x86/vdso: Zap vvar pages when switching to a time namespace

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
page tables are cleared and then they will be re-faulted with a
corresponding layout.

Co-developed-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20191112012724.250792-27-dima@arista.com

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index d2fd8a5..c1b8496 100644 (file)
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -51,6 +51,7 @@ void __init init_vdso_image(const struct vdso_image *image)
                                                image->alt_len));
 }
 
+static const struct vm_special_mapping vvar_mapping;
 struct linux_binprm;
 
 static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
@@ -128,6 +129,32 @@ static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
 
        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
+ * page tables are cleared and then they will re-faulted with a
+ * corresponding layout.
+ * See also the comment near timens_setup_vdso_data() for details.
+ */
+int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
+{
+       struct mm_struct *mm = task->mm;
+       struct vm_area_struct *vma;
+
+       if (down_write_killable(&mm->mmap_sem))
+               return -EINTR;
+
+       for (vma = mm->mmap; vma; vma = vma->vm_next) {
+               unsigned long size = vma->vm_end - vma->vm_start;
+
+               if (vma_is_special_mapping(vma, &vvar_mapping))
+                       zap_page_range(vma, vma->vm_start, size);
+       }
+
+       up_write(&mm->mmap_sem);
+       return 0;
+}
 #else
 static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
 {

diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index 6b7767f..04a2ba8 100644 (file)
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -31,6 +31,9 @@ struct time_namespace {
 extern struct time_namespace init_time_ns;
 
 #ifdef CONFIG_TIME_NS
+extern int vdso_join_timens(struct task_struct *task,
+                           struct time_namespace *ns);
+
 static inline struct time_namespace *get_time_ns(struct time_namespace *ns)
 {
        kref_get(&ns->kref);
@@ -77,6 +80,12 @@ static inline ktime_t timens_ktime_to_host(clockid_t clockid, ktime_t tim)
 }
 
 #else
+static inline int vdso_join_timens(struct task_struct *task,
+                                  struct time_namespace *ns)
+{
+       return 0;
+}
+
 static inline struct time_namespace *get_time_ns(struct time_namespace *ns)
 {
        return NULL;

diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index d705c15..0732964 100644 (file)
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -281,6 +281,7 @@ static void timens_put(struct ns_common *ns)
 static int timens_install(struct nsproxy *nsproxy, struct ns_common *new)
 {
        struct time_namespace *ns = to_time_ns(new);
+       int err;
 
        if (!current_is_single_threaded())
                return -EUSERS;
@@ -291,6 +292,10 @@ static int timens_install(struct nsproxy *nsproxy, struct ns_common *new)
 
        timens_set_vvar_page(current, ns);
 
+       err = vdso_join_timens(current, ns);
+       if (err)
+               return err;
+
        get_time_ns(ns);
        put_time_ns(nsproxy->time_ns);
        nsproxy->time_ns = ns;
@@ -305,6 +310,7 @@ int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk)
 {
        struct ns_common *nsc = &nsproxy->time_ns_for_children->ns;
        struct time_namespace *ns = to_time_ns(nsc);
+       int err;
 
        /* create_new_namespaces() already incremented the ref counter */
        if (nsproxy->time_ns == nsproxy->time_ns_for_children)
@@ -312,6 +318,10 @@ int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk)
 
        timens_set_vvar_page(tsk, ns);
 
+       err = vdso_join_timens(tsk, ns);
+       if (err)
+               return err;
+
        get_time_ns(ns);
        put_time_ns(nsproxy->time_ns);
        nsproxy->time_ns = ns;