[PATCH v2] powerpc/papr_scm: Limit the readability of 'perf_stats' sysfs attribute

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 updates access mode of 'perf_stats' attribute to
be only readable by root users.

Fixes: 2d02bf835e573 ('powerpc/papr_scm: Fetch nvdimm performance stats from PHYP')
Reported-by: Aneesh Kumar K.V <redacted>
Signed-off-by: Vaibhav Jain <redacted>
---
Change-log:

v2:
* Instead of checking for perfmon_capable() inside show_perf_stats()
  set the attribute as DEVICE_ATTR_ADMIN_RO [ Aneesh ]
* Update patch description
---
 arch/powerpc/platforms/pseries/papr_scm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index f439f0dfea7d1..a88a707a608aa 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c

@@ -822,7 +822,7 @@ static ssize_t perf_stats_show(struct device *dev,
 	kfree(stats);
 	return rc ? rc : seq_buf_used(&s);
 }
-DEVICE_ATTR_RO(perf_stats);
+DEVICE_ATTR_ADMIN_RO(perf_stats);
 
 static ssize_t flags_show(struct device *dev,
 			  struct device_attribute *attr, char *buf)

-- 
2.26.2

On Mon, Sep 07, 2020 at 04:35:40PM +0530, 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

	                                   ^^^
                                           off?

from users who don't need to access these performance statistics.

Hence this patch updates access mode of 'perf_stats' attribute to
be only readable by root users.

Generally it is bad form to say "this patch".  See 4c here:

	-- https://www.ozlabs.org/~akpm/stuff/tpp.txt

But I'm not picky...  :-D

With the s/of/off/ change:

Reviewed-by: Ira Weiny <redacted>

On Mon, 7 Sep 2020 16:35:40 +0530, 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.

[...]

Applied to powerpc/fixes.

[1/1] powerpc/papr_scm: Limit the readability of 'perf_stats' sysfs attribute
      https://git.kernel.org/powerpc/c/0460534b532e5518c657c7d6492b9337d975eaa3

cheers