vdso/timens: Refactor copy-pasted find_timens_vvar_page() helper into one copy

find_timens_vvar_page() is not architecture-specific, as can be seen from
how all five per-architecture versions of it are the same.

(arm64, powerpc and riscv are exactly the same; x86 and s390 have two
characters difference inside a comment, less blank lines, and mark the
!CONFIG_TIME_NS version as inline.)

Refactor the five copies into a central copy in kernel/time/namespace.c.

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20221130115320.2918447-1-jannh@google.com

arch/arm64/kernel/vdso.c

@@ -151,28 +151,6 @@ int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
 	mmap_read_unlock(mm);
 	return 0;
 }
-
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops.
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-#else
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
-}
 #endif
 
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

arch/powerpc/kernel/vdso.c

@@ -129,28 +129,6 @@ int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
 
 	return 0;
 }
-
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops.
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-#else
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
-}
 #endif
 
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

arch/riscv/kernel/vdso.c

@@ -137,28 +137,6 @@ int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
 	mmap_read_unlock(mm);
 	return 0;
 }
-
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops.
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-#else
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
-}
 #endif
 
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

arch/s390/kernel/vdso.c

@@ -44,21 +44,6 @@ struct vdso_data *arch_get_vdso_data(void *vvar_page)
 	return (struct vdso_data *)(vvar_page);
 }
 
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops().
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-	WARN(1, "vvar_page accessed remotely");
-	return NULL;
-}
-
 /*
  * The VVAR page layout depends on whether a task belongs to the root or
  * non-root time namespace. Whenever a task changes its namespace, the VVAR
@@ -84,11 +69,6 @@ int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
 	mmap_read_unlock(mm);
 	return 0;
 }
-#else
-static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
-}
 #endif
 
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

arch/x86/entry/vdso/vma.c

@@ -98,24 +98,6 @@ static int vdso_mremap(const struct vm_special_mapping *sm,
 }
 
 #ifdef CONFIG_TIME_NS
-static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	if (likely(vma->vm_mm == current->mm))
-		return current->nsproxy->time_ns->vvar_page;
-
-	/*
-	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
-	 * through interfaces like /proc/$pid/mem or
-	 * process_vm_{readv,writev}() as long as there's no .access()
-	 * in special_mapping_vmops().
-	 * For more details check_vma_flags() and __access_remote_vm()
-	 */
-
-	WARN(1, "vvar_page accessed remotely");
-
-	return NULL;
-}
-
 /*
  * The vvar page layout depends on whether a task belongs to the root or
  * non-root time namespace. Whenever a task changes its namespace, the VVAR
@@ -140,11 +122,6 @@ int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
 
 	return 0;
 }
-#else
-static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
-{
-	return NULL;
-}
 #endif
 
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,

include/linux/time_namespace.h

@@ -45,6 +45,7 @@ struct time_namespace *copy_time_ns(unsigned long flags,
 void free_time_ns(struct time_namespace *ns);
 void timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk);
 struct vdso_data *arch_get_vdso_data(void *vvar_page);
+struct page *find_timens_vvar_page(struct vm_area_struct *vma);
 
 static inline void put_time_ns(struct time_namespace *ns)
 {
@@ -141,6 +142,11 @@ static inline void timens_on_fork(struct nsproxy *nsproxy,
 	return;
 }
 
+static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
+{
+	return NULL;
+}
+
 static inline void timens_add_monotonic(struct timespec64 *ts) { }
 static inline void timens_add_boottime(struct timespec64 *ts) { }
 

kernel/time/namespace.c

@@ -192,6 +192,24 @@ static void timens_setup_vdso_data(struct vdso_data *vdata,
 	offset[CLOCK_BOOTTIME_ALARM]	= boottime;
 }
 
+struct page *find_timens_vvar_page(struct vm_area_struct *vma)
+{
+	if (likely(vma->vm_mm == current->mm))
+		return current->nsproxy->time_ns->vvar_page;
+
+	/*
+	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
+	 * through interfaces like /proc/$pid/mem or
+	 * process_vm_{readv,writev}() as long as there's no .access()
+	 * in special_mapping_vmops().
+	 * For more details check_vma_flags() and __access_remote_vm()
+	 */
+
+	WARN(1, "vvar_page accessed remotely");
+
+	return NULL;
+}
+
 /*
  * Protects possibly multiple offsets writers racing each other
  * and tasks entering the namespace.