Introduce user-mode Indirect Branch Tracking (IBT) support. Add routines
for the setup/disable of IBT.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
---
v28:
- When IBT feature is not present, make ibt_setup() return success,
since this is a setup function.
v27:
- Change struct thread_shstk: ibt_enabled to ibt.
- Create a helper for set/clear bits of MSR_IA32_U_CET.
---
arch/x86/include/asm/cet.h | 9 ++++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/ibt.c | 58 ++++++++++++++++++++++++++++++++++++++
3 files changed, 68 insertions(+)
create mode 100644 arch/x86/kernel/ibt.c
diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index c76a85fbd59f..3dfca29a7c0b 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -14,6 +14,7 @@ struct thread_shstk {
u64 base;
u64 size;
u64 locked:1;
+ u64 ibt:1;
};
#ifdef CONFIG_X86_SHADOW_STACK
@@ -42,6 +43,14 @@ static inline int setup_signal_shadow_stack(int ia32, void __user *restorer) { r
static inline int restore_signal_shadow_stack(void) { return 0; }
#endif
+#ifdef CONFIG_X86_IBT
+int ibt_setup(void);
+void ibt_disable(void);
+#else
+static inline int ibt_setup(void) { return 0; }
+static inline void ibt_disable(void) {}
+#endif
+
#ifdef CONFIG_X86_SHADOW_STACK
int prctl_cet(int option, u64 arg2);
#else
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 39e826b5cabd..cce07a920fec 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -152,6 +152,7 @@ obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o
obj-$(CONFIG_AMD_MEM_ENCRYPT) += sev.o
obj-$(CONFIG_X86_SHADOW_STACK) += shstk.o
obj-$(CONFIG_X86_SHADOW_STACK) += shstk.o cet_prctl.o
+obj-$(CONFIG_X86_IBT) += ibt.o
###
# 64 bit specific files
ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/ibt.c b/arch/x86/kernel/ibt.c
new file mode 100644
index 000000000000..4ab7af33b274
--- /dev/null
+++ b/arch/x86/kernel/ibt.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ibt.c - Intel Indirect Branch Tracking support
+ *
+ * Copyright (c) 2021, Intel Corporation.
+ * Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
+ */
+
+#include <linux/user.h>
+#include <asm/fpu/internal.h>
+#include <asm/fpu/xstate.h>
+#include <asm/fpu/types.h>
+#include <asm/msr.h>
+#include <asm/cet.h>
+
+static int ibt_set_clear_msr_bits(u64 set, u64 clear)
+{
+ u64 msr;
+ int r;
+
+ fpregs_lock();
+
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ fpregs_restore_userregs();
+
+ r = rdmsrl_safe(MSR_IA32_U_CET, &msr);
+ if (!r) {
+ msr = (msr & ~clear) | set;
+ r = wrmsrl_safe(MSR_IA32_U_CET, msr);
+ }
+
+ fpregs_unlock();
+
+ return r;
+}
+
+int ibt_setup(void)
+{
+ int r;
+
+ if (!cpu_feature_enabled(X86_FEATURE_IBT))
+ return 0;
+
+ r = ibt_set_clear_msr_bits(CET_ENDBR_EN | CET_NO_TRACK_EN, 0);
+ if (!r)
+ current->thread.shstk.ibt = 1;
+
+ return r;
+}
+
+void ibt_disable(void)
+{
+ if (!current->thread.shstk.ibt)
+ return;
+
+ ibt_set_clear_msr_bits(0, CET_ENDBR_EN);
+ current->thread.shstk.ibt = 0;
+}
--
2.21.0
