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    SubjectRe: [kernel-hardening] Re: [PATCH 2/2] arm: apply more __ro_after_init
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    On Wed, 2016-08-10 at 10:43 +0100, Russell King - ARM Linux wrote:
    > On Fri, Jun 03, 2016 at 11:40:24AM -0700, Kees Cook wrote:
    > >
    > > @@ -1309,16 +1309,11 @@ void __init arm_mm_memblock_reserve(void)
    > >   * Any other function or debugging method which may touch any
    > > device _will_
    > >   * crash the kernel.
    > >   */
    > > +static char vectors[PAGE_SIZE * 2] __ro_after_init
    > > __aligned(PAGE_SIZE);
    > >  static void __init devicemaps_init(const struct machine_desc
    > > *mdesc)
    > >  {
    > >   struct map_desc map;
    > >   unsigned long addr;
    > > - void *vectors;
    > > -
    > > - /*
    > > -  * Allocate the vector page early.
    > > -  */
    > > - vectors = early_alloc(PAGE_SIZE * 2);
    >
    > This one is not appropriate.  We _do_ write to these pages after init
    > for FIQ handler updates.  See set_fiq_handler().

    This is one of the many cases where pax_open_kernel/pax_close_kernel are
    needed to temporarily toggle it read-only. From grsecurity:

    @@ -95,7 +95,10 @@ void set_fiq_handler(void *start, unsigned int
    length)
      void *base = vectors_page;
      unsigned offset = FIQ_OFFSET;
     
    + pax_open_kernel();
      memcpy(base + offset, start, length);
    + pax_close_kernel();[unhandled content-type:application/pgp-signature]
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