linux-kernel - Re: [PATCH v2 01/17] mm/gup: Fixup p*_access

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CA+55aFz3yvU=kVmwGdvVgTrG4UW24Eg19VNCbV9Umwqr8262mw@mail.gmail.com>
Date:   Fri, 15 Dec 2017 17:05:54 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Andy Lutomirsky <luto@...nel.org>,
        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 <linux-mm@...ck.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 01/17] mm/gup: Fixup p*_access_permitted()

On Fri, Dec 15, 2017 at 4:31 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>>
>> The fact is, if we have non-user mappings in the user part of the
>> address space, we _need_ to teach access_ok() about them, because
>> fundamentally any "get_user()/put_user()" will happily ignore the lack
>> of PAGE_USER (since those happen from kernel space).
>
> Details, please - how *can* access_ok() be taught of that?

We'd have to do something like put the !PAGE_USER mapping at the top
of the user address space, and then simply make user_addr_max()
smaller than the actual user page table size.

Or some other silly hack.

I do not believe there is any sane way to have !PAGE_USER in
_general_, if you actually want to limit access to it.

(We _could_ use !PAGE_USER for things that aren't really strictly
about security - ie  we could have used it for the NUMA balancing
instead of using the P bit, and just let put_user/get_user blow
through them).

             Linus