Re: [PATCHv3 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO_*

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On 08/31/2016 06:00 PM, Andy Lutomirski wrote:
On Fri, Aug 26, 2016 at 10:13 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:
Add API to change vdso blob type with arch_prctl.
As this is usefull only by needs of CRIU, expose
this interface under CONFIG_CHECKPOINT_RESTORE.

Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: x86@xxxxxxxxxx
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
---
 arch/x86/entry/vdso/vma.c         | 45 ++++++++++++++++++++++++++++++---------
 arch/x86/include/asm/vdso.h       |  2 ++
 arch/x86/include/uapi/asm/prctl.h |  6 ++++++
 arch/x86/kernel/process_64.c      | 25 ++++++++++++++++++++++
 4 files changed, 68 insertions(+), 10 deletions(-)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 5bcb25a9e573..dad2b2d8ff03 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -176,6 +176,16 @@ static int vvar_fault(const struct vm_special_mapping *sm,
        return VM_FAULT_SIGBUS;
 }

+static const struct vm_special_mapping vdso_mapping = {
+       .name = "[vdso]",
+       .fault = vdso_fault,
+       .mremap = vdso_mremap,
+};
+static const struct vm_special_mapping vvar_mapping = {
+       .name = "[vvar]",
+       .fault = vvar_fault,
+};
+
 /*
  * Add vdso and vvar mappings to current process.
  * @image          - blob to map
@@ -188,16 +198,6 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
        unsigned long text_start;
        int ret = 0;

-       static const struct vm_special_mapping vdso_mapping = {
-               .name = "[vdso]",
-               .fault = vdso_fault,
-               .mremap = vdso_mremap,
-       };
-       static const struct vm_special_mapping vvar_mapping = {
-               .name = "[vvar]",
-               .fault = vvar_fault,
-       };
-
        if (down_write_killable(&mm->mmap_sem))
                return -EINTR;

@@ -256,6 +256,31 @@ static int map_vdso_randomized(const struct vdso_image *image)
        return map_vdso(image, addr);
 }

+int map_vdso_once(const struct vdso_image *image, unsigned long addr)
+{
+       struct mm_struct *mm = current->mm;
+       struct vm_area_struct *vma;
+
+       down_write(&mm->mmap_sem);
+       /*
+        * Check if we have already mapped vdso blob - fail to prevent
+        * abusing from userspace install_speciall_mapping, which may
+        * not do accounting and rlimit right.
+        * We could search vma near context.vdso, but it's a slowpath,
+        * so let's explicitely check all VMAs to be completely sure.
+        */
+       for (vma = mm->mmap; vma; vma = vma->vm_next) {
+               if (vma->vm_private_data == &vdso_mapping ||
+                               vma->vm_private_data == &vvar_mapping) {

Should probably also check that vm_ops == &special_mapping_vmops,
which means that maybe there should be a:

static inline bool vma_is_special_mapping(const struct vm_area_struct
*vma, const struct vm_special_mapping &sm);

Well, yep, I thought about it, but left without it to not touch
additional headers.
Will do for the next version, thanks!

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