linux-kernel - Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode

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Message-ID: <CAGXu5jKHVMRMKDfn+=kkbm+JkWPhoEtDwKx=QXAYxg1p9bn7PQ@mail.gmail.com>
Date:   Tue, 9 May 2017 09:50:32 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Greg KH <greg@...ah.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        linux-s390 <linux-s390@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        René Nyffenegger <mail@...enyffenegger.ch>,
        Catalin Marinas <catalin.marinas@....com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Rik van Riel <riel@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Brian Gerst <brgerst@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux API <linux-api@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        James Morse <james.morse@....com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode

On Tue, May 9, 2017 at 9:03 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Tue, May 09, 2017 at 06:02:50AM -0700, Christoph Hellwig wrote:
>> On Tue, May 09, 2017 at 06:00:01AM -0700, Andy Lutomirski wrote:
>> > fs/splice.c has some, ahem, interesting uses that have been the source
>> > of nasty exploits in the past.  Converting them to use iov_iter
>> > properly would be really, really nice.  Christoph, I don't suppose
>> > you'd like to do that?
>>
>> I can take care of all the fs code including this one.
>
> I spent the afternoon hacking up where I'd like this to head.  It's
> completely untested as of now:
>
>         http://git.infradead.org/users/hch/vfs.git/shortlog/refs/heads/setfs-elimination

Ooooh yes! Nice work.

I love this:
http://git.infradead.org/users/hch/vfs.git/commitdiff/51e83f50f824ca23f5584c172138e6b7c2ff786d
but I wonder what it'll cause out-of-tree code to do. I mean, I'd
rather nothing out-of-tree be calling these, but I'd hate 3rd party
hacks even more.

http://git.infradead.org/users/hch/vfs.git/commitdiff/018e0e9030777121fe87e89d43066691e7366587
This accidentally(?) removes the kernel-doc comments.

http://git.infradead.org/users/hch/vfs.git/commitdiff/78b62c730254fc39fa888cdbdca08fde6e09a798
Could this be made defensive? (Return 0 if ret wraps, for example?) I
see what the comment says, but not everyone will read that. :(

http://git.infradead.org/users/hch/vfs.git/commitdiff/a106276ca0294be054bc89ce97219933fe543df1
Perhaps unconditionally set USER_DS on exit instead of retaining
whatever was there?

-Kees

-- 
Kees Cook
Pixel Security