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

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Date: Thu, 6 Jul 2017 22:48:46 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Thomas Garnier <thgarnie@...gle.com>
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, 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?

Thanks,

	tglx

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