| Date | Wed, 21 Nov 2018 21:33:53 +0100 | From | Borislav Petkov <> | Subject | Re: [patch 05/24] x86/speculation: Disable STIBP when enhanced IBRS is in use |
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On Wed, Nov 21, 2018 at 09:14:35PM +0100, Thomas Gleixner wrote: > From: Tim Chen <tim.c.chen@linux.intel.com> > > 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> > > --- > arch/x86/kernel/cpu/bugs.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -321,6 +321,10 @@ 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; > > @@ -846,6 +850,9 @@ static ssize_t l1tf_show_state(char *buf > > static char *stibp_state(void) > { > + if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED) > + return "";
If spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED
then SPEC_CTRL_STIBP should not be set in x86_spec_ctrl_base (stibp_needed() prevents the setting in arch_smt_update()) so the above check should not be needed.
I *think*.
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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