This is a note to let you know that I've just added the patch titled

x86/MCE: Serialize sysfs changes

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-mce-serialize-sysfs-changes.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From b3b7c4795ccab5be71f080774c45bbbcc75c2aaf Mon Sep 17 00:00:00 2001

From: Seunghun Han kkamagui@gmail.com Date: Tue, 6 Mar 2018 15:21:43 +0100 Subject: x86/MCE: Serialize sysfs changes

From: Seunghun Han kkamagui@gmail.com

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@gmail.com Signed-off-by: Borislav Petkov bp@suse.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Tony Luck tony.luck@intel.com Cc: linux-edac linux-edac@vger.kernel.org Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20180302202706.9434-1-kkamagui@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- 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 @@ -57,6 +57,9 @@

static DEFINE_MUTEX(mce_log_mutex);

+/* sysfs synchronization */ +static DEFINE_MUTEX(mce_sysfs_mutex); + #define CREATE_TRACE_POINTS #include <trace/events/mce.h>

@@ -2080,6 +2083,7 @@ 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 */ @@ -2092,6 +2096,8 @@ static ssize_t set_ignore_ce(struct devi on_each_cpu(mce_enable_ce, (void *)1, 1); } } + mutex_unlock(&mce_sysfs_mutex); + return size; }

@@ -2104,6 +2110,7 @@ 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 */ @@ -2115,6 +2122,8 @@ static ssize_t set_cmci_disabled(struct on_each_cpu(mce_enable_ce, NULL, 1); } } + mutex_unlock(&mce_sysfs_mutex); + return size; }

@@ -2122,8 +2131,19 @@ 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@gmail.com are

queue-4.15/x86-mce-serialize-sysfs-changes.patch