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

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Date:   Wed, 31 Aug 2016 18:30:47 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     Andy Lutomirski <luto@...capital.net>
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 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.

-- 
              Dmitry