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

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Date:   Fri, 12 May 2017 08:57:33 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Martin Schwidefsky <schwidefsky@...ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Garnier <thgarnie@...gle.com>, Greg KH <greg@...ah.com>,
        Daniel Micay <danielmicay@...il.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>,
        Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        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>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode


* Kees Cook <keescook@...omium.org> wrote:

> > git commit b5a882fcf146c87cb6b67c6df353e1c042b8773d
> > "s390: restore address space when returning to user space".
> 
> If I'm understanding this, it won't catch corruption of addr_limit
> during fast-path syscalls, though (i.e. addr_limit changed without a
> call to set_fs()). :(

Nor does it, or the patch you propose, protect against against something 
corrupting task->mm pointer, or the task->*uid values, or any of the myriads of 
security relevant values stored in the task structure!

Making sure API (set_fs()) usage is bug-free and protecting against the effects of 
general data corruption are two unrelated things that should not mixed.

Thanks,

	Ingo