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: <20170511112234.g4qmekxmq676pas6@pd.tnic>
Date:   Thu, 11 May 2017 13:22:34 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>
Cc:     Christoph Hellwig <hch@...radead.org>,
        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>,
        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 09, 2017 at 04:31:00PM -0700, Kees Cook wrote:
> > I don't like silent fixups.  If we want to do this, we should BUG or
> > at least WARN, not just change the addr limit.  But I'm also not
> > convinced it's indicative of an actual bug here.
> 
> Nothing should enter that function with KERNEL_DS set, right?
> 
> BUG_ON(get_fs() != USER_DS);

We're feeling triggerhappy, aren't we? A nice juicy WARN-splat along
with a fixup looks much better than killing the box, to me.

-- 
Regards/Gruss,
    Boris.

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