queue-4.9/0026-x86-speculation-Disable-STIBP-when-enhanced-IBRS-is-.patch

   1 From 029e37a0a97ec027d83e657f493d1e618935aa5d Mon Sep 17 00:00:00 2001
   2 From: Tim Chen <tim.c.chen@linux.intel.com>
   3 Date: Sun, 25 Nov 2018 19:33:33 +0100
   4 Subject: [PATCH 26/76] x86/speculation: Disable STIBP when enhanced IBRS is in
   5  use
   6
   7 commit 34bce7c9690b1d897686aac89604ba7adc365556 upstream.
   8
   9 If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2
  10 user space exploits from hyperthread sibling.
  11
  12 Disable STIBP when enhanced IBRS is used.
  13
  14 Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
  15 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  16 Reviewed-by: Ingo Molnar <mingo@kernel.org>
  17 Cc: Peter Zijlstra <peterz@infradead.org>
  18 Cc: Andy Lutomirski <luto@kernel.org>
  19 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  20 Cc: Jiri Kosina <jkosina@suse.cz>
  21 Cc: Tom Lendacky <thomas.lendacky@amd.com>
  22 Cc: Josh Poimboeuf <jpoimboe@redhat.com>
  23 Cc: Andrea Arcangeli <aarcange@redhat.com>
  24 Cc: David Woodhouse <dwmw@amazon.co.uk>
  25 Cc: Andi Kleen <ak@linux.intel.com>
  26 Cc: Dave Hansen <dave.hansen@intel.com>
  27 Cc: Casey Schaufler <casey.schaufler@intel.com>
  28 Cc: Asit Mallick <asit.k.mallick@intel.com>
  29 Cc: Arjan van de Ven <arjan@linux.intel.com>
  30 Cc: Jon Masters <jcm@redhat.com>
  31 Cc: Waiman Long <longman9394@gmail.com>
  32 Cc: Greg KH <gregkh@linuxfoundation.org>
  33 Cc: Dave Stewart <david.c.stewart@intel.com>
  34 Cc: Kees Cook <keescook@chromium.org>
  35 Link: https://lkml.kernel.org/r/20181125185003.966801480@linutronix.de
  36 Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
  37 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  38 ---
  39  arch/x86/kernel/cpu/bugs.c | 7 +++++++
  40  1 file changed, 7 insertions(+)
  41
  42 diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
  43 index 64e5f64c3b38..364fd880feef 100644
  44 --- a/arch/x86/kernel/cpu/bugs.c
  45 +++ b/arch/x86/kernel/cpu/bugs.c
  46 @@ -325,6 +325,10 @@ static bool stibp_needed(void)
  47         if (spectre_v2_enabled == SPECTRE_V2_NONE)
  48                 return false;
  49
  50 +       /* Enhanced IBRS makes using STIBP unnecessary. */
  51 +       if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
  52 +               return false;
  53 +
  54         if (!boot_cpu_has(X86_FEATURE_STIBP))
  55                 return false;
  56
  57 @@ -852,6 +856,9 @@ static ssize_t l1tf_show_state(char *buf)
  58
  59  static char *stibp_state(void)
  60  {
  61 +       if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
  62 +               return "";
  63 +
  64         if (x86_spec_ctrl_base & SPEC_CTRL_STIBP)
  65                 return ", STIBP";
  66         else
  67 --
  68 2.21.0
  69