[PATCH 2/2] arm: apply more __ro_after_init

On Wed, Aug 10, 2016 at 12:00:53PM +0200, Arnd Bergmann wrote:

On Wednesday, August 10, 2016 10:43:39 AM CEST Russell King - ARM Linux wrote:

quoted

On Fri, Jun 03, 2016 at 11:40:24AM -0700, Kees Cook wrote:

quoted

@@ -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().

Is that the only thing that modifies the page? If we think this is a
valuable change, we could make it depend on the absence of FIQ
support, as very few platforms (rpc, omap1, s3c24xx and possibly
imx) seem to even use it.

There's the TLS emulation too, but that writes via the vectors mapping
at 0xffff0ff0.

-- 
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