queue-4.9/0046-x86-speculation-Enable-prctl-mode-for-spectre_v2_use.patch

   1 From 83c1822ea048f5429d8cc0ba7f662978c500db85 Mon Sep 17 00:00:00 2001
   2 From: Thomas Gleixner <tglx@linutronix.de>
   3 Date: Sun, 25 Nov 2018 19:33:54 +0100
   4 Subject: [PATCH 46/76] x86/speculation: Enable prctl mode for spectre_v2_user
   5
   6 commit 7cc765a67d8e04ef7d772425ca5a2a1e2b894c15 upstream.
   7
   8 Now that all prerequisites are in place:
   9
  10  - Add the prctl command line option
  11
  12  - Default the 'auto' mode to 'prctl'
  13
  14  - When SMT state changes, update the static key which controls the
  15    conditional STIBP evaluation on context switch.
  16
  17  - At init update the static key which controls the conditional IBPB
  18    evaluation on context switch.
  19
  20 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  21 Reviewed-by: Ingo Molnar <mingo@kernel.org>
  22 Cc: Peter Zijlstra <peterz@infradead.org>
  23 Cc: Andy Lutomirski <luto@kernel.org>
  24 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  25 Cc: Jiri Kosina <jkosina@suse.cz>
  26 Cc: Tom Lendacky <thomas.lendacky@amd.com>
  27 Cc: Josh Poimboeuf <jpoimboe@redhat.com>
  28 Cc: Andrea Arcangeli <aarcange@redhat.com>
  29 Cc: David Woodhouse <dwmw@amazon.co.uk>
  30 Cc: Tim Chen <tim.c.chen@linux.intel.com>
  31 Cc: Andi Kleen <ak@linux.intel.com>
  32 Cc: Dave Hansen <dave.hansen@intel.com>
  33 Cc: Casey Schaufler <casey.schaufler@intel.com>
  34 Cc: Asit Mallick <asit.k.mallick@intel.com>
  35 Cc: Arjan van de Ven <arjan@linux.intel.com>
  36 Cc: Jon Masters <jcm@redhat.com>
  37 Cc: Waiman Long <longman9394@gmail.com>
  38 Cc: Greg KH <gregkh@linuxfoundation.org>
  39 Cc: Dave Stewart <david.c.stewart@intel.com>
  40 Cc: Kees Cook <keescook@chromium.org>
  41 Link: https://lkml.kernel.org/r/20181125185005.958421388@linutronix.de
  42 [bwh: Backported to 4.9: adjust filename]
  43 Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
  44 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  45 ---
  46  Documentation/kernel-parameters.txt |  7 ++++-
  47  arch/x86/kernel/cpu/bugs.c          | 41 ++++++++++++++++++++++-------
  48  2 files changed, 38 insertions(+), 10 deletions(-)
  49
  50 diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
  51 index cef2cb9cbf8a..f87e4bf2ab25 100644
  52 --- a/Documentation/kernel-parameters.txt
  53 +++ b/Documentation/kernel-parameters.txt
  54 @@ -4075,9 +4075,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
  55                         off     - Unconditionally disable mitigations. Is
  56                                   enforced by spectre_v2=off
  57
  58 +                       prctl   - Indirect branch speculation is enabled,
  59 +                                 but mitigation can be enabled via prctl
  60 +                                 per thread.  The mitigation control state
  61 +                                 is inherited on fork.
  62 +
  63                         auto    - Kernel selects the mitigation depending on
  64                                   the available CPU features and vulnerability.
  65 -                                 Default is off.
  66 +                                 Default is prctl.
  67
  68                         Not specifying this option is equivalent to
  69                         spectre_v2_user=auto.
  70 diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
  71 index 3308f18a637d..e28598f3ab12 100644
  72 --- a/arch/x86/kernel/cpu/bugs.c
  73 +++ b/arch/x86/kernel/cpu/bugs.c
  74 @@ -253,11 +253,13 @@ enum spectre_v2_user_cmd {
  75         SPECTRE_V2_USER_CMD_NONE,
  76         SPECTRE_V2_USER_CMD_AUTO,
  77         SPECTRE_V2_USER_CMD_FORCE,
  78 +       SPECTRE_V2_USER_CMD_PRCTL,
  79  };
  80
  81  static const char * const spectre_v2_user_strings[] = {
  82         [SPECTRE_V2_USER_NONE]          = "User space: Vulnerable",
  83         [SPECTRE_V2_USER_STRICT]        = "User space: Mitigation: STIBP protection",
  84 +       [SPECTRE_V2_USER_PRCTL]         = "User space: Mitigation: STIBP via prctl",
  85  };
  86
  87  static const struct {
  88 @@ -268,6 +270,7 @@ static const struct {
  89         { "auto",       SPECTRE_V2_USER_CMD_AUTO,       false },
  90         { "off",        SPECTRE_V2_USER_CMD_NONE,       false },
  91         { "on",         SPECTRE_V2_USER_CMD_FORCE,      true  },
  92 +       { "prctl",      SPECTRE_V2_USER_CMD_PRCTL,      false },
  93  };
  94
  95  static void __init spec_v2_user_print_cond(const char *reason, bool secure)
  96 @@ -322,12 +325,15 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
  97                 smt_possible = false;
  98
  99         switch (spectre_v2_parse_user_cmdline(v2_cmd)) {
 100 -       case SPECTRE_V2_USER_CMD_AUTO:
 101         case SPECTRE_V2_USER_CMD_NONE:
 102                 goto set_mode;
 103         case SPECTRE_V2_USER_CMD_FORCE:
 104                 mode = SPECTRE_V2_USER_STRICT;
 105                 break;
 106 +       case SPECTRE_V2_USER_CMD_AUTO:
 107 +       case SPECTRE_V2_USER_CMD_PRCTL:
 108 +               mode = SPECTRE_V2_USER_PRCTL;
 109 +               break;
 110         }
 111
 112         /* Initialize Indirect Branch Prediction Barrier */
 113 @@ -338,6 +344,9 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
 114                 case SPECTRE_V2_USER_STRICT:
 115                         static_branch_enable(&switch_mm_always_ibpb);
 116                         break;
 117 +               case SPECTRE_V2_USER_PRCTL:
 118 +                       static_branch_enable(&switch_mm_cond_ibpb);
 119 +                       break;
 120                 default:
 121                         break;
 122                 }
 123 @@ -350,6 +359,12 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
 124         if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
 125                 return;
 126
 127 +       /*
 128 +        * If SMT is not possible or STIBP is not available clear the STIPB
 129 +        * mode.
 130 +        */
 131 +       if (!smt_possible || !boot_cpu_has(X86_FEATURE_STIBP))
 132 +               mode = SPECTRE_V2_USER_NONE;
 133  set_mode:
 134         spectre_v2_user = mode;
 135         /* Only print the STIBP mode when SMT possible */
 136 @@ -557,6 +572,15 @@ static void update_stibp_strict(void)
 137         on_each_cpu(update_stibp_msr, NULL, 1);
 138  }
 139
 140 +/* Update the static key controlling the evaluation of TIF_SPEC_IB */
 141 +static void update_indir_branch_cond(void)
 142 +{
 143 +       if (sched_smt_active())
 144 +               static_branch_enable(&switch_to_cond_stibp);
 145 +       else
 146 +               static_branch_disable(&switch_to_cond_stibp);
 147 +}
 148 +
 149  void arch_smt_update(void)
 150  {
 151         /* Enhanced IBRS implies STIBP. No update required. */
 152 @@ -572,6 +596,7 @@ void arch_smt_update(void)
 153                 update_stibp_strict();
 154                 break;
 155         case SPECTRE_V2_USER_PRCTL:
 156 +               update_indir_branch_cond();
 157                 break;
 158         }
 159
 160 @@ -1044,7 +1069,8 @@ static char *stibp_state(void)
 161         case SPECTRE_V2_USER_STRICT:
 162                 return ", STIBP: forced";
 163         case SPECTRE_V2_USER_PRCTL:
 164 -               return "";
 165 +               if (static_key_enabled(&switch_to_cond_stibp))
 166 +                       return ", STIBP: conditional";
 167         }
 168         return "";
 169  }
 170 @@ -1052,14 +1078,11 @@ static char *stibp_state(void)
 171  static char *ibpb_state(void)
 172  {
 173         if (boot_cpu_has(X86_FEATURE_IBPB)) {
 174 -               switch (spectre_v2_user) {
 175 -               case SPECTRE_V2_USER_NONE:
 176 -                       return ", IBPB: disabled";
 177 -               case SPECTRE_V2_USER_STRICT:
 178 +               if (static_key_enabled(&switch_mm_always_ibpb))
 179                         return ", IBPB: always-on";
 180 -               case SPECTRE_V2_USER_PRCTL:
 181 -                       return "";
 182 -               }
 183 +               if (static_key_enabled(&switch_mm_cond_ibpb))
 184 +                       return ", IBPB: conditional";
 185 +               return ", IBPB: disabled";
 186         }
 187         return "";
 188  }
 189 --
 190 2.21.0
 191