powerpc/sysfs: Disable writing to PURR in guest mode

arch/powerpc/kernel/sysfs.c exports PURR with write permission.
This may be valid for kernel in phyp mode. But writing to
the file in guest mode causes crash due to a priviledge violation

Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: <stable@vger.kernel.org>

1 files changed, 16 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index 27a90b99ef67..b4e667663d9b 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -17,6 +17,7 @@
 #include <asm/machdep.h>
 #include <asm/smp.h>
 #include <asm/pmc.h>
+#include <asm/firmware.h>
 
 #include "cacheinfo.h"
 
@@ -179,15 +180,25 @@ SYSFS_PMCSETUP(spurr, SPRN_SPURR);
 SYSFS_PMCSETUP(dscr, SPRN_DSCR);
 SYSFS_PMCSETUP(pir, SPRN_PIR);
 
+/*
+  Lets only enable read for phyp resources and
+  enable write when needed with a separate function.
+  Lets be conservative and default to pseries.
+*/
 static DEVICE_ATTR(mmcra, 0600, show_mmcra, store_mmcra);
 static DEVICE_ATTR(spurr, 0400, show_spurr, NULL);
 static DEVICE_ATTR(dscr, 0600, show_dscr, store_dscr);
-static DEVICE_ATTR(purr, 0600, show_purr, store_purr);
+static DEVICE_ATTR(purr, 0400, show_purr, store_purr);
 static DEVICE_ATTR(pir, 0400, show_pir, NULL);
 
 unsigned long dscr_default = 0;
 EXPORT_SYMBOL(dscr_default);
 
+static void add_write_permission_dev_attr(struct device_attribute *attr)
+{
+        attr->attr.mode |= 0200;
+}
+
 static ssize_t show_dscr_default(struct device *dev,
                 struct device_attribute *attr, char *buf)
 {
@@ -394,8 +405,11 @@ static void register_cpu_online(unsigned int cpu)
         if (cpu_has_feature(CPU_FTR_MMCRA))
                 device_create_file(s, &dev_attr_mmcra);
 
-        if (cpu_has_feature(CPU_FTR_PURR))
+        if (cpu_has_feature(CPU_FTR_PURR)) {
+                if (!firmware_has_feature(FW_FEATURE_LPAR))
+                        add_write_permission_dev_attr(&dev_attr_purr);
                 device_create_file(s, &dev_attr_purr);
+        }
 
         if (cpu_has_feature(CPU_FTR_SPURR))
                 device_create_file(s, &dev_attr_spurr);