[RFC PATCH v9 2/7] x86/cet/ibt: User-mode Indirect Branch Tracking support

Yu-cheng Yu
2020-02-05T18:23:27Z

Introduce user-mode Indirect Branch Tracking (IBT) support. Update setup
routines to include IBT.

v9:
- Change cpu_feature_enabled() to static_cpu_has().

v2:
- Change noibt to no_cet_ibt.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/include/asm/cet.h | 5 +++
arch/x86/include/asm/disabled-features.h | 8 ++++-
arch/x86/kernel/cet.c | 34 +++++++++++++++++++
arch/x86/kernel/cpu/common.c | 17 ++++++++++
.../arch/x86/include/asm/disabled-features.h | 8 ++++-
5 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index b64f6d810ae0..d3f0d50d51ec 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -16,6 +16,9 @@ struct cet_status {
unsigned long shstk_size;
unsigned int locked:1;
unsigned int shstk_enabled:1;
+ unsigned int ibt_enabled:1;
+ unsigned int ibt_bitmap_used:1;
+ unsigned long ibt_bitmap_base;
};

#ifdef CONFIG_X86_INTEL_CET
@@ -26,6 +29,8 @@ int cet_alloc_shstk(unsigned long *arg);
void cet_disable_free_shstk(struct task_struct *p);
int cet_restore_signal(bool ia32, struct sc_ext *sc);
int cet_setup_signal(bool ia32, unsigned long rstor, struct sc_ext *sc);
+int cet_setup_ibt(void);
+void cet_disable_ibt(void);
#else
static inline int prctl_cet(int option, unsigned long arg2) { return -EINVAL; }
static inline int cet_setup_thread_shstk(struct task_struct *p) { return 0; }
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index e1454509ad83..09f81a09dae7 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -68,6 +68,12 @@
#define DISABLE_SHSTK (1<<(X86_FEATURE_SHSTK & 31))
#endif

+#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+#define DISABLE_IBT 0
+#else
+#define DISABLE_IBT (1<<(X86_FEATURE_IBT & 31))
+#endif
+
/*
* Make sure to add features to the correct mask
*/
@@ -89,7 +95,7 @@
#define DISABLED_MASK15 0
#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP|DISABLE_SHSTK)
#define DISABLED_MASK17 0
-#define DISABLED_MASK18 0
+#define DISABLED_MASK18 (DISABLE_IBT)
#define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)

#endif /* _ASM_X86_DISABLED_FEATURES_H */
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
index 01aa24c40a5d..26f5d7c4fbff 100644
--- a/arch/x86/kernel/cet.c
+++ b/arch/x86/kernel/cet.c
@@ -13,6 +13,8 @@
#include <linux/uaccess.h>
#include <linux/sched/signal.h>
#include <linux/compat.h>
+#include <linux/vmalloc.h>
+#include <linux/bitops.h>
#include <asm/msr.h>
#include <asm/user.h>
#include <asm/fpu/internal.h>
@@ -342,3 +344,35 @@ int cet_setup_signal(bool ia32, unsigned long rstor_addr, struct sc_ext *sc_ext)
end_update_msrs();

return 0;
+}
+
+int cet_setup_ibt(void)
+{
+ u64 msr_val;
+
+ if (!static_cpu_has(X86_FEATURE_IBT))
+ return -EOPNOTSUPP;
+
+ start_update_msrs();
+ rdmsrl(MSR_IA32_U_CET, msr_val);
+ msr_val |= (MSR_IA32_CET_ENDBR_EN | MSR_IA32_CET_NO_TRACK_EN);
+ wrmsrl(MSR_IA32_U_CET, msr_val);
+ end_update_msrs();
+ current->thread.cet.ibt_enabled = 1;
+ return 0;
+}
+
+void cet_disable_ibt(void)
+{
+ u64 msr_val;
+
+ if (!static_cpu_has(X86_FEATURE_IBT))
+ return;
+
+ start_update_msrs();
+ rdmsrl(MSR_IA32_U_CET, msr_val);
+ msr_val &= MSR_IA32_CET_SHSTK_EN;
+ wrmsrl(MSR_IA32_U_CET, msr_val);
+ end_update_msrs();
+ current->thread.cet.ibt_enabled = 0;
+}
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 40498ec72fda..c1ffde5c2ace 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -510,6 +510,23 @@ static __init int setup_disable_shstk(char *s)
__setup("no_cet_shstk", setup_disable_shstk);
#endif

+#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+static __init int setup_disable_ibt(char *s)
+{
+ /* require an exact match without trailing characters */
+ if (s[0] != '\0')
+ return 0;
+
+ if (!boot_cpu_has(X86_FEATURE_IBT))
+ return 1;
+
+ setup_clear_cpu_cap(X86_FEATURE_IBT);
+ pr_info("x86: 'no_cet_ibt' specified, disabling Branch Tracking\n");
+ return 1;
+}
+__setup("no_cet_ibt", setup_disable_ibt);
+#endif
+
/*
* Some CPU features depend on higher CPUID levels, which may not always
* be available due to CPUID level capping or broken virtualization
diff --git a/tools/arch/x86/include/asm/disabled-features.h b/tools/arch/x86/include/asm/disabled-features.h
index e1454509ad83..09f81a09dae7 100644
--- a/tools/arch/x86/include/asm/disabled-features.h
+++ b/tools/arch/x86/include/asm/disabled-features.h
@@ -68,6 +68,12 @@
#define DISABLE_SHSTK (1<<(X86_FEATURE_SHSTK & 31))
#endif

+#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+#define DISABLE_IBT 0
+#else
+#define DISABLE_IBT (1<<(X86_FEATURE_IBT & 31))
+#endif
+
/*
* Make sure to add features to the correct mask
*/
@@ -89,7 +95,7 @@
#define DISABLED_MASK15 0
#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP|DISABLE_SHSTK)
#define DISABLED_MASK17 0
-#define DISABLED_MASK18 0
+#define DISABLED_MASK18 (DISABLE_IBT)
#define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)

#endif /* _ASM_X86_DISABLED_FEATURES_H */
--
2.21.0