x86: Add RO/NX protection for loadable kernel modules

This patch is a logical extension of the protection provided by
CONFIG_DEBUG_RODATA to LKMs. The protection is provided by
splitting module_core and module_init into three logical parts
each and setting appropriate page access permissions for each
individual section:

 1. Code: RO+X
 2. RO data: RO+NX
 3. RW data: RW+NX

In order to achieve proper protection, layout_sections() have
been modified to align each of the three parts mentioned above
onto page boundary. Next, the corresponding page access
permissions are set right before successful exit from
load_module(). Further, free_module() and sys_init_module have
been modified to set module_core and module_init as RW+NX right
before calling module_free().

By default, the original section layout and access flags are
preserved. When compiled with CONFIG_DEBUG_SET_MODULE_RONX=y,
the patch will page-align each group of sections to ensure that
each page contains only one type of content and will enforce
RO/NX for each group of pages.

  -v1: Initial proof-of-concept patch.
  -v2: The patch have been re-written to reduce the number of #ifdefs
       and to make it architecture-agnostic. Code formatting has also
       been corrected.
  -v3: Opportunistic RO/NX protection is now unconditional. Section
       page-alignment is enabled when CONFIG_DEBUG_RODATA=y.
  -v4: Removed most macros and improved coding style.
  -v5: Changed page-alignment and RO/NX section size calculation
  -v6: Fixed comments. Restricted RO/NX enforcement to x86 only
  -v7: Introduced CONFIG_DEBUG_SET_MODULE_RONX, added
       calls to set_all_modules_text_rw() and set_all_modules_text_ro()
       in ftrace
  -v8: updated for compatibility with linux 2.6.33-rc5
  -v9: coding style fixes
 -v10: more coding style fixes
 -v11: minor adjustments for -tip
 -v12: minor adjustments for v2.6.35-rc2-tip
 -v13: minor adjustments for v2.6.37-rc1-tip

Signed-off-by: Siarhei Liakh <sliakh.lkml@gmail.com>
Signed-off-by: Xuxian Jiang <jiang@cs.ncsu.edu>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Reviewed-by: James Morris <jmorris@namei.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dave Jones <davej@redhat.com>
Cc: Kees Cook <kees.cook@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <4CE2F914.9070106@free.fr>
[ minor cleanliness edits, -v14: build failure fix ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>