From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> commit 5bfbe3ad5840d941b89bcac54b821ba14f50a0ba upstream. To avoid the overhead of STIBP always on, it's necessary to allow per task control of STIBP. Add a new task flag TIF_SPEC_IB and evaluate it during context switch if SMT is active and flag evaluation is enabled by the speculation control code. Add the conditional evaluation to x86_virt_spec_ctrl() as well so the guest/host switch works properly. This has no effect because TIF_SPEC_IB cannot be set yet and the static key which controls evaluation is off. Preparatory patch for adding the control code. [ tglx: Simplify the context switch logic and make the TIF evaluation depend on SMP=y and on the static key controlling the conditional update. Rename it to TIF_SPEC_IB because it controls both STIBP and IBPB ] Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Jiri Kosina <jkosina@xxxxxxx> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: David Woodhouse <dwmw@xxxxxxxxxxxx> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Cc: Casey Schaufler <casey.schaufler@xxxxxxxxx> Cc: Asit Mallick <asit.k.mallick@xxxxxxxxx> Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> Cc: Jon Masters <jcm@xxxxxxxxxx> Cc: Waiman Long <longman9394@xxxxxxxxx> Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Dave Stewart <david.c.stewart@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20181125185005.176917199@xxxxxxxxxxxxx [bwh: Backported to 4.4: adjust context] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/include/asm/msr-index.h | 5 +++-- arch/x86/include/asm/spec-ctrl.h | 12 ++++++++++++ arch/x86/include/asm/thread_info.h | 5 ++++- arch/x86/kernel/cpu/bugs.c | 4 ++++ arch/x86/kernel/process.c | 20 ++++++++++++++++++-- 5 files changed, 41 insertions(+), 5 deletions(-) --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -34,9 +34,10 @@ /* Intel MSRs. Some also available on other CPUs */ #define MSR_IA32_SPEC_CTRL 0x00000048 /* Speculation Control */ #define SPEC_CTRL_IBRS (1 << 0) /* Indirect Branch Restricted Speculation */ -#define SPEC_CTRL_STIBP (1 << 1) /* Single Thread Indirect Branch Predictors */ +#define SPEC_CTRL_STIBP_SHIFT 1 /* Single Thread Indirect Branch Predictor (STIBP) bit */ +#define SPEC_CTRL_STIBP (1 << SPEC_CTRL_STIBP_SHIFT) /* STIBP mask */ #define SPEC_CTRL_SSBD_SHIFT 2 /* Speculative Store Bypass Disable bit */ -#define SPEC_CTRL_SSBD (1 << SPEC_CTRL_SSBD_SHIFT) /* Speculative Store Bypass Disable */ +#define SPEC_CTRL_SSBD (1 << SPEC_CTRL_SSBD_SHIFT) /* Speculative Store Bypass Disable */ #define MSR_IA32_PRED_CMD 0x00000049 /* Prediction Command */ #define PRED_CMD_IBPB (1 << 0) /* Indirect Branch Prediction Barrier */ --- a/arch/x86/include/asm/spec-ctrl.h +++ b/arch/x86/include/asm/spec-ctrl.h @@ -53,12 +53,24 @@ static inline u64 ssbd_tif_to_spec_ctrl( return (tifn & _TIF_SSBD) >> (TIF_SSBD - SPEC_CTRL_SSBD_SHIFT); } +static inline u64 stibp_tif_to_spec_ctrl(u64 tifn) +{ + BUILD_BUG_ON(TIF_SPEC_IB < SPEC_CTRL_STIBP_SHIFT); + return (tifn & _TIF_SPEC_IB) >> (TIF_SPEC_IB - SPEC_CTRL_STIBP_SHIFT); +} + static inline unsigned long ssbd_spec_ctrl_to_tif(u64 spec_ctrl) { BUILD_BUG_ON(TIF_SSBD < SPEC_CTRL_SSBD_SHIFT); return (spec_ctrl & SPEC_CTRL_SSBD) << (TIF_SSBD - SPEC_CTRL_SSBD_SHIFT); } +static inline unsigned long stibp_spec_ctrl_to_tif(u64 spec_ctrl) +{ + BUILD_BUG_ON(TIF_SPEC_IB < SPEC_CTRL_STIBP_SHIFT); + return (spec_ctrl & SPEC_CTRL_STIBP) << (TIF_SPEC_IB - SPEC_CTRL_STIBP_SHIFT); +} + static inline u64 ssbd_tif_to_amd_ls_cfg(u64 tifn) { return (tifn & _TIF_SSBD) ? x86_amd_ls_cfg_ssbd_mask : 0ULL; --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -96,6 +96,7 @@ struct thread_info { #define TIF_SYSCALL_EMU 6 /* syscall emulation active */ #define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */ #define TIF_SECCOMP 8 /* secure computing */ +#define TIF_SPEC_IB 9 /* Indirect branch speculation mitigation */ #define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */ #define TIF_UPROBE 12 /* breakpointed or singlestepping */ #define TIF_NOTSC 16 /* TSC is not accessible in userland */ @@ -121,6 +122,7 @@ struct thread_info { #define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU) #define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT) #define _TIF_SECCOMP (1 << TIF_SECCOMP) +#define _TIF_SPEC_IB (1 << TIF_SPEC_IB) #define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY) #define _TIF_UPROBE (1 << TIF_UPROBE) #define _TIF_NOTSC (1 << TIF_NOTSC) @@ -149,7 +151,8 @@ struct thread_info { /* flags to check in __switch_to() */ #define _TIF_WORK_CTXSW \ - (_TIF_IO_BITMAP|_TIF_NOTSC|_TIF_BLOCKSTEP|_TIF_SSBD) + (_TIF_IO_BITMAP|_TIF_NOTSC|_TIF_BLOCKSTEP| \ + _TIF_SSBD|_TIF_SPEC_IB) #define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY) #define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW) --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -139,6 +139,10 @@ x86_virt_spec_ctrl(u64 guest_spec_ctrl, static_cpu_has(X86_FEATURE_AMD_SSBD)) hostval |= ssbd_tif_to_spec_ctrl(ti->flags); + /* Conditional STIBP enabled? */ + if (static_branch_unlikely(&switch_to_cond_stibp)) + hostval |= stibp_tif_to_spec_ctrl(ti->flags); + if (hostval != guestval) { msrval = setguest ? guestval : hostval; wrmsrl(MSR_IA32_SPEC_CTRL, msrval); --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -326,11 +326,17 @@ static __always_inline void amd_set_ssb_ static __always_inline void __speculation_ctrl_update(unsigned long tifp, unsigned long tifn) { + unsigned long tif_diff = tifp ^ tifn; u64 msr = x86_spec_ctrl_base; bool updmsr = false; - /* If TIF_SSBD is different, select the proper mitigation method */ - if ((tifp ^ tifn) & _TIF_SSBD) { + /* + * If TIF_SSBD is different, select the proper mitigation + * method. Note that if SSBD mitigation is disabled or permanentely + * enabled this branch can't be taken because nothing can set + * TIF_SSBD. + */ + if (tif_diff & _TIF_SSBD) { if (static_cpu_has(X86_FEATURE_VIRT_SSBD)) { amd_set_ssb_virt_state(tifn); } else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD)) { @@ -342,6 +348,16 @@ static __always_inline void __speculatio } } + /* + * Only evaluate TIF_SPEC_IB if conditional STIBP is enabled, + * otherwise avoid the MSR write. + */ + if (IS_ENABLED(CONFIG_SMP) && + static_branch_unlikely(&switch_to_cond_stibp)) { + updmsr |= !!(tif_diff & _TIF_SPEC_IB); + msr |= stibp_tif_to_spec_ctrl(tifn); + } + if (updmsr) wrmsrl(MSR_IA32_SPEC_CTRL, msr); }
