x86/speculation: Disable STIBP when enhanced IBRS is in use

If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2
user space exploits from hyperthread sibling.

Disable STIBP when enhanced IBRS is used.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Casey Schaufler <casey.schaufler@intel.com>
Cc: Asit Mallick <asit.k.mallick@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Waiman Long <longman9394@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Dave Stewart <david.c.stewart@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181125185003.966801480@linutronix.de
CVE-2017-5715

(cherry picked from commit 34bce7c9690b1d897686aac89604ba7adc365556)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b9d278730fbe24aeeff0ac0477d2a4134baef672..feaf50c33001cd6db63d2aa9838e18fece98a387 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -319,6 +319,10 @@ static bool stibp_needed(void)
        if (spectre_v2_enabled == SPECTRE_V2_NONE)
                return false;
 
+       /* Enhanced IBRS makes using STIBP unnecessary. */
+       if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+               return false;
+
        if (!boot_cpu_has(X86_FEATURE_STIBP))
                return false;
 
@@ -840,6 +844,9 @@ static ssize_t l1tf_show_state(char *buf)
 
 static char *stibp_state(void)
 {
+       if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+               return "";
+
        if (x86_spec_ctrl_base & SPEC_CTRL_STIBP)
                return ", STIBP";
        else