linux-kernel - Re: [PATCH v2 02/17] mm: Exempt special mappings from mlock(), mprotect() and madvise()

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Date:   Tue, 2 Jan 2018 16:44:22 +0000
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Will Deacon <will.deacon@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>, crml <criu@...nvz.org>
Subject: Re: [PATCH v2 02/17] mm: Exempt special mappings from mlock(),
 mprotect() and madvise()

Hi, sorry for the late reply,

2017-12-14 17:36 GMT+00:00 Peter Zijlstra <peterz@...radead.org>:
> On Thu, Dec 14, 2017 at 08:19:36AM -0800, Andy Lutomirski wrote:
>> On Thu, Dec 14, 2017 at 3:27 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>> > It makes no sense to ever prod at special mappings with any of these
>> > syscalls.
>> >
>> > XXX should we include munmap() ?
>>
>> This is an ABI break for the vdso.  Maybe that's okay, but mremap() on
>> the vdso is certainly used, and I can imagine debuggers using
>> mprotect().
>
> *groan*, ok so mremap() will actually still work after this, but yes,
> mprotect() will not. I hadn't figured people would muck with the VDSO
> like that.

mremap() is needed for CRIU, at least.

Please, don't restrict munmap(), as ARCH_MAP_VDSO_* allows to map vdso
iff it's not already mapped.
We don't need +w vdso mapping, but I guess that may break gdb breakpoints
on vdso.

Also, AFAICS, vma_is_special_mapping() has two parameters in linux-next,
and your patches set doesn't change that.

Thanks,
             Dmitry