kallsyms: Add in_gate_area_no_task()

Add in_gate_area_no_task() for use in places where no task is valid
(e.g. kallsyms).  If you have a valid task, use in_gate_area() as
before.
Signed-off-by: Keith Owens <kaos@ocs.com.au>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

arch/x86_64/mm/init.c

@@ -623,3 +623,13 @@ int in_gate_area(struct task_struct *task, unsigned long addr)
 	struct vm_area_struct *vma = get_gate_vma(task);
 	return (addr >= vma->vm_start) && (addr < vma->vm_end);
 }
+
+/* Use this when you have no reliable task/vma, typically from interrupt
+ * context.  It is less reliable than using the task's vma and may give
+ * false positives.
+ */
+int in_gate_area_no_task(unsigned long addr)
+{
+	return ((addr >= VSYSCALL_START) && (addr < VSYSCALL_END) ||
+		(addr >= VSYSCALL32_BASE) && (addr < VSYSCALL32_END));
+}

include/linux/mm.h

@@ -800,7 +800,13 @@ kernel_map_pages(struct page *page, int numpages, int enable)
 #endif
 
 extern struct vm_area_struct *get_gate_vma(struct task_struct *tsk);
+#ifdef	__HAVE_ARCH_GATE_AREA
+int in_gate_area_no_task(unsigned long addr);
 int in_gate_area(struct task_struct *task, unsigned long addr);
+#else
+int in_gate_area_no_task(unsigned long addr);
+#define in_gate_area(task, addr) ({(void)task; in_gate_area_no_task(addr);})
+#endif	/* __HAVE_ARCH_GATE_AREA */
 
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */

mm/memory.c

@@ -1837,7 +1837,7 @@ struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
 #endif
 }
 
-int in_gate_area(struct task_struct *task, unsigned long addr)
+int in_gate_area_no_task(unsigned long addr)
 {
 #ifdef AT_SYSINFO_EHDR
 	if ((addr >= FIXADDR_USER_START) && (addr < FIXADDR_USER_END))