linux-kernel - Re: [PATCH v10 1/3] x86/syscalls: Check address limit on user-mode return

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Message-ID: <CAJcbSZGSqm8HYMv8biOQEWvan1nma3vjKNJ1mgMz52AyJ5adGA@mail.gmail.com>
Date:   Thu, 6 Jul 2017 13:52:24 -0700
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kees Cook <keescook@...omium.org>, 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>,
        Oleg Nesterov <oleg@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Petr Mladek <pmladek@...e.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Al Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Dave Hansen <dave.hansen@...el.com>,
        David Howells <dhowells@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Pratyush Anand <panand@...hat.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v10 1/3] x86/syscalls: Check address limit on user-mode return

On Thu, Jul 6, 2017 at 1:48 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Thu, 6 Jul 2017, Thomas Garnier wrote:
>> On Wed, Jun 28, 2017 at 10:52 AM, Kees Cook <keescook@...omium.org> wrote:
>> >
>> > On Tue, Jun 20, 2017 at 1:24 PM, Kees Cook <keescook@...omium.org> wrote:
>> > > On Wed, Jun 14, 2017 at 6:12 PM, Thomas Garnier <thgarnie@...gle.com> wrote:
>> > >> Ensure the address limit is a user-mode segment before returning to
>> > >> user-mode. Otherwise a process can corrupt kernel-mode memory and elevate
>> > >> privileges [1].
>> > >>
>> > >> The set_fs function sets the TIF_SETFS flag to force a slow path on
>> > >> return. In the slow path, the address limit is checked to be USER_DS if
>> > >> needed.
>> > >>
>> > >> The addr_limit_user_check function is added as a cross-architecture
>> > >> function to check the address limit.
>> > >>
>> > >> [1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990
>> > >>
>> > >> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
>> > >
>> > > Thanks for reworking this series!
>> > >
>> > > The bad state correctly BUGs under the LKDTM test:
>> > >
>> > > [   21.171586] lkdtm: Performing direct entry CORRUPT_USER_DS
>> > > [   21.172791] lkdtm: setting bad task size limit
>> > > [   21.173742] ------------[ cut here ]------------
>> > > [   21.174641] kernel BUG at ./include/linux/syscalls.h:220!
>> > > ...
>> > > [   21.193166] Call Trace:
>> > > [   21.193617]  ? trace_hardirqs_on_thunk+0x1a/0x1c
>> > > [   21.194443]  entry_SYSCALL64_slow_path+0x25/0x25
>> > >
>> > >
>> > > Tested-by: Kees Cook <keescook@...omium.org>
>> >
>> > Is everyone happy with this patch for x86? Does this need anything
>> > more/different?
>>
>> Asking again. Additional feedback? Anyone wants to pick-it up?
>
> Can do. This needs to be a combo of all 3 I assume as the x86 one contains
> the function used by all of them, right?

That is correct.

>
> Thanks,
>
>         tglx



-- 
Thomas