On Tue, 20 Nov 2018, Tim Chen wrote:
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 74bef48..48fcd46 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -406,6 +406,8 @@ static __always_inline void spec_ctrl_update_msr(unsigned
> long tifn)
> if (static_cpu_has(X86_FEATURE_SSBD))
> msr |= ssbd_tif_to_spec_ctrl(tifn);
>
> + msr |= stibp_tif_to_spec_ctrl(tifn);
This is wrong. If STIBP is disabled, but the TIF flag is set to control
IBPB and this path is entered to handle a SSBD change, then this will set
STIBP as well.
> +
> wrmsrl(MSR_IA32_SPEC_CTRL, msr);
> }
>
> @@ -418,7 +420,17 @@ static __always_inline void
> spec_ctrl_update_msr(unsigned long tifn)
> static __always_inline void __speculation_ctrl_update(unsigned long tifp,
> unsigned long tifn)
> {
> - bool updmsr = false;
> + bool updmsr;
> +
> + /*
> + * Need STIBP defense against Spectre v2 attack
> + * if SMT is in use and enhanced IBRS is unsupported.
> + */
> + if (static_cpu_has(X86_FEATURE_STIBP) && cpu_use_smt_and_hotplug &&
> + !static_cpu_has(X86_FEATURE_USE_IBRS_ENHANCED))
> + updmsr = !!((tifp ^ tifn) & _TIF_SPEC_INDIR_BRANCH);
At the end of the series this has then two alternative patch bits and two
static keys. This can be done with a single static key which is controlled
from the bug code.
I'll send out a cleaned up version of that stuff later today.
Thanks,
tglx
