[S390] mm: add devmem_is_allowed() for STRICT_DEVMEM checking

Provide the devmem_is_allowed() routine to restrict access to
kernel memory from userspace.
Set the CONFIG_STRICT_DEVMEM config option to switch on checking.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/s390/Kconfig.debug b/arch/s390/Kconfig.debug
index 45e0c6199f3..05221b13ffb 100644
--- a/arch/s390/Kconfig.debug
+++ b/arch/s390/Kconfig.debug
@@ -6,6 +6,18 @@ config TRACE_IRQFLAGS_SUPPORT
 
 source "lib/Kconfig.debug"
 
+config STRICT_DEVMEM
+        def_bool y
+        prompt "Filter access to /dev/mem"
+        ---help---
+          This option restricts access to /dev/mem.  If this option is
+          disabled, you allow userspace access to all memory, including
+          kernel and userspace memory. Accidental memory access is likely
+          to be disastrous.
+          Memory access is required for experts who want to debug the kernel.
+
+          If you are unsure, say Y.
+
 config DEBUG_STRICT_USER_COPY_CHECKS
         bool "Strict user copy size checks"
         ---help---