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Subject[PATCH 2/2] x86/speculation: Provide application property based STIBP protection
Date
This patch provides an application property based spectre_v2
protection with STIBP against attack from another app from
a sibling hyper-thread. For security sensitive non-dumpable
app, STIBP will be turned on before switching to it for Intel
processors vulnerable to spectre_v2.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
arch/x86/include/asm/msr-index.h | 3 ++-
arch/x86/include/asm/spec-ctrl.h | 12 ++++++++++++
arch/x86/include/asm/thread_info.h | 4 +++-
arch/x86/kernel/cpu/bugs.c | 12 ++++++++++--
arch/x86/kernel/process.c | 9 +++++----
arch/x86/mm/tlb.c | 22 ++++++++++++++++++++++
6 files changed, 54 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 4731f0c..0e43388 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -41,7 +41,8 @@

#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 bit */
+#define SPEC_CTRL_STIBP (1 << SPEC_CTRL_STIBP_SHIFT) /* Single Thread Indirect Branch Predictors */
#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 ae7c2c5..6a962b8 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 2ff2a30..40c58c286 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -83,6 +83,7 @@ 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_STIBP 9 /* Single threaded indirect branch predict */
#define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */
#define TIF_UPROBE 12 /* breakpointed or singlestepping */
#define TIF_PATCH_PENDING 13 /* pending live patching update */
@@ -110,6 +111,7 @@ 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_STIBP (1 << TIF_STIBP)
#define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY)
#define _TIF_UPROBE (1 << TIF_UPROBE)
#define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING)
@@ -146,7 +148,7 @@ 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/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index c967012..358f2b1 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -187,6 +187,9 @@ x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
static_cpu_has(X86_FEATURE_AMD_SSBD))
hostval |= ssbd_tif_to_spec_ctrl(ti->flags);

+ if (static_branch_unlikely(&spectre_v2_app_lite))
+ hostval |= stibp_tif_to_spec_ctrl(ti->flags);
+
if (hostval != guestval) {
msrval = setguest ? guestval : hostval;
wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
@@ -383,6 +386,11 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)

static bool stibp_needed(void)
{
+ /*
+ * Determine if we want to leave STIBP always on.
+ * For lite option, we enable STIBP based on a process's
+ * flag during context switch.
+ */
if (static_branch_unlikely(&spectre_v2_app_lite))
return false;

@@ -958,14 +966,14 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
ret = sprintf(buf, "%s%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB-lite" : "",
boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",
- (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "",
+ ", STIBP-lite",
boot_cpu_has(X86_FEATURE_RSB_CTXSW) ? ", RSB filling" : "",
spectre_v2_module_string());
else
ret = sprintf(buf, "%s%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB-strict" : "",
boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",
- (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "",
+ (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP-strict" : "",
boot_cpu_has(X86_FEATURE_RSB_CTXSW) ? ", RSB filling" : "",
spectre_v2_module_string());
mutex_unlock(&spec_ctrl_mutex);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c93fcfd..878301d 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -395,9 +395,10 @@ static __always_inline void amd_set_ssb_virt_state(unsigned long tifn)
wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, ssbd_tif_to_spec_ctrl(tifn));
}

-static __always_inline void intel_set_ssb_state(unsigned long tifn)
+static __always_inline void intel_set_spec_ctrl_state(unsigned long tifn)
{
- u64 msr = x86_spec_ctrl_base | ssbd_tif_to_spec_ctrl(tifn);
+ u64 msr = x86_spec_ctrl_base | ssbd_tif_to_spec_ctrl(tifn)
+ | stibp_tif_to_spec_ctrl(tifn);

wrmsrl(MSR_IA32_SPEC_CTRL, msr);
}
@@ -409,7 +410,7 @@ static __always_inline void __speculative_store_bypass_update(unsigned long tifn
else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD))
amd_set_core_ssb_state(tifn);
else
- intel_set_ssb_state(tifn);
+ intel_set_spec_ctrl_state(tifn);
}

void speculative_store_bypass_update(unsigned long tif)
@@ -451,7 +452,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
if ((tifp ^ tifn) & _TIF_NOCPUID)
set_cpuid_faulting(!!(tifn & _TIF_NOCPUID));

- if ((tifp ^ tifn) & _TIF_SSBD)
+ if ((tifp ^ tifn) & (_TIF_SSBD | _TIF_STIBP))
__speculative_store_bypass_update(tifn);
}

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 54780a8..dd70bb4 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -205,6 +205,25 @@ static bool ibpb_needed(struct task_struct *tsk, u64 last_ctx_id)
return (__ptrace_may_access(tsk, PTRACE_MODE_IBPB));
}

+static void set_stibp(struct task_struct *tsk)
+{
+ /*
+ * For lite protection mode, we set STIBP only
+ * for non-dumpable processes.
+ */
+
+ if (!static_branch_unlikely(&spectre_v2_app_lite))
+ return;
+
+ if (!tsk || !tsk->mm)
+ return;
+
+ if (get_dumpable(tsk->mm) != SUID_DUMP_USER)
+ test_and_set_tsk_thread_flag(tsk, TIF_STIBP);
+ else
+ test_and_clear_tsk_thread_flag(tsk, TIF_STIBP);
+}
+
void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *tsk)
{
@@ -296,6 +315,9 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
ibpb_needed(tsk, last_ctx_id))
indirect_branch_prediction_barrier();

+ if (static_cpu_has(X86_FEATURE_STIBP))
+ set_stibp(tsk);
+
if (IS_ENABLED(CONFIG_VMAP_STACK)) {
/*
* If our current stack is in vmalloc space and isn't
--
2.9.4
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