7 files changed, 109 insertions, 2 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 7f418bbc261a..4e312fffbfd7 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -83,6 +83,13 @@ config KRETPROBES
         def_bool y
         depends on KPROBES && HAVE_KRETPROBES
 
+config USER_RETURN_NOTIFIER
+        bool
+        depends on HAVE_USER_RETURN_NOTIFIER
+        help
+          Provide a kernel-internal notification when a cpu is about to
+          switch to user mode.
+
 config HAVE_IOREMAP_PROT
         bool
 
@@ -126,4 +133,7 @@ config HAVE_DMA_API_DEBUG
 config HAVE_DEFAULT_NO_SPIN_MUTEXES
         bool
 
+config HAVE_USER_RETURN_NOTIFIER
+        bool
+
 source "kernel/gcov/Kconfig"
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8da93745c087..1df175d15aa8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -50,6 +50,7 @@ config X86
         select HAVE_KERNEL_BZIP2
         select HAVE_KERNEL_LZMA
         select HAVE_ARCH_KMEMCHECK
+        select HAVE_USER_RETURN_NOTIFIER
 
 config OUTPUT_FORMAT
         string
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index d27d0a2fec4c..375c917c37d2 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_AUDIT       7       /* syscall auditing active */
 #define TIF_SECCOMP             8       /* secure computing */
 #define TIF_MCE_NOTIFY          10      /* notify userspace of an MCE */
+#define TIF_USER_RETURN_NOTIFY  11      /* notify kernel of userspace return */
 #define TIF_NOTSC               16      /* TSC is not accessible in userland */
 #define TIF_IA32                17      /* 32bit process */
 #define TIF_FORK                18      /* ret_from_fork */
@@ -107,6 +108,7 @@ struct thread_info {
 #define _TIF_SYSCALL_AUDIT      (1 << TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP            (1 << TIF_SECCOMP)
 #define _TIF_MCE_NOTIFY         (1 << TIF_MCE_NOTIFY)
+#define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY)
 #define _TIF_NOTSC              (1 << TIF_NOTSC)
 #define _TIF_IA32               (1 << TIF_IA32)
 #define _TIF_FORK               (1 << TIF_FORK)
@@ -142,13 +144,14 @@ struct thread_info {
 
 /* Only used for 64 bit */
 #define _TIF_DO_NOTIFY_MASK                                             \
-        (_TIF_SIGPENDING|_TIF_MCE_NOTIFY|_TIF_NOTIFY_RESUME)
+        (_TIF_SIGPENDING | _TIF_MCE_NOTIFY | _TIF_NOTIFY_RESUME |       \
+         _TIF_USER_RETURN_NOTIFY)
 
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW                                                 \
         (_TIF_IO_BITMAP|_TIF_DEBUGCTLMSR|_TIF_DS_AREA_MSR|_TIF_NOTSC)
 
-#define _TIF_WORK_CTXSW_PREV _TIF_WORK_CTXSW
+#define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY)
 #define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW|_TIF_DEBUG)
 
 #define PREEMPT_ACTIVE          0x10000000
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 5284cd2b5776..e51b056fc88f 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -9,6 +9,7 @@
 #include <linux/pm.h>
 #include <linux/clockchips.h>
 #include <linux/random.h>
+#include <linux/user-return-notifier.h>
 #include <trace/events/power.h>
 #include <asm/system.h>
 #include <asm/apic.h>
@@ -224,6 +225,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
                  */
                 memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
         }
+        propagate_user_return_notify(prev_p, next_p);
 }
 
 int sys_fork(struct pt_regs *regs)
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 6a44a76055ad..c49f90f7957a 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -19,6 +19,7 @@
 #include <linux/stddef.h>
 #include <linux/personality.h>
 #include <linux/uaccess.h>
+#include <linux/user-return-notifier.h>
 
 #include <asm/processor.h>
 #include <asm/ucontext.h>
@@ -872,6 +873,8 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
                 if (current->replacement_session_keyring)
                         key_replace_session_keyring();
         }
+        if (thread_info_flags & _TIF_USER_RETURN_NOTIFY)
+                fire_user_return_notifiers();
 
 #ifdef CONFIG_X86_32
         clear_thread_flag(TIF_IRET);
diff --git a/include/linux/user-return-notifier.h b/include/linux/user-return-notifier.h
new file mode 100644
index 000000000000..b6ac056291d7
--- /dev/null
+++ b/include/linux/user-return-notifier.h
@@ -0,0 +1,42 @@
+#ifndef _LINUX_USER_RETURN_NOTIFIER_H
+#define _LINUX_USER_RETURN_NOTIFIER_H
+
+#ifdef CONFIG_USER_RETURN_NOTIFIER
+
+#include <linux/list.h>
+#include <linux/sched.h>
+
+struct user_return_notifier {
+        void (*on_user_return)(struct user_return_notifier *urn);
+        struct hlist_node link;
+};
+
+
+void user_return_notifier_register(struct user_return_notifier *urn);
+void user_return_notifier_unregister(struct user_return_notifier *urn);
+
+static inline void propagate_user_return_notify(struct task_struct *prev,
+                                                struct task_struct *next)
+{
+        if (test_tsk_thread_flag(prev, TIF_USER_RETURN_NOTIFY)) {
+                clear_tsk_thread_flag(prev, TIF_USER_RETURN_NOTIFY);
+                set_tsk_thread_flag(next, TIF_USER_RETURN_NOTIFY);
+        }
+}
+
+void fire_user_return_notifiers(void);
+
+#else
+
+struct user_return_notifier {};
+
+static inline void propagate_user_return_notify(struct task_struct *prev,
+                                                struct task_struct *next)
+{
+}
+
+static inline void fire_user_return_notifiers(void) {}
+
+#endif
+
+#endif
diff --git a/kernel/user-return-notifier.c b/kernel/user-return-notifier.c
new file mode 100644
index 000000000000..530ccb816513
--- /dev/null
+++ b/kernel/user-return-notifier.c
@@ -0,0 +1,46 @@
+
+#include <linux/user-return-notifier.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+
+static DEFINE_PER_CPU(struct hlist_head, return_notifier_list);
+
+#define URN_LIST_HEAD per_cpu(return_notifier_list, raw_smp_processor_id())
+
+/*
+ * Request a notification when the current cpu returns to userspace.  Must be
+ * called in atomic context.  The notifier will also be called in atomic
+ * context.
+ */
+void user_return_notifier_register(struct user_return_notifier *urn)
+{
+        set_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
+        hlist_add_head(&urn->link, &URN_LIST_HEAD);
+}
+EXPORT_SYMBOL_GPL(user_return_notifier_register);
+
+/*
+ * Removes a registered user return notifier.  Must be called from atomic
+ * context, and from the same cpu registration occured in.
+ */
+void user_return_notifier_unregister(struct user_return_notifier *urn)
+{
+        hlist_del(&urn->link);
+        if (hlist_empty(&URN_LIST_HEAD))
+                clear_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
+}
+EXPORT_SYMBOL_GPL(user_return_notifier_unregister);
+
+/* Calls registered user return notifiers */
+void fire_user_return_notifiers(void)
+{
+        struct user_return_notifier *urn;
+        struct hlist_node *tmp1, *tmp2;
+        struct hlist_head *head;
+
+        head = &get_cpu_var(return_notifier_list);
+        hlist_for_each_entry_safe(urn, tmp1, tmp2, head, link)
+                urn->on_user_return(urn);
+        put_cpu_var();
+}