[PATCH] powerpc/papr_scm: Limit the readability of 'perf_stats' sysfs attribute

[Aneesh Kumar K.V]

On 8/13/20 10:04 AM, Vaibhav Jain wrote:
> The newly introduced 'perf_stats' attribute uses the default access
> mode of 0444 letting non-root users access performance stats of an
> nvdimm and potentially force the kernel into issuing large number of
> expensive HCALLs. Since the information exposed by this attribute
> cannot be cached hence its better to ward of access to this attribute
> from users who don't need to access these performance statistics.
> 
> Hence this patch adds check in perf_stats_show() to only let users
> that are 'perfmon_capable()' to read the nvdimm performance
> statistics.
> 
> Fixes: 2d02bf835e573 ('powerpc/papr_scm: Fetch nvdimm performance stats from PHYP')
> Reported-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
> Signed-off-by: Vaibhav Jain <vaibhav at linux.ibm.com>
> ---
>   arch/powerpc/platforms/pseries/papr_scm.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index f439f0dfea7d1..36c51bf8af9a8 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -792,6 +792,10 @@ static ssize_t perf_stats_show(struct device *dev,
>   	struct nvdimm *dimm = to_nvdimm(dev);
>   	struct papr_scm_priv *p = nvdimm_provider_data(dimm);
>   
> +	/* Allow access only to perfmon capable users */
> +	if (!perfmon_capable())
> +		return -EACCES;
> +

An access check is usually done in open(). This is the read callback IIUC.

>   	if (!p->stat_buffer_len)
>   		return -ENOENT;
>   
> 

-aneesh