x86/mm: Implement ASLR for hugetlb mappings

Matthew noticed that hugetlb mappings don't participate in ASLR on x86-64:

  %  for i in `seq 3`; do
  > tools/testing/selftests/vm/map_hugetlb | grep address
  > done
  Returned address is 0x2aaaaac00000
  Returned address is 0x2aaaaac00000
  Returned address is 0x2aaaaac00000

/proc/PID/maps entries for the mapping are always the same
(except inode number):

  2aaaaac00000-2aaabac00000 rw-p 00000000 00:0c 8200              /anon_hugepage (deleted)
  2aaaaac00000-2aaabac00000 rw-p 00000000 00:0c 256               /anon_hugepage (deleted)
  2aaaaac00000-2aaabac00000 rw-p 00000000 00:0c 7180              /anon_hugepage (deleted)

The reason is the generic hugetlb_get_unmapped_area() function
which is used on x86-64.  It doesn't support randomization and
use bottom-up unmapped area lookup, instead of usual top-down
on x86-64.

x86 has arch-specific hugetlb_get_unmapped_area(), but it's used
only on x86-32.

Let's use arch-specific hugetlb_get_unmapped_area() on x86-64
too. That adds ASLR and switches hugetlb mappings to use top-down
unmapped area lookup:

  %  for i in `seq 3`; do
  > tools/testing/selftests/vm/map_hugetlb | grep address
  > done
  Returned address is 0x7f4f08a00000
  Returned address is 0x7fdda4200000
  Returned address is 0x7febe0000000

/proc/PID/maps entries:

  7f4f08a00000-7f4f18a00000 rw-p 00000000 00:0c 1168              /anon_hugepage (deleted)
  7fdda4200000-7fddb4200000 rw-p 00000000 00:0c 7092              /anon_hugepage (deleted)
  7febe0000000-7febf0000000 rw-p 00000000 00:0c 7183              /anon_hugepage (deleted)

Unmapped area lookup policy for hugetlb mappings is consistent
with normal mappings now -- the only difference is alignment
requirements for huge pages.

libhugetlbfs test-suite didn't detect any regressions with the
patch applied (although it shows few failures on my machine
regardless the patch).

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/r/20131119131750.EA45CE0090@blue.fi.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index 9d980d88b747..8c9f647ff9e1 100644
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -87,9 +87,7 @@ int pmd_huge_support(void)
 }
 #endif
 
-/* x86_64 also uses this file */
-
-#ifdef HAVE_ARCH_HUGETLB_UNMAPPED_AREA
+#ifdef CONFIG_HUGETLB_PAGE
 static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
                 unsigned long addr, unsigned long len,
                 unsigned long pgoff, unsigned long flags)
@@ -99,7 +97,7 @@ static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
 
         info.flags = 0;
         info.length = len;
-        info.low_limit = TASK_UNMAPPED_BASE;
+        info.low_limit = current->mm->mmap_legacy_base;
         info.high_limit = TASK_SIZE;
         info.align_mask = PAGE_MASK & ~huge_page_mask(h);
         info.align_offset = 0;
@@ -172,8 +170,7 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
                 return hugetlb_get_unmapped_area_topdown(file, addr, len,
                                 pgoff, flags);
 }
-
-#endif /*HAVE_ARCH_HUGETLB_UNMAPPED_AREA*/
+#endif /* CONFIG_HUGETLB_PAGE */
 
 #ifdef CONFIG_X86_64
 static __init int setup_hugepagesz(char *opt)