[PATCHv8 26/34] x86/vdso: Zap vvar pages on switch a time namspace

Dmitry Safonov
2019-11-12T01:27:15Z

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.

Co-developed-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
arch/x86/entry/vdso/vma.c | 27 +++++++++++++++++++++++++++
include/linux/time_namespace.h | 9 +++++++++
kernel/time/namespace.c | 10 ++++++++++
3 files changed, 46 insertions(+)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index d6cb8a16f368..57ada3e95f8d 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -50,6 +50,7 @@ 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,
@@ -127,6 +128,32 @@ 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 cdb438ba0037..f1cdd3a6f842 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -30,6 +30,9 @@ 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);
@@ -74,6 +77,12 @@ 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 e14cd1ca387d..0dc0742ed1ee 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -280,6 +280,7 @@ 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;
@@ -290,6 +291,10 @@ 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;
@@ -304,6 +309,7 @@ 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)
@@ -311,6 +317,10 @@ 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;
--
2.24.0