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Subject[tip: timers/core] x86/vdso: Handle faults on timens page
The following commit has been merged into the timers/core branch of tip:

Commit-ID: af34ebeb866fafc0a9a09dda51c52ccec007ace0
Gitweb: https://git.kernel.org/tip/af34ebeb866fafc0a9a09dda51c52ccec007ace0
Author: Dmitry Safonov <dima@arista.com>
AuthorDate: Tue, 12 Nov 2019 01:27:13
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 14 Jan 2020 12:20:58 +01:00

x86/vdso: Handle faults on timens page

If a task belongs to a time namespace then the VVAR page which contains
the system wide VDSO data is replaced with a namespace specific page
which has the same layout as the VVAR page.

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/20191112012724.250792-25-dima@arista.com


---
arch/x86/entry/vdso/vma.c | 54 ++++++++++++++++++++++++++++++++++++--
mm/mmap.c | 2 +-
2 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 04e3498..e5f3361 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -14,11 +14,14 @@
#include <linux/elf.h>
#include <linux/cpu.h>
#include <linux/ptrace.h>
+#include <linux/time_namespace.h>
+
#include <asm/pvclock.h>
#include <asm/vgtod.h>
#include <asm/proto.h>
#include <asm/vdso.h>
#include <asm/vvar.h>
+#include <asm/tlb.h>
#include <asm/page.h>
#include <asm/desc.h>
#include <asm/cpufeature.h>
@@ -107,10 +110,36 @@ static int vvar_mremap(const struct vm_special_mapping *sm,
return 0;
}

+#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;
+}
+#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,
struct vm_area_struct *vma, struct vm_fault *vmf)
{
const struct vdso_image *image = vma->vm_mm->context.vdso_image;
+ unsigned long pfn;
long sym_offset;

if (!image)
@@ -130,8 +159,21 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
return VM_FAULT_SIGBUS;

if (sym_offset == image->sym_vvar_page) {
- return vmf_insert_pfn(vma, vmf->address,
- __pa_symbol(&__vvar_page) >> PAGE_SHIFT);
+ struct page *timens_page = find_timens_vvar_page(vma);
+
+ pfn = __pa_symbol(&__vvar_page) >> PAGE_SHIFT;
+
+ /*
+ * If a task belongs to a time namespace then a namespace
+ * specific VVAR is mapped with the sym_vvar_page offset and
+ * the real VVAR page is mapped with the sym_timens_page
+ * offset.
+ * See also the comment near timens_setup_vdso_data().
+ */
+ if (timens_page)
+ pfn = page_to_pfn(timens_page);
+
+ return vmf_insert_pfn(vma, vmf->address, pfn);
} else if (sym_offset == image->sym_pvclock_page) {
struct pvclock_vsyscall_time_info *pvti =
pvclock_get_pvti_cpu0_va();
@@ -146,6 +188,14 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
if (tsc_pg && vclock_was_used(VCLOCK_HVCLOCK))
return vmf_insert_pfn(vma, vmf->address,
virt_to_phys(tsc_pg) >> PAGE_SHIFT);
+ } else if (sym_offset == image->sym_timens_page) {
+ struct page *timens_page = find_timens_vvar_page(vma);
+
+ if (!timens_page)
+ return VM_FAULT_SIGBUS;
+
+ pfn = __pa_symbol(&__vvar_page) >> PAGE_SHIFT;
+ return vmf_insert_pfn(vma, vmf->address, pfn);
}

return VM_FAULT_SIGBUS;
diff --git a/mm/mmap.c b/mm/mmap.c
index 9c64852..60c17d3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3342,6 +3342,8 @@ static const struct vm_operations_struct special_mapping_vmops = {
.fault = special_mapping_fault,
.mremap = special_mapping_mremap,
.name = special_mapping_name,
+ /* vDSO code relies that VVAR can't be accessed remotely */
+ .access = NULL,
};

static const struct vm_operations_struct legacy_special_mapping_vmops = {
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