powerpc: Implement CONFIG_STRICT_DEVMEM
As described in the help text in the patch, this token restricts general
access to /dev/mem as a way of increasing the security. Specifically, access
to exclusive IOMEM and kernel RAM is denied unless CONFIG_STRICT_DEVMEM is
set to 'n'.
Implement the 'devmem_is_allowed()' interface for Powerpc. It will be
called from range_is_allowed() when userpsace attempts to access /dev/mem.
This patch is based on an earlier patch from Steve Best and with input from
Paul Mackerras and Scott Wood.
[BenH] Fixed a typo or two and removed the generic change which should
be submitted as a separate patch
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 1b8a9c9..4ccb2a0 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -336,4 +336,16 @@
platform probing is done, all platforms selected must
share the same address.
+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.
+
endmenu
