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From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: Andy Lutomirski <luto@kernel.org>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Markus T Metzger <markus.t.metzger@intel.com>,
	"Ravi V . Shankar" <ravi.v.shankar@intel.com>,
	"Chang S . Bae" <chang.seok.bae@intel.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH V2 01/15] x86/fsgsbase/64: Introduce FS/GS base helper functions
Date: Thu, 31 May 2018 10:58:31 -0700	[thread overview]
Message-ID: <1527789525-8857-2-git-send-email-chang.seok.bae@intel.com> (raw)
In-Reply-To: <1527789525-8857-1-git-send-email-chang.seok.bae@intel.com>

With new helpers, FS/GS base access is centralized.
Eventually, when FSGSBASE instruction enabled, it will
be faster.

The helpers are used on ptrace APIs (PTRACE_ARCH_PRCTL,
PTRACE_SETREG, PTRACE_GETREG, etc). Idea is to keep
the FS/GS-update mechanism organized.

Notion of "active" and "inactive" are used to distinguish
GS bases between "kernel" and "user". "inactive" GS base
is the GS base, backed up at kernel entries, of inactive
(user) task's.

Based-on-code-from: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/fsgsbase.h |  47 +++++++++++++++
 arch/x86/kernel/process_64.c    | 128 +++++++++++++++++++++++++++++-----------
 arch/x86/kernel/ptrace.c        |  28 +++------
 3 files changed, 149 insertions(+), 54 deletions(-)
 create mode 100644 arch/x86/include/asm/fsgsbase.h

diff --git a/arch/x86/include/asm/fsgsbase.h b/arch/x86/include/asm/fsgsbase.h
new file mode 100644
index 0000000..0d4fbef
--- /dev/null
+++ b/arch/x86/include/asm/fsgsbase.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_FSGSBASE_H
+#define _ASM_FSGSBASE_H 1
+
+#ifndef __ASSEMBLY__
+
+#ifdef CONFIG_X86_64
+
+#include <asm/msr-index.h>
+
+/*
+ * Read/write an (inactive) task's fsbase or gsbase. This returns
+ * the value that the FS/GS base would have (if the task were to be
+ * resumed). The current task is also supported.
+ */
+unsigned long read_task_fsbase(struct task_struct *task);
+unsigned long read_task_gsbase(struct task_struct *task);
+int write_task_fsbase(struct task_struct *task, unsigned long fsbase);
+int write_task_gsbase(struct task_struct *task, unsigned long gsbase);
+
+/* Helper functions for reading/writing FS/GS base */
+
+static inline unsigned long read_fsbase(void)
+{
+	unsigned long fsbase;
+
+	rdmsrl(MSR_FS_BASE, fsbase);
+	return fsbase;
+}
+
+void write_fsbase(unsigned long fsbase);
+
+static inline unsigned long read_inactive_gsbase(void)
+{
+	unsigned long gsbase;
+
+	rdmsrl(MSR_KERNEL_GS_BASE, gsbase);
+	return gsbase;
+}
+
+void  write_inactive_gsbase(unsigned long gsbase);
+
+#endif /* CONFIG_X86_64 */
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* _ASM_FSGSBASE_H */
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 12bb445..5506e1b 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -54,6 +54,7 @@
 #include <asm/vdso.h>
 #include <asm/intel_rdt_sched.h>
 #include <asm/unistd.h>
+#include <asm/fsgsbase.h>
 #ifdef CONFIG_IA32_EMULATION
 /* Not included via unistd.h */
 #include <asm/unistd_32_ia32.h>
@@ -278,6 +279,90 @@ static __always_inline void load_seg_legacy(unsigned short prev_index,
 	}
 }
 
+void write_fsbase(unsigned long fsbase)
+{
+	/* set the selector to 0 to not confuse __switch_to */
+	loadseg(FS, 0);
+	wrmsrl(MSR_FS_BASE, fsbase);
+}
+
+void write_inactive_gsbase(unsigned long gsbase)
+{
+	/* set the selector to 0 to not confuse __switch_to */
+	loadseg(GS, 0);
+	wrmsrl(MSR_KERNEL_GS_BASE, gsbase);
+}
+
+unsigned long read_task_fsbase(struct task_struct *task)
+{
+	unsigned long fsbase;
+
+	if (task == current)
+		fsbase = read_fsbase();
+	else
+		/*
+		 * XXX: This will not behave as expected if called
+		 * if fsindex != 0
+		 */
+		fsbase = task->thread.fsbase;
+
+	return fsbase;
+}
+
+unsigned long read_task_gsbase(struct task_struct *task)
+{
+	unsigned long gsbase;
+
+	if (task == current)
+		gsbase = read_inactive_gsbase();
+	else
+		/*
+		 * XXX: This will not behave as expected if called
+		 * if gsindex != 0
+		 */
+		gsbase = task->thread.gsbase;
+
+	return gsbase;
+}
+
+int write_task_fsbase(struct task_struct *task, unsigned long fsbase)
+{
+	int cpu;
+
+	/*
+	 * Not strictly needed for fs, but do it for symmetry
+	 * with gs
+	 */
+	if (unlikely(fsbase >= TASK_SIZE_MAX))
+		return -EPERM;
+
+	cpu = get_cpu();
+	task->thread.fsbase = fsbase;
+	if (task == current)
+		write_fsbase(fsbase);
+	task->thread.fsindex = 0;
+	put_cpu();
+
+	return 0;
+}
+
+int write_task_gsbase(struct task_struct *task, unsigned long gsbase)
+{
+	int cpu;
+
+	if (unlikely(gsbase >= TASK_SIZE_MAX))
+		return -EPERM;
+
+	cpu = get_cpu();
+	task->thread.gsbase = gsbase;
+	if (task == current)
+		write_inactive_gsbase(gsbase);
+	task->thread.gsindex = 0;
+	put_cpu();
+
+	return 0;
+}
+
 int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
 		unsigned long arg, struct task_struct *p, unsigned long tls)
 {
@@ -618,54 +703,27 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
 long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
 {
 	int ret = 0;
-	int doit = task == current;
-	int cpu;
 
 	switch (option) {
-	case ARCH_SET_GS:
-		if (arg2 >= TASK_SIZE_MAX)
-			return -EPERM;
-		cpu = get_cpu();
-		task->thread.gsindex = 0;
-		task->thread.gsbase = arg2;
-		if (doit) {
-			load_gs_index(0);
-			ret = wrmsrl_safe(MSR_KERNEL_GS_BASE, arg2);
-		}
-		put_cpu();
+	case ARCH_SET_GS: {
+		ret = write_task_gsbase(task, arg2);
 		break;
-	case ARCH_SET_FS:
-		/* Not strictly needed for fs, but do it for symmetry
-		   with gs */
-		if (arg2 >= TASK_SIZE_MAX)
-			return -EPERM;
-		cpu = get_cpu();
-		task->thread.fsindex = 0;
-		task->thread.fsbase = arg2;
-		if (doit) {
-			/* set the selector to 0 to not confuse __switch_to */
-			loadsegment(fs, 0);
-			ret = wrmsrl_safe(MSR_FS_BASE, arg2);
-		}
-		put_cpu();
+	}
+	case ARCH_SET_FS: {
+		ret = write_task_fsbase(task, arg2);
 		break;
+	}
 	case ARCH_GET_FS: {
 		unsigned long base;
 
-		if (doit)
-			rdmsrl(MSR_FS_BASE, base);
-		else
-			base = task->thread.fsbase;
+		base = read_task_fsbase(task);
 		ret = put_user(base, (unsigned long __user *)arg2);
 		break;
 	}
 	case ARCH_GET_GS: {
 		unsigned long base;
 
-		if (doit)
-			rdmsrl(MSR_KERNEL_GS_BASE, base);
-		else
-			base = task->thread.gsbase;
+		base = read_task_gsbase(task);
 		ret = put_user(base, (unsigned long __user *)arg2);
 		break;
 	}
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index ed5c4cd..b2f0beb 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -39,6 +39,7 @@
 #include <asm/hw_breakpoint.h>
 #include <asm/traps.h>
 #include <asm/syscall.h>
+#include <asm/fsgsbase.h>
 
 #include "tls.h"
 
@@ -396,12 +397,11 @@ static int putreg(struct task_struct *child,
 		if (value >= TASK_SIZE_MAX)
 			return -EIO;
 		/*
-		 * When changing the segment base, use do_arch_prctl_64
-		 * to set either thread.fs or thread.fsindex and the
-		 * corresponding GDT slot.
+		 * When changing the FS base, use the same
+		 * mechanism as for do_arch_prctl_64
 		 */
 		if (child->thread.fsbase != value)
-			return do_arch_prctl_64(child, ARCH_SET_FS, value);
+			return write_task_fsbase(child, value);
 		return 0;
 	case offsetof(struct user_regs_struct,gs_base):
 		/*
@@ -410,7 +410,7 @@ static int putreg(struct task_struct *child,
 		if (value >= TASK_SIZE_MAX)
 			return -EIO;
 		if (child->thread.gsbase != value)
-			return do_arch_prctl_64(child, ARCH_SET_GS, value);
+			return write_task_gsbase(child, value);
 		return 0;
 #endif
 	}
@@ -434,20 +434,10 @@ static unsigned long getreg(struct task_struct *task, unsigned long offset)
 		return get_flags(task);
 
 #ifdef CONFIG_X86_64
-	case offsetof(struct user_regs_struct, fs_base): {
-		/*
-		 * XXX: This will not behave as expected if called on
-		 * current or if fsindex != 0.
-		 */
-		return task->thread.fsbase;
-	}
-	case offsetof(struct user_regs_struct, gs_base): {
-		/*
-		 * XXX: This will not behave as expected if called on
-		 * current or if fsindex != 0.
-		 */
-		return task->thread.gsbase;
-	}
+	case offsetof(struct user_regs_struct, fs_base):
+		return read_task_fsbase(task);
+	case offsetof(struct user_regs_struct, gs_base):
+		return read_task_gsbase(task);
 #endif
 	}
 
-- 
2.7.4

  reply	other threads:[~2018-05-31 17:59 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-31 17:58 [PATCH V2 00/15] x86: Enable FSGSBASE instructions Chang S. Bae
2018-05-31 17:58 ` Chang S. Bae [this message]
2018-05-31 20:14   ` [PATCH V2 01/15] x86/fsgsbase/64: Introduce FS/GS base helper functions Andy Lutomirski
2018-05-31 21:03     ` Bae, Chang Seok
2018-05-31 17:58 ` [PATCH V2 02/15] x86/fsgsbase/64: Make ptrace read FS/GS base accurately Chang S. Bae
2018-05-31 20:14   ` Andy Lutomirski
2018-05-31 20:31     ` hpa
2018-05-31 20:38       ` Andy Lutomirski
2018-05-31 17:58 ` [PATCH V2 03/15] x86/fsgsbase/64: Use FS/GS base helpers in core dump Chang S. Bae
2018-05-31 20:15   ` Andy Lutomirski
2018-05-31 21:03     ` Bae, Chang Seok
2018-05-31 17:58 ` [PATCH V2 04/15] x86/fsgsbase/64: Factor out load FS/GS segments from __switch_to Chang S. Bae
2018-05-31 20:16   ` Andy Lutomirski
2018-05-31 17:58 ` [PATCH V2 05/15] x86/vdso: Move out the CPU number store Chang S. Bae
2018-05-31 20:25   ` Andy Lutomirski
2018-05-31 21:06     ` Bae, Chang Seok
2018-06-05  7:02   ` [lkp-robot] [x86/vdso] f52001961d: BUG:kernel_hang_in_early-boot_stage,last_printk:Probing_EDD(edd=off_to_disable)...ok kernel test robot
2018-05-31 17:58 ` [PATCH V2 06/15] taint: Add taint for insecure Chang S. Bae
2018-05-31 20:25   ` Andy Lutomirski
2018-05-31 20:50     ` hpa
2018-05-31 17:58 ` [PATCH V2 07/15] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 08/15] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 09/15] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 10/15] x86/fsgsbase/64: Preserve FS/GS state in __switch_to if FSGSBASE is on Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 11/15] x86/fsgsbase/64: When copying a thread, use FSGSBASE if enabled Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 12/15] x86/fsgsbase/64: Use per-CPU base as GS base on paranoid_entry Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 13/15] x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 14/15] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Chang S. Bae
2018-05-31 17:58 ` [PATCH V2 15/15] x86/fsgsbase/64: Add documentation for FSGSBASE Chang S. Bae
2018-05-31 20:37 ` [PATCH V2 00/15] x86: Enable FSGSBASE instructions Andy Lutomirski
2018-05-31 21:11   ` Bae, Chang Seok

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