On Wed, Aug 31, 2016 at 8:30 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:
> 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);
>
>
> Oh, I remember why I didn't do it also (except header changes):
> uprobes uses &special_mapping_vmops in inserted XOL area.
>
That's fine. I think you should check *both* vm_ops and
vm_private_data to avoid (unlikely) confusion with some other VMA.
--Andy
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