linux-kernel - [PATCH v24 2/9] x86/cet/ibt: Add user-mode Indirect Branch Tracking support

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Date:   Thu,  1 Apr 2021 15:13:56 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v24 2/9] x86/cet/ibt: Add user-mode Indirect Branch Tracking support

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@...el.com>
Cc: Kees Cook <keescook@...omium.org>
---
v24:
- Move IBT routines to a separate ibt.c, update related areas accordingly.

 arch/x86/include/asm/cet.h |  9 ++++++
 arch/x86/kernel/Makefile   |  1 +
 arch/x86/kernel/ibt.c      | 57 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 67 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 26124820d46f..b3df306699b4 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -15,6 +15,7 @@ struct cet_status {
 	unsigned long	shstk_base;
 	unsigned long	shstk_size;
 	unsigned int	locked:1;
+	unsigned int	ibt_enabled:1;
 };
 
 #ifdef CONFIG_X86_SHADOW_STACK
@@ -41,6 +42,14 @@ static inline int shstk_check_rstor_token(bool ia32, unsigned long token_addr,
 					  unsigned long *new_ssp) { 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_CET
 int prctl_cet(int option, u64 arg2);
 #else
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 868cb3aac618..9653e422d0f3 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-es.o
 obj-$(CONFIG_X86_SHADOW_STACK)		+= shstk.o
 obj-$(CONFIG_X86_CET)			+= cet_prctl.o
+obj-$(CONFIG_X86_IBT)			+= ibt.o
 
 ###
 # 64 bit specific files
diff --git a/arch/x86/kernel/ibt.c b/arch/x86/kernel/ibt.c
new file mode 100644
index 000000000000..d2cef1a0345b
--- /dev/null
+++ b/arch/x86/kernel/ibt.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ibt.c - Intel Indirect Branch Tracking support
+ *
+ * Copyright (c) 2021, Intel Corporation.
+ * Yu-cheng Yu <yu-cheng.yu@...el.com>
+ */
+
+#include <linux/user.h>
+#include <asm/msr.h>
+#include <asm/fpu/internal.h>
+#include <asm/fpu/xstate.h>
+#include <asm/fpu/types.h>
+#include <asm/cet.h>
+
+static void start_update_msrs(void)
+{
+	fpregs_lock();
+	if (test_thread_flag(TIF_NEED_FPU_LOAD))
+		__fpregs_load_activate();
+}
+
+static void end_update_msrs(void)
+{
+	fpregs_unlock();
+}
+
+int ibt_setup(void)
+{
+	u64 msr_val;
+
+	if (!cpu_feature_enabled(X86_FEATURE_IBT))
+		return -EOPNOTSUPP;
+
+	start_update_msrs();
+	rdmsrl(MSR_IA32_U_CET, msr_val);
+	msr_val |= (CET_ENDBR_EN | CET_NO_TRACK_EN);
+	wrmsrl(MSR_IA32_U_CET, msr_val);
+	end_update_msrs();
+	current->thread.cet.ibt_enabled = 1;
+	return 0;
+}
+
+void ibt_disable(void)
+{
+	u64 msr_val;
+
+	if (!cpu_feature_enabled(X86_FEATURE_IBT))
+		return;
+
+	start_update_msrs();
+	rdmsrl(MSR_IA32_U_CET, msr_val);
+	msr_val &= ~CET_ENDBR_EN;
+	wrmsrl(MSR_IA32_U_CET, msr_val);
+	end_update_msrs();
+	current->thread.cet.ibt_enabled = 0;
+}
-- 
2.21.0