware name: HP ProLiant BL660c Gen9, BIOS I38 10/17/2018
Link: https://lore.kernel.org/r/1582648024-13111-1-git-send-email-cai@lca.pw
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
drivers/char/random.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index c33e7a3cdb13..f43f65c2195d 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1170,14 +1170,14 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
* We take into account the first, second and third-order deltas
* in order to make our estimate.
*/
- delta = sample.jiffies - state->last_time;
- state->last_time = sample.jiffies;
+ delta = sample.jiffies - READ_ONCE(state->last_time);
+ WRITE_ONCE(state->last_time, sample.jiffies);
- delta2 = delta - state->last_delta;
- state->last_delta = delta;
+ delta2 = delta - READ_ONCE(state->last_delta);
+ WRITE_ONCE(state->last_delta, delta);
- delta3 = delta2 - state->last_delta2;
- state->last_delta2 = delta2;
+ delta3 = delta2 - READ_ONCE(state->last_delta2);
+ WRITE_ONCE(state->last_delta2, delta2);
if (delta < 0)
delta = -delta;
--
2.26.2