releases/3.10.32/x86-smap-smap_violation-is-bogus-if-config_x86_smap-is-off.patch

   1 From 4640c7ee9b8953237d05a61ea3ea93981d1bc961 Mon Sep 17 00:00:00 2001
   2 From: "H. Peter Anvin" <hpa@linux.intel.com>
   3 Date: Thu, 13 Feb 2014 07:46:04 -0800
   4 Subject: x86, smap: smap_violation() is bogus if CONFIG_X86_SMAP is off
   5
   6 From: "H. Peter Anvin" <hpa@linux.intel.com>
   7
   8 commit 4640c7ee9b8953237d05a61ea3ea93981d1bc961 upstream.
   9
  10 If CONFIG_X86_SMAP is disabled, smap_violation() tests for conditions
  11 which are incorrect (as the AC flag doesn't matter), causing spurious
  12 faults.
  13
  14 The dynamic disabling of SMAP (nosmap on the command line) is fine
  15 because it disables X86_FEATURE_SMAP, therefore causing the
  16 static_cpu_has() to return false.
  17
  18 Found by Fengguang Wu's test system.
  19
  20 [ v3: move all predicates into smap_violation() ]
  21 [ v2: use IS_ENABLED() instead of #ifdef ]
  22
  23 Reported-by: Fengguang Wu <fengguang.wu@intel.com>
  24 Link: http://lkml.kernel.org/r/20140213124550.GA30497@localhost
  25 Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
  26 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  27
  28 ---
  29  arch/x86/mm/fault.c |   14 +++++++++-----
  30  1 file changed, 9 insertions(+), 5 deletions(-)
  31
  32 --- a/arch/x86/mm/fault.c
  33 +++ b/arch/x86/mm/fault.c
  34 @@ -989,6 +989,12 @@ static int fault_in_kernel_space(unsigne
  35
  36  static inline bool smap_violation(int error_code, struct pt_regs *regs)
  37  {
  38 +       if (!IS_ENABLED(CONFIG_X86_SMAP))
  39 +               return false;
  40 +
  41 +       if (!static_cpu_has(X86_FEATURE_SMAP))
  42 +               return false;
  43 +
  44         if (error_code & PF_USER)
  45                 return false;
  46
  47 @@ -1091,11 +1097,9 @@ __do_page_fault(struct pt_regs *regs, un
  48         if (unlikely(error_code & PF_RSVD))
  49                 pgtable_bad(regs, error_code, address);
  50
  51 -       if (static_cpu_has(X86_FEATURE_SMAP)) {
  52 -               if (unlikely(smap_violation(error_code, regs))) {
  53 -                       bad_area_nosemaphore(regs, error_code, address);
  54 -                       return;
  55 -               }
  56 +       if (unlikely(smap_violation(error_code, regs))) {
  57 +               bad_area_nosemaphore(regs, error_code, address);
  58 +               return;
  59         }
  60
  61         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);