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

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Date:   Wed, 10 May 2017 17:18:33 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, Greg KH <greg@...ah.com>,
        Thomas Garnier <thgarnie@...gle.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Howells <dhowells@...hat.com>,
        René Nyffenegger <mail@...enyffenegger.ch>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode

On Wed, May 10, 2017 at 1:14 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Wed, May 10, 2017 at 09:08:41AM +0100, Al Viro wrote:
>> On Wed, May 10, 2017 at 09:37:04AM +0200, Arnd Bergmann wrote:
>>
>> > > How about trying to remove all of them?  If we could actually get rid
>> > > of all of them, we could drop the arch support, and we'd get faster,
>> > > simpler, shorter uaccess code throughout the kernel.
>>
>> BTW, not all get_user() under KERNEL_DS are plain loads.  There is an
>> exception - probe_kernel_read().
>
> And various calls that looks like opencoded versions, e.g. drivers/dio
> or the ELF loader.
>
> But in the long run we'll just need a separate primitive for that,
> but that can wait until the set_fs calls outside the core code are
> gone.

I suspect that, on most arches, the primitive is called
__copy_from_user().  We could make the generic code do that except
where overridden.