[PATCHv2] arm: Update all mm structures with section adjustments

[Kees Cook]

On Wed, Nov 18, 2015 at 4:14 PM, Laura Abbott <labbott at fedoraproject.org> wrote:
> Currently, when updating section permissions to mark areas RO
> or NX, the only mm updated is current->mm. This is working off
> the assumption that there are no additional mm structures at
> the time. This may not always hold true. (Example: calling
> modprobe early will trigger a fork/exec). Ensure all mm structres
> get updated with the new section information.
>
> Signed-off-by: Laura Abbott <labbott at fedoraproject.org>

This looks right to me. :)

Reviewed-by: Kees Cook <keescook at chromium.org>

Russell, does this work for you?

-Kees

> ---
> I don't think we can get away from updating the sections if the initmem is
> going to be freed back to the buddy allocator. I think this should cover
> everything based on my understanding but my knowledge may be incomplete.
> ---
>  arch/arm/mm/init.c | 92 ++++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 62 insertions(+), 30 deletions(-)
>
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 8a63b4c..7f8cd1b 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -22,6 +22,7 @@
>  #include <linux/memblock.h>
>  #include <linux/dma-contiguous.h>
>  #include <linux/sizes.h>
> +#include <linux/stop_machine.h>
>
>  #include <asm/cp15.h>
>  #include <asm/mach-types.h>
> @@ -627,12 +628,10 @@ static struct section_perm ro_perms[] = {
>   * safe to be called with preemption disabled, as under stop_machine().
>   */
>  static inline void section_update(unsigned long addr, pmdval_t mask,
> -                                 pmdval_t prot)
> +                                 pmdval_t prot, struct mm_struct *mm)
>  {
> -       struct mm_struct *mm;
>         pmd_t *pmd;
>
> -       mm = current->active_mm;
>         pmd = pmd_offset(pud_offset(pgd_offset(mm, addr), addr), addr);
>
>  #ifdef CONFIG_ARM_LPAE
> @@ -656,49 +655,82 @@ static inline bool arch_has_strict_perms(void)
>         return !!(get_cr() & CR_XP);
>  }
>
> -#define set_section_perms(perms, field)        {                               \
> -       size_t i;                                                       \
> -       unsigned long addr;                                             \
> -                                                                       \
> -       if (!arch_has_strict_perms())                                   \
> -               return;                                                 \
> -                                                                       \
> -       for (i = 0; i < ARRAY_SIZE(perms); i++) {                       \
> -               if (!IS_ALIGNED(perms[i].start, SECTION_SIZE) ||        \
> -                   !IS_ALIGNED(perms[i].end, SECTION_SIZE)) {          \
> -                       pr_err("BUG: section %lx-%lx not aligned to %lx\n", \
> -                               perms[i].start, perms[i].end,           \
> -                               SECTION_SIZE);                          \
> -                       continue;                                       \
> -               }                                                       \
> -                                                                       \
> -               for (addr = perms[i].start;                             \
> -                    addr < perms[i].end;                               \
> -                    addr += SECTION_SIZE)                              \
> -                       section_update(addr, perms[i].mask,             \
> -                                      perms[i].field);                 \
> -       }                                                               \
> +void set_section_perms(struct section_perm *perms, int n, bool set,
> +                       struct mm_struct *mm)
> +{
> +       size_t i;
> +       unsigned long addr;
> +
> +       if (!arch_has_strict_perms())
> +               return;
> +
> +       for (i = 0; i < n; i++) {
> +               if (!IS_ALIGNED(perms[i].start, SECTION_SIZE) ||
> +                   !IS_ALIGNED(perms[i].end, SECTION_SIZE)) {
> +                       pr_err("BUG: section %lx-%lx not aligned to %lx\n",
> +                               perms[i].start, perms[i].end,
> +                               SECTION_SIZE);
> +                       continue;
> +               }
> +
> +               for (addr = perms[i].start;
> +                    addr < perms[i].end;
> +                    addr += SECTION_SIZE)
> +                       section_update(addr, perms[i].mask,
> +                               set ? perms[i].prot : perms[i].clear, mm);
> +       }
> +
>  }
>
> -static inline void fix_kernmem_perms(void)
> +static void update_sections_early(struct section_perm perms[], int n)
>  {
> -       set_section_perms(nx_perms, prot);
> +       struct task_struct *t, *s;
> +
> +       read_lock(&tasklist_lock);
> +       for_each_process(t) {
> +               if (t->flags & PF_KTHREAD)
> +                       continue;
> +               for_each_thread(t, s)
> +                       set_section_perms(perms, n, true, s->mm);
> +       }
> +       read_unlock(&tasklist_lock);
> +       set_section_perms(perms, n, true, current->active_mm);
> +       set_section_perms(perms, n, true, &init_mm);
> +}
> +
> +int __fix_kernmem_perms(void *unused)
> +{
> +       update_sections_early(nx_perms, ARRAY_SIZE(nx_perms));
> +       return 0;
> +}
> +
> +void fix_kernmem_perms(void)
> +{
> +       stop_machine(__fix_kernmem_perms, NULL, NULL);
>  }
>
>  #ifdef CONFIG_DEBUG_RODATA
> +int __mark_rodata_ro(void *unused)
> +{
> +       update_sections_early(ro_perms, ARRAY_SIZE(ro_perms));
> +       return 0;
> +}
> +
>  void mark_rodata_ro(void)
>  {
> -       set_section_perms(ro_perms, prot);
> +       stop_machine(__mark_rodata_ro, NULL, NULL);
>  }
>
>  void set_kernel_text_rw(void)
>  {
> -       set_section_perms(ro_perms, clear);
> +       set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), false,
> +                               current->active_mm);
>  }
>
>  void set_kernel_text_ro(void)
>  {
> -       set_section_perms(ro_perms, prot);
> +       set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), true,
> +                               current->active_mm);
>  }
>  #endif /* CONFIG_DEBUG_RODATA */
>
> --
> 2.5.0
>



-- 
Kees Cook
Chrome OS Security