linux-kernel - Re: [PATCHv3 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO

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Message-ID: <CALCETrWLPbbXXMa+1hMg1hduF60sB_+MnBXMvyVMPUepWc1PpQ@mail.gmail.com>
Date:   Wed, 31 Aug 2016 08:42:52 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>, X86 ML <x86@...nel.org>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Pavel Emelyanov <xemul@...tuozzo.com>
Subject: Re: [PATCHv3 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO_*

On Wed, Aug 31, 2016 at 8:30 AM, Dmitry Safonov <dsafonov@...tuozzo.com> wrote:
> On 08/31/2016 06:00 PM, Andy Lutomirski wrote:
>>
>> On Fri, Aug 26, 2016 at 10:13 AM, Dmitry Safonov <dsafonov@...tuozzo.com>
>> 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@...nel.org>
>>> Cc: Oleg Nesterov <oleg@...hat.com>
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> Cc: "H. Peter Anvin" <hpa@...or.com>
>>> Cc: Ingo Molnar <mingo@...hat.com>
>>> Cc: linux-mm@...ck.org
>>> Cc: x86@...nel.org
>>> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
>>> Cc: Pavel Emelyanov <xemul@...tuozzo.com>
>>> Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
>>> ---
>>>  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