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 00:35:34 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Christoph Hellwig <hch@...radead.org>,
        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>,
        Arnd Bergmann <arnd@...db.de>,
        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 08:27:47AM +0100, Al Viro wrote:
> And you *still* do the same.  Christoph, this is ridiculous - the worst
> part of the area is not a couple of functions in fs/read_write.c, it's
> a fucking lot of ->read() and ->write() instances in shitty driver code,
> pardon the redundance.  And _that_ is still done under set_fs(KERNEL_DS).

For now yes.  But it provides a sane API on top, and then we can
start moving the drivers that matter to the iter variants and drop
support for the rest soon.  Most in-kernel I/O is done to files, and
the rest to a very limited set of devices. (not accounting for sockets
through their own APIs, thats another story)

> That's what I'm objecting to.  Centralized kernel_readv() et.al. - sure,
> and fs/read_write.c is the right place for those.  No arguments here.
> Conversion to those - absolutely; drivers have no fucking business touching
> set_fs() at all.  But your primitives are trouble waiting to happen.
> Let them take kvec arrays.  And let them, in case when there's no
> ->read_iter()/->write_iter(), do set_fs().  Statically, without this
> if (iter->type & ITER_KVEC) ... stuff.

Oh weĺl.  I can do that first, but I think eventually we'll have to
get back to what I've done now.