linux-kernel - Re: [PATCH v3 5/5] platform/x86: think-lmi: mutex protection around multiple WMI calls

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Date:   Mon, 29 May 2023 15:23:42 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Mark Pearson <mpearson-lenovo@...ebb.ca>
cc:     hdegoede@...hat.com, markgross@...nel.org,
        platform-driver-x86@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 5/5] platform/x86: think-lmi: mutex protection around
 multiple WMI calls

On Fri, 26 May 2023, Mark Pearson wrote:

> Add mutex protection around cases where an operation needs multiple
> WMI calls - e.g. setting password.

So you need this feature already for Patch 1/5? If that's the case, you 
should reorder the patches and put it before 1/5.

That "e.g. setting password" sounds vague enough that I'm left to wonder 
if there are other cases in the driver which need locking too. It would be 
useful to be precise with wording here. It will help immensely when 
somebody looks this changelog 5 years from now if you explain all cases 
that need locking up front.

So, is this needed also for some existing code, then Fixes tag might be in 
order? (I'm looking e.g. that cert auth block in current_value_store() 
which also does more than one call).

-- 
 i.

> Signed-off-by: Mark Pearson <mpearson-lenovo@...ebb.ca>
> ---
> Changes in v2: New commit added after review of other patches in series.
> Changes in v3: Simplified mutex handling as recommended.
> 
>  drivers/platform/x86/think-lmi.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/x86/think-lmi.c b/drivers/platform/x86/think-lmi.c
> index 64cd453d6e7d..86185358dba2 100644
> --- a/drivers/platform/x86/think-lmi.c
> +++ b/drivers/platform/x86/think-lmi.c
> @@ -14,6 +14,7 @@
>  #include <linux/acpi.h>
>  #include <linux/errno.h>
>  #include <linux/fs.h>
> +#include <linux/mutex.h>
>  #include <linux/string.h>
>  #include <linux/types.h>
>  #include <linux/dmi.h>
> @@ -195,6 +196,7 @@ static const char * const level_options[] = {
>  };
>  static struct think_lmi tlmi_priv;
>  static struct class *fw_attr_class;
> +static DEFINE_MUTEX(tlmi_mutex);
>  
>  /* ------ Utility functions ------------*/
>  /* Strip out CR if one is present */
> @@ -437,6 +439,9 @@ static ssize_t new_password_store(struct kobject *kobj,
>  	/* Strip out CR if one is present, setting password won't work if it is present */
>  	strip_cr(new_pwd);
>  
> +	/* Use lock in case multiple WMI operations needed */
> +	mutex_lock(&tlmi_mutex);
> +
>  	pwdlen = strlen(new_pwd);
>  	/* pwdlen == 0 is allowed to clear the password */
>  	if (pwdlen && ((pwdlen < setting->minlen) || (pwdlen > setting->maxlen))) {
> @@ -493,6 +498,7 @@ static ssize_t new_password_store(struct kobject *kobj,
>  		kfree(auth_str);
>  	}
>  out:
> +	mutex_unlock(&tlmi_mutex);
>  	kfree(new_pwd);
>  	return ret ?: count;
>  }
> @@ -987,6 +993,9 @@ static ssize_t current_value_store(struct kobject *kobj,
>  	/* Strip out CR if one is present */
>  	strip_cr(new_setting);
>  
> +	/* Use lock in case multiple WMI operations needed */
> +	mutex_lock(&tlmi_mutex);
> +
>  	/* Check if certificate authentication is enabled and active */
>  	if (tlmi_priv.certificate_support && tlmi_priv.pwd_admin->cert_installed) {
>  		if (!tlmi_priv.pwd_admin->signature || !tlmi_priv.pwd_admin->save_signature) {
> @@ -1031,7 +1040,6 @@ static ssize_t current_value_store(struct kobject *kobj,
>  			if (ret)
>  				goto out;
>  		}
> -
>  		ret = tlmi_save_bios_settings("");
>  	} else { /* old non opcode based authentication method (deprecated)*/
>  		if (tlmi_priv.pwd_admin->valid && tlmi_priv.pwd_admin->password[0]) {
> @@ -1071,6 +1079,7 @@ static ssize_t current_value_store(struct kobject *kobj,
>  		kobject_uevent(&tlmi_priv.class_dev->kobj, KOBJ_CHANGE);
>  	}
>  out:
> +	mutex_unlock(&tlmi_mutex);
>  	kfree(auth_str);
>  	kfree(set_str);
>  	kfree(new_setting);
>