[PATCH 3.4 44/44] powerpc/sysfs: Disable writing to PURR in guest mode

Greg Kroah-Hartman
2014-07-08T00:03:47Z

From: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>

commit d1211af3049f4c9c1d8d4eb8f8098cc4f4f0d0c7 upstream.

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>
[Backported to 3.4: adjust context]
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/kernel/sysfs.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

--- 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, 0600, 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 __cpuinit register_cpu_onlin
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);