linux-kernel - Re: [PATCHv3 12/27] x86/vdso: Restrict splitting VVAR VMA

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Date:   Thu, 25 Apr 2019 19:46:48 +0100
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Jann Horn <jannh@...gle.com>, Dmitry Safonov <dima@...sta.com>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        Adrian Reber <adrian@...as.de>,
        Andrei Vagin <avagin@...nvz.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jeff Dike <jdike@...toit.com>, Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        containers@...ts.linux-foundation.org, criu@...nvz.org,
        Linux API <linux-api@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCHv3 12/27] x86/vdso: Restrict splitting VVAR VMA



On 4/25/19 7:41 PM, Jann Horn wrote:
> On Thu, Apr 25, 2019 at 6:17 PM Dmitry Safonov <dima@...sta.com> wrote:
>> Although, time namespace can work with VVAR VMA split, it seems worth
>> to forbid splitting VVAR resulting in stricter ABI and reducing amount
>> of corner-cases to consider while working further on VDSO.
> [...]
>> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
>> index babc4e7a519c..ff9875a4d53b 100644
>> --- a/arch/x86/entry/vdso/vma.c
>> +++ b/arch/x86/entry/vdso/vma.c
> [...]
>> +static int vvar_mremap(const struct vm_special_mapping *sm,
>> +               struct vm_area_struct *new_vma)
>> +{
>> +       unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
>> +       const struct vdso_image *image = current->mm->context.vdso_image;
> 
> Using current->mm in here is a bit awkward. So far the ->mremap
> handler can only be invoked for `current`, but still, maybe
> new_vma->vm_mm would be better here?

Yep, can do - also in vdso_mremap().
Though, it should be only stylistic as it's checked in
special_mapping_mremap() to be the same.

> 
>> +       if (new_size != -image->sym_vvar_start)
>> +               return -EINVAL;
>> +
>> +       return 0;
>> +}
> [...]
> 

Thanks,
          Dima