This is a note to let you know that I've just added the patch titled
x86/MCE: Serialize sysfs changes
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-mce-serialize-sysfs-changes.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From b3b7c4795ccab5be71f080774c45bbbcc75c2aaf Mon Sep 17 00:00:00 2001
From: Seunghun Han <kkamagui@xxxxxxxxx>
Date: Tue, 6 Mar 2018 15:21:43 +0100
Subject: x86/MCE: Serialize sysfs changes
From: Seunghun Han <kkamagui@xxxxxxxxx>
commit b3b7c4795ccab5be71f080774c45bbbcc75c2aaf upstream.
The check_interval file in
/sys/devices/system/machinecheck/machinecheck<cpu number>
directory is a global timer value for MCE polling. If it is changed by one
CPU, mce_restart() broadcasts the event to other CPUs to delete and restart
the MCE polling timer and __mcheck_cpu_init_timer() reinitializes the
mce_timer variable.
If more than one CPU writes a specific value to the check_interval file
concurrently, mce_timer is not protected from such concurrent accesses and
all kinds of explosions happen. Since only root can write to those sysfs
variables, the issue is not a big deal security-wise.
However, concurrent writes to these configuration variables is void of
reason so the proper thing to do is to serialize the access with a mutex.
Boris:
- Make store_int_with_restart() use device_store_ulong() to filter out
negative intervals
- Limit min interval to 1 second
- Correct locking
- Massage commit message
Signed-off-by: Seunghun Han <kkamagui@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: linux-edac <linux-edac@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20180302202706.9434-1-kkamagui@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/mcheck/mce.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -61,6 +61,9 @@ static DEFINE_MUTEX(mce_chrdev_read_mute
smp_load_acquire(&(p)); \
})
+/* sysfs synchronization */
+static DEFINE_MUTEX(mce_sysfs_mutex);
+
#define CREATE_TRACE_POINTS
#include <trace/events/mce.h>
@@ -2308,6 +2311,7 @@ static ssize_t set_ignore_ce(struct devi
if (kstrtou64(buf, 0, &new) < 0)
return -EINVAL;
+ mutex_lock(&mce_sysfs_mutex);
if (mca_cfg.ignore_ce ^ !!new) {
if (new) {
/* disable ce features */
@@ -2320,6 +2324,8 @@ static ssize_t set_ignore_ce(struct devi
on_each_cpu(mce_enable_ce, (void *)1, 1);
}
}
+ mutex_unlock(&mce_sysfs_mutex);
+
return size;
}
@@ -2332,6 +2338,7 @@ static ssize_t set_cmci_disabled(struct
if (kstrtou64(buf, 0, &new) < 0)
return -EINVAL;
+ mutex_lock(&mce_sysfs_mutex);
if (mca_cfg.cmci_disabled ^ !!new) {
if (new) {
/* disable cmci */
@@ -2343,6 +2350,8 @@ static ssize_t set_cmci_disabled(struct
on_each_cpu(mce_enable_ce, NULL, 1);
}
}
+ mutex_unlock(&mce_sysfs_mutex);
+
return size;
}
@@ -2350,8 +2359,19 @@ static ssize_t store_int_with_restart(st
struct device_attribute *attr,
const char *buf, size_t size)
{
- ssize_t ret = device_store_int(s, attr, buf, size);
+ unsigned long old_check_interval = check_interval;
+ ssize_t ret = device_store_ulong(s, attr, buf, size);
+
+ if (check_interval == old_check_interval)
+ return ret;
+
+ if (check_interval < 1)
+ check_interval = 1;
+
+ mutex_lock(&mce_sysfs_mutex);
mce_restart();
+ mutex_unlock(&mce_sysfs_mutex);
+
return ret;
}
Patches currently in stable-queue which might be from kkamagui@xxxxxxxxx are
queue-4.9/x86-mce-serialize-sysfs-changes.patch