[PATCH][v2] Enable CONFIG_STRICT_DEVMEM support for Powerpc

[Sukadev Bhattiprolu]

>From aebed2e9fb9fba7dd0a34595780b828d7a545ba2 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
Date: Mon, 29 Aug 2011 14:12:08 -0700
Subject: [PATCH 1/1][v2] Enable CONFIG_STRICT_DEVMEM support for Powerpc.

As described in the help text in the patch, this token restricts general
access to /dev/mem as a way of increasing 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 POWER. 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.

A test for this patch:

	# cat /proc/rtas/rmo_buffer 
	000000000f190000 10000

	# python -c "print 0x000000000f190000 / 0x10000"
	3865

	# dd if=/dev/mem of=/tmp/foo count=1 bs=64k skip=3865
	1+0 records in
	1+0 records out
	65536 bytes (66 kB) copied, 0.000205235 s, 319 MB/s

	# dd if=/dev/mem of=/tmp/foo count=1 bs=64k skip=3864
	dd: reading `/dev/mem': Operation not permitted
	0+0 records in
	0+0 records out
	0 bytes (0 B) copied, 0.000226844 s, 0.0 kB/s

	# dd if=/dev/mem of=/tmp/foo count=1 bs=64k skip=3866
	dd: reading `/dev/mem': Operation not permitted
	0+0 records in
	0+0 records out
	0 bytes (0 B) copied, 0.00023542 s, 0.0 kB/s

	# dd if=/dev/mem of=/tmp/foo
	dd: reading `/dev/mem': Operation not permitted
	0+0 records in
	0+0 records out
	0 bytes (0 B) copied, 0.00022519 s, 0.0 kB/s

Changelog[v2]:
	- [Anton Blanchard] Punch a hole in devmem to allow librtas/dlpar
	  tools access to /dev/mem.

Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
---
 arch/powerpc/Kconfig.debug      |   12 ++++++++++++
 arch/powerpc/include/asm/page.h |    1 +
 arch/powerpc/kernel/rtas.c      |   10 ++++++++++
 arch/powerpc/mm/mem.c           |   20 ++++++++++++++++++++
 drivers/char/mem.c              |    5 +++--
 5 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 067cb84..1cf1b00 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -298,4 +298,16 @@ config PPC_EARLY_DEBUG_CPM_ADDR
 	  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
diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
index 2cd664e..dc2ec96 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -261,6 +261,7 @@ extern void clear_user_page(void *page, unsigned long vaddr, struct page *pg);
 extern void copy_user_page(void *to, void *from, unsigned long vaddr,
 		struct page *p);
 extern int page_is_ram(unsigned long pfn);
+extern int devmem_is_allowed(unsigned long pfn);
 
 #ifdef CONFIG_PPC_SMLPAR
 void arch_free_page(struct page *page, int order);
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index d5ca823..07cf2cf 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -937,6 +937,16 @@ asmlinkage int ppc_rtas(struct rtas_args __user *uargs)
 	return 0;
 }
 
+int page_is_rtas(unsigned long pfn)
+{
+	unsigned long paddr = (pfn << PAGE_SHIFT);
+
+	if (paddr >= rtas_rmo_buf && paddr < (rtas_rmo_buf + RTAS_RMOBUF_MAX))
+		return 1;
+
+	return 0;
+}
+
 /*
  * Call early during boot, before mem init or bootmem, to retrieve the RTAS
  * informations from the device-tree and allocate the RMO buffer for userland
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index c781bbc..d21dbc6 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -549,3 +549,23 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 	hash_preload(vma->vm_mm, address, access, trap);
 #endif /* CONFIG_PPC_STD_MMU */
 }
+
+extern int page_is_rtas(unsigned long pfn);
+
+/*
+ * devmem_is_allowed(): check to see if /dev/mem access to a certain address
+ * is valid. The argument is a physical page number.
+ *
+ * Access has to be given to non-kernel-ram areas as well, these contain the
+ * PCI mmio resources as well as potential bios/acpi data regions.
+ */
+int devmem_is_allowed(unsigned long pfn)
+{
+	if (iomem_is_exclusive(pfn << PAGE_SHIFT))
+		return 0;
+	if (!page_is_ram(pfn))
+		return 1;
+	if (page_is_rtas(pfn))
+		return 1;
+	return 0;
+}
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 8fc04b4..64917e8 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -29,6 +29,7 @@
 
 #include <asm/uaccess.h>
 #include <asm/io.h>
+#include <asm/page.h>
 
 #ifdef CONFIG_IA64
 # include <linux/efi.h>
@@ -66,8 +67,8 @@ static inline int range_is_allowed(unsigned long pfn, unsigned long size)
 	while (cursor < to) {
 		if (!devmem_is_allowed(pfn)) {
 			printk(KERN_INFO
-		"Program %s tried to access /dev/mem between %Lx->%Lx.\n",
-				current->comm, from, to);
+		"Program %s tried to access /dev/mem between %Lx->%Lx and "
+			"pfn %lu.\n", current->comm, from, to, pfn);
 			return 0;
 		}
 		cursor += PAGE_SIZE;
-- 
1.7.0.4