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Subject[Patch v4 14/18] x86/speculation: Turn on or off STIBP according to a task's TIF_STIBP
Date
This patch creates the mechanism to apply STIBP protection on
a per task basis.

A new TIF_STIBP flag is created. Tasks needing STIBP would have the
TIF_STIBP flag applied. During context switch time, this flag is checked
and the STIBP bit in SPEC_CTRL MSR is updated according to changes in
this flag between previous and next tasks.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
arch/x86/include/asm/msr-index.h | 6 +++++-
arch/x86/include/asm/spec-ctrl.h | 12 ++++++++++++
arch/x86/include/asm/thread_info.h | 5 ++++-
arch/x86/kernel/process.c | 10 +++++++++-
4 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 4731f0c..bd19452 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -41,7 +41,11 @@

#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 */

diff --git a/arch/x86/include/asm/spec-ctrl.h b/arch/x86/include/asm/spec-ctrl.h
index 8e2f841..b593779 100644
--- 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(u64 tifn)
return (tifn & _TIF_SSBD) >> (TIF_SSBD - SPEC_CTRL_SSBD_SHIFT);
}

+static inline u64 stibp_tif_to_spec_ctrl(u64 tifn)
+{
+ BUILD_BUG_ON(TIF_STIBP < SPEC_CTRL_STIBP_SHIFT);
+ return (tifn & _TIF_STIBP) >> (TIF_STIBP - 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_STIBP < SPEC_CTRL_STIBP_SHIFT);
+ return (spec_ctrl & SPEC_CTRL_STIBP) << (TIF_STIBP - 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;
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 60798a0..4f6a7a9 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -110,6 +110,7 @@ struct thread_info {
/* Security mode */
#define TIF_SECCOMP 25 /* Secure computing */
#define TIF_SSBD 26 /* Speculative store bypass disable */
+#define TIF_STIBP 27 /* Single thread indirect branch speculation */

#define _TIF_NOCPUID (1 << TIF_NOCPUID)
#define _TIF_NOTSC (1 << TIF_NOTSC)
@@ -141,6 +142,7 @@ struct thread_info {

#define _TIF_SECCOMP (1 << TIF_SECCOMP)
#define _TIF_SSBD (1 << TIF_SSBD)
+#define _TIF_STIBP (1 << TIF_STIBP)

/*
* work to do in syscall_trace_enter(). Also includes TIF_NOHZ for
@@ -161,7 +163,8 @@ struct thread_info {

/* flags to check in __switch_to() */
#define _TIF_WORK_CTXSW \
- (_TIF_IO_BITMAP|_TIF_NOCPUID|_TIF_NOTSC|_TIF_BLOCKSTEP|_TIF_SSBD)
+ (_TIF_IO_BITMAP|_TIF_NOCPUID|_TIF_NOTSC|_TIF_BLOCKSTEP| \
+ _TIF_SSBD|_TIF_STIBP)

#define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY)
#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 74bef48..943e90d 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -406,6 +406,14 @@ 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);

+ /*
+ * Need STIBP defense against Spectre v2 attack
+ * if SMT is in use and enhanced IBRS is unsupported.
+ */
+ if (static_branch_likely(&cpu_smt_enabled) &&
+ !static_cpu_has(X86_FEATURE_USE_IBRS_ENHANCED))
+ msr |= stibp_tif_to_spec_ctrl(tifn);
+
wrmsrl(MSR_IA32_SPEC_CTRL, msr);
}

@@ -418,7 +426,7 @@ 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 = !!((tifp ^ tifn) & _TIF_STIBP);

/* If TIF_SSBD is different, select the proper mitigation method */
if ((tifp ^ tifn) & _TIF_SSBD) {
--
2.9.4
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