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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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