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Subject[PATCH] NOMMU: add support for Memory Protection Units (MPU)
Date
From: Bernd Schmidt <bernds_cb1@t-online.de>

Some architectures (like the Blackfin arch) implement some of the
"simpler" features that one would expect out of a MMU such as memory
protection. In our case, we actually get read/write/exec protection
down to the page boundary so processes can't stomp on each other let
alone the kernel. There is a performance decrease (which depends greatly
on the workload) however as the hardware/software interaction was not
optimized at design time.

Signed-off-by: Bernd Schmidt <bernds_cb1@t-online.de>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
CC: David Howells <dhowells@redhat.com>
---
kernel/module.c | 5 +++++
mm/nommu.c | 25 +++++++++++++++++++++++++
2 files changed, 30 insertions(+), 0 deletions(-)
diff --git a/kernel/module.c b/kernel/module.c
index 0a04983..e1a3dfc 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -47,6 +47,7 @@
#include <linux/rculist.h>
#include <asm/uaccess.h>
#include <asm/cacheflush.h>
+#include <asm/mmu_context.h>
#include <linux/license.h>
#include <asm/sections.h>
#include <linux/tracepoint.h>
@@ -1519,6 +1520,10 @@ static void free_module(struct module *mod)

/* Finally, free the core (containing the module structure) */
module_free(mod, mod->module_core);
+
+#ifdef CONFIG_MPU
+ update_protections(current->mm);
+#endif
}

void *__symbol_get(const char *symbol)
diff --git a/mm/nommu.c b/mm/nommu.c
index 53cab10..a0269e5 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -33,6 +33,7 @@
#include <asm/uaccess.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>
+#include <asm/mmu_context.h>
#include "internal.h"

static inline __attribute__((format(printf, 1, 2)))
@@ -640,11 +641,23 @@ static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
struct vm_area_struct *pvma, **pp;
struct address_space *mapping;
struct rb_node **p, *parent;
+#ifdef CONFIG_MPU
+ long start;
+#endif

kenter(",%p", vma);

BUG_ON(!vma->vm_region);

+#ifdef CONFIG_MPU
+ start = vma->vm_start & PAGE_MASK;
+ while (start < vma->vm_end) {
+ protect_page(mm, start, vma->vm_flags);
+ start += PAGE_SIZE;
+ }
+ update_protections(mm);
+#endif
+
mm->map_count++;
vma->vm_mm = mm;

@@ -707,9 +720,21 @@ static void delete_vma_from_mm(struct vm_area_struct *vma)
struct vm_area_struct **pp;
struct address_space *mapping;
struct mm_struct *mm = vma->vm_mm;
+#ifdef CONFIG_MPU
+ long start;
+#endif

kenter("%p", vma);

+#ifdef CONFIG_MPU
+ start = vma->vm_start & PAGE_MASK;
+ while (start < vma->vm_end) {
+ protect_page(mm, start, 0);
+ start += PAGE_SIZE;
+ }
+ update_protections(mm);
+#endif
+
mm->map_count--;
if (mm->mmap_cache == vma)
mm->mmap_cache = NULL;
--
1.6.3.3


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