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

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Message-ID: <20170512081154.GQ390@ZenIV.linux.org.uk>
Date: Fri, 12 May 2017 09:11:54 +0100
From: Al Viro <viro@...IV.linux.org.uk>
To: Arnd Bergmann <arnd@...db.de>
Cc: Ingo Molnar <mingo@...nel.org>, Andy Lutomirski <luto@...nel.org>,
	Christoph Hellwig <hch@...radead.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>,
	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: Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode

On Fri, May 12, 2017 at 09:43:40AM +0200, Arnd Bergmann wrote:

> How realistic and how useful would it be to first completely eliminate
> the ones that are in loadable modules and then wrapping the definition
> in #ifndef MODULE (or even make it an extern function)?

Eliminate _what_?  ->read() and ->write() instances?

> This should be a fairly complete list of the modular users:
> 
> drivers/block/drbd/drbd_main.c: set_fs(KERNEL_DS);

Ah, set_fs()...  Sure, many of those can be killed off.  Wouldn't be
a bad idea, but I don't understand what difference does modular/built-in
make here...

This one: AFAICS doesn't give a damn about set_fs() at all.

> drivers/input/serio/hp_sdc.c:   set_fs(KERNEL_DS);

Open-coded probe_kernel_read(), apparently.

> drivers/media/v4l2-core/v4l2-compat-ioctl32.c:          set_fs(KERNEL_DS);

massive compat ioctl crap.

> drivers/misc/lkdtm_bugs.c:      set_fs(KERNEL_DS);

insane.

> drivers/s390/crypto/pkey_api.c: set_fs(KERNEL_DS);

No idea.

> drivers/staging/comedi/drivers/serial2002.c:    set_fs(KERNEL_DS);

Open-coded kernel_write(); to some character device, no less...  And similar
for kernel_read(), apparently.

> drivers/staging/lustre/lnet/libcfs/tracefile.c: set_fs(get_ds());

Fuck knows; kernel_write() might do it.  Depends upon what it's writing
to.

You've missed other places in lustre, BTW - including the ioctls on
sockets, etc.

> drivers/staging/media/atomisp/pci/atomisp2/atomisp_compat_ioctl32.c:
>  set_fs(KERNEL_DS);

Compat ioctl crap, again.

> drivers/staging/rtl8723bs/os_dep/osdep_service.c:               oldfs
> = get_fs(); set_fs(get_ds());

Oh, lovely - reading an arbitrary (as in, specified by pathname) file.
Firmware (mis)handling?

> drivers/usb/gadget/function/f_mass_storage.c:   set_fs(get_ds());

No idea.

> drivers/usb/gadget/function/u_uac1.c:   set_fs(KERNEL_DS);

kernel_write(), by the look of it.  Or something similar.

> drivers/vhost/vhost.c:  set_fs(USER_DS);

kernel thread doing use_mm()

> drivers/video/fbdev/core/fbmem.c:       set_fs(KERNEL_DS);

compat ioctl.

> drivers/video/fbdev/hpfb.c:     set_fs(KERNEL_DS);

probe_kernel_read()

> fs/autofs4/waitq.c:     set_fs(KERNEL_DS);

kernel_write()

> fs/binfmt_aout.c:       set_fs(KERNEL_DS);
> fs/binfmt_elf.c:                set_fs(USER_DS);
> fs/binfmt_elf_fdpic.c:  set_fs(KERNEL_DS);

coredump stuff.

> fs/btrfs/send.c:        set_fs(KERNEL_DS);
kernel_write()

Anyway, what's special about modules?  IDGI...
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