linux-kernel - Re: [PATCH] hwmon: (xgene) restrict power measurements to admin by default

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Date:   Fri, 3 Jun 2022 08:37:04 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     D Scott Phillips <scott@...amperecomputing.com>,
        linux-hwmon@...r.kernel.org
Cc:     Jean Delvare <jdelvare@...e.com>, linux-kernel@...r.kernel.org,
        patches@...erecomputing.com,
        Darren Hart <darren@...amperecomputing.com>,
        Ilkka Koskinen <ilkka@...amperecomputing.com>
Subject: Re: [PATCH] hwmon: (xgene) restrict power measurements to admin by
 default

On 6/3/22 08:21, D Scott Phillips wrote:
> Access to power information can be used to infer the instructions being run
> and possibly even data being processed on a cpu[1]. Restrict access to
> power information to administrator users by default. (Cf. a similar
> powercap change[2].)
> 
> [1]: Lipp, Moritz, et al. "PLATYPUS: software-based power side-channel
>       attacks on x86." 2021 IEEE Symposium on Security and Privacy (SP).
>       IEEE, 2021.
> [2]: commit 949dd0104c49 ("powercap: restrict energy meter to root access")
> 
> Fixes: ed42cfa881e1 ("hwmon: Add xgene hwmon driver")
> Signed-off-by: D Scott Phillips <scott@...amperecomputing.com>
> Cc: stable@...r.kernel.org
> ---
>   drivers/hwmon/xgene-hwmon.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/xgene-hwmon.c b/drivers/hwmon/xgene-hwmon.c
> index 5cde837bfd09..6ad1daf2d354 100644
> --- a/drivers/hwmon/xgene-hwmon.c
> +++ b/drivers/hwmon/xgene-hwmon.c
> @@ -397,9 +397,9 @@ static DEVICE_ATTR_RO(temp1_label);
>   static DEVICE_ATTR_RO(temp1_input);
>   static DEVICE_ATTR_RO(temp1_critical_alarm);
>   static DEVICE_ATTR_RO(power1_label);
> -static DEVICE_ATTR_RO(power1_input);
> +static DEVICE_ATTR_ADMIN_RO(power1_input);
>   static DEVICE_ATTR_RO(power2_label);
> -static DEVICE_ATTR_RO(power2_input);
> +static DEVICE_ATTR_ADMIN_RO(power2_input);
>   
>   static struct attribute *xgene_hwmon_attrs[] = {
>   	&dev_attr_temp1_label.attr,


NACK. The hwmon ABI expects world read access. Either find a workaround
by making the measurements less accurate, or drop the driver. Also see
commit 9049572fb145 ("hwmon: Remove amd_energy driver"), "Attribute access"
in Documentation/hwmon/sysfs-interface.rst, and [1].

Guenter


---
[1] https://patchwork.kernel.org/project/linux-hwmon/patch/20210409174852.4585-2-linux@roeck-us.net/