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From: Kees Cook <keescook@chromium.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: enh <enh@google.com>, Evgenii Stepanov <eugenis@google.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Khalid Aziz <khalid.aziz@oracle.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-rdma@vger.kernel.org, linux-media@vger.kernel.org,
	kvm@vger.kernel.org,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Yishai Hadas <yishaih@mellanox.com>,
	Felix Kuehling <Felix.Kuehling@amd.com>,
	Alexander Deucher <Alexander.Deucher@amd.com>,
	Christian Koenig <Christian.Koenig@amd.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Jens Wiklander <jens.wiklander@linaro.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Leon Romanovsky <leon@kernel.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	Kostya Serebryany <kcc@google.com>, Lee Smith <Lee.Smith@arm.com>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
	Jacob Bramley <Jacob.Bramley@arm.com>,
	Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	Dave Martin <Dave.Martin@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel
Date: Sat, 1 Jun 2019 22:06:10 -0700
Message-ID: <201906012156.55E2C45@keescook> (raw)
In-Reply-To: <20190528170244.GF32006@arrakis.emea.arm.com>

On Tue, May 28, 2019 at 06:02:45PM +0100, Catalin Marinas wrote:
> On Thu, May 23, 2019 at 02:31:16PM -0700, Kees Cook wrote:
> > syzkaller already attempts to randomly inject non-canonical and
> > 0xFFFF....FFFF addresses for user pointers in syscalls in an effort to
> > find bugs like CVE-2017-5123 where waitid() via unchecked put_user() was
> > able to write directly to kernel memory[1].
> > 
> > It seems that using TBI by default and not allowing a switch back to
> > "normal" ABI without a reboot actually means that userspace cannot inject
> > kernel pointers into syscalls any more, since they'll get universally
> > stripped now. Is my understanding correct, here? i.e. exploiting
> > CVE-2017-5123 would be impossible under TBI?
> > 
> > If so, then I think we should commit to the TBI ABI and have a boot
> > flag to disable it, but NOT have a process flag, as that would allow
> > attackers to bypass the masking. The only flag should be "TBI or MTE".
> > 
> > If so, can I get top byte masking for other architectures too? Like,
> > just to strip high bits off userspace addresses? ;)
> 
> Just for fun, hack/attempt at your idea which should not interfere with
> TBI. Only briefly tested on arm64 (and the s390 __TYPE_IS_PTR macro is
> pretty weird ;)):

OMG, this is amazing and bonkers. I love it.

> --------------------------8<---------------------------------
> diff --git a/arch/s390/include/asm/compat.h b/arch/s390/include/asm/compat.h
> index 63b46e30b2c3..338455a74eff 100644
> --- a/arch/s390/include/asm/compat.h
> +++ b/arch/s390/include/asm/compat.h
> @@ -11,9 +11,6 @@
>  
>  #include <asm-generic/compat.h>
>  
> -#define __TYPE_IS_PTR(t) (!__builtin_types_compatible_p( \
> -				typeof(0?(__force t)0:0ULL), u64))
> -
>  #define __SC_DELOUSE(t,v) ({ \
>  	BUILD_BUG_ON(sizeof(t) > 4 && !__TYPE_IS_PTR(t)); \
>  	(__force t)(__TYPE_IS_PTR(t) ? ((v) & 0x7fffffff) : (v)); \
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index e2870fe1be5b..b1b9fe8502da 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -119,8 +119,15 @@ struct io_uring_params;
>  #define __TYPE_IS_L(t)	(__TYPE_AS(t, 0L))
>  #define __TYPE_IS_UL(t)	(__TYPE_AS(t, 0UL))
>  #define __TYPE_IS_LL(t) (__TYPE_AS(t, 0LL) || __TYPE_AS(t, 0ULL))
> +#define __TYPE_IS_PTR(t) (!__builtin_types_compatible_p(typeof(0 ? (__force t)0 : 0ULL), u64))
>  #define __SC_LONG(t, a) __typeof(__builtin_choose_expr(__TYPE_IS_LL(t), 0LL, 0L)) a
> +#ifdef CONFIG_64BIT
> +#define __SC_CAST(t, a)	(__TYPE_IS_PTR(t) \
> +				? (__force t) ((__u64)a & ~(1UL << 55)) \
> +				: (__force t) a)
> +#else
>  #define __SC_CAST(t, a)	(__force t) a
> +#endif
>  #define __SC_ARGS(t, a)	a
>  #define __SC_TEST(t, a) (void)BUILD_BUG_ON_ZERO(!__TYPE_IS_LL(t) && sizeof(t) > sizeof(long))

I'm laughing, I'm crying. Now I have to go look at the disassembly to
see how this actually looks. (I mean, it _does_ solve my specific case
of the waitid() flaw, but wouldn't help with pointers deeper in structs,
etc, though TBI does, I think still help with that. I have to catch back
up on the thread...) Anyway, if it's not too expensive it'd block
reachability for those kinds of flaws.

I wonder what my chances are of actually getting this landed? :)
(Though, I guess I need to find a "VA width" macro instead of a raw 55.)

Thanks for thinking of __SC_CAST() and __TYPE_IS_PTR() together. Really
made my day. :)

-- 
Kees Cook

  reply index

Thread overview: 99+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-06 16:30 Andrey Konovalov
2019-05-06 16:30 ` [PATCH v15 01/17] uaccess: add untagged_addr definition for other arches Andrey Konovalov
2019-05-29 14:49   ` Khalid Aziz
2019-05-06 16:30 ` [PATCH v15 02/17] arm64: untag user pointers in access_ok and __uaccess_mask_ptr Andrey Konovalov
2019-05-06 16:30 ` [PATCH v15 03/17] lib, arm64: untag user pointers in strn*_user Andrey Konovalov
2019-05-22 10:41   ` Catalin Marinas
2019-05-06 16:30 ` [PATCH v15 04/17] mm: add ksys_ wrappers to memory syscalls Andrey Konovalov
2019-05-22 10:56   ` Catalin Marinas
2019-05-06 16:30 ` [PATCH v15 05/17] arms64: untag user pointers passed " Andrey Konovalov
2019-05-22 11:49   ` Catalin Marinas
2019-05-22 21:16     ` Evgenii Stepanov
2019-05-23  9:04       ` Catalin Marinas
2019-05-24  4:23         ` Evgenii Stepanov
2019-05-24 15:41   ` Andrew Murray
2019-05-25  9:57   ` Catalin Marinas
2019-05-27  9:42   ` Catalin Marinas
2019-05-27 14:37   ` Catalin Marinas
2019-05-28 14:54     ` Andrew Murray
2019-05-28 15:40       ` Catalin Marinas
2019-05-28 15:56         ` Dave Martin
2019-05-28 16:34           ` Catalin Marinas
2019-05-29 12:42             ` Dave Martin
2019-05-29 13:23               ` Catalin Marinas
2019-05-29 15:18                 ` Dave Martin
2019-05-28 23:33         ` Khalid Aziz
2019-05-29 14:20           ` Catalin Marinas
2019-05-29 19:16             ` Khalid Aziz
2019-05-30 15:11               ` Catalin Marinas
2019-05-30 16:05                 ` Khalid Aziz
2019-05-30 16:57                   ` Catalin Marinas
2019-05-28 13:05   ` Catalin Marinas
2019-05-06 16:30 ` [PATCH v15 06/17] mm: untag user pointers in do_pages_move Andrey Konovalov
2019-05-22 11:51   ` Catalin Marinas
2019-05-06 16:30 ` [PATCH v15 07/17] mm, arm64: untag user pointers in mm/gup.c Andrey Konovalov
2019-05-22 11:56   ` Catalin Marinas
2019-05-06 16:30 ` [PATCH v15 08/17] mm, arm64: untag user pointers in get_vaddr_frames Andrey Konovalov
2019-05-06 16:30 ` [PATCH v15 09/17] fs, arm64: untag user pointers in copy_mount_options Andrey Konovalov
2019-05-22 12:09   ` Catalin Marinas
2019-05-06 16:30 ` [PATCH v15 10/17] fs, arm64: untag user pointers in fs/userfaultfd.c Andrey Konovalov
2019-05-06 16:30 ` [PATCH v15 11/17] drm/amdgpu, arm64: untag user pointers Andrey Konovalov
2019-05-07 16:43   ` Kuehling, Felix
2019-05-06 16:30 ` [PATCH v15 12/17] drm/radeon, arm64: untag user pointers in radeon_gem_userptr_ioctl Andrey Konovalov
2019-05-07 16:44   ` Kuehling, Felix
2019-05-06 16:30 ` [PATCH v15 13/17] IB, arm64: untag user pointers in ib_uverbs_(re)reg_mr() Andrey Konovalov
2019-05-06 19:50   ` Jason Gunthorpe
2019-05-07  6:33     ` Leon Romanovsky
2019-05-06 16:31 ` [PATCH v15 14/17] media/v4l2-core, arm64: untag user pointers in videobuf_dma_contig_user_get Andrey Konovalov
2019-05-24 13:13   ` Mauro Carvalho Chehab
2019-05-06 16:31 ` [PATCH v15 15/17] tee, arm64: untag user pointers in tee_shm_register Andrey Konovalov
2019-05-06 16:31 ` [PATCH v15 16/17] vfio/type1, arm64: untag user pointers in vaddr_get_pfn Andrey Konovalov
2019-05-06 16:31 ` [PATCH v15 17/17] selftests, arm64: add a selftest for passing tagged pointers to kernel Andrey Konovalov
2019-05-22 14:16   ` Catalin Marinas
2019-05-31 14:21     ` Andrey Konovalov
2019-05-31 16:22       ` Catalin Marinas
2019-05-17 14:49 ` [PATCH v15 00/17] arm64: untag user pointers passed to the kernel Catalin Marinas
2019-05-20 23:53   ` Evgenii Stepanov
2019-05-21 18:29     ` Catalin Marinas
2019-05-22  0:04       ` Kees Cook
2019-05-22 10:11         ` Catalin Marinas
2019-05-22 15:30           ` enh
2019-05-22 16:35             ` Catalin Marinas
2019-05-22 16:58               ` enh
2019-05-23 15:21                 ` Catalin Marinas
2019-05-22 20:47               ` Kees Cook
2019-05-22 23:03                 ` Evgenii Stepanov
2019-05-22 23:09                   ` enh
2019-05-23  7:34                     ` Catalin Marinas
2019-05-23 14:44                 ` Catalin Marinas
2019-05-23 15:44                   ` enh
2019-05-23 17:00                     ` Catalin Marinas
2019-05-23 16:38                   ` Kees Cook
2019-05-23 17:43                     ` Catalin Marinas
2019-05-23 21:31                       ` Kees Cook
2019-05-24 11:20                         ` Catalin Marinas
2019-05-28 17:02                         ` Catalin Marinas
2019-06-02  5:06                           ` Kees Cook [this message]
2019-05-22 19:21             ` Kees Cook
2019-05-22 20:15               ` enh
2019-05-23 15:08               ` Catalin Marinas
2019-05-23 17:51         ` Khalid Aziz
2019-05-23 20:11           ` Catalin Marinas
2019-05-23 21:42             ` Khalid Aziz
2019-05-23 21:49             ` Khalid Aziz
2019-05-24 10:11               ` Catalin Marinas
2019-05-24 14:25                 ` Khalid Aziz
2019-05-28 14:14                   ` Andrey Konovalov
2019-05-29  6:11                     ` Christoph Hellwig
2019-05-29 12:12                       ` Catalin Marinas
2019-05-30 17:15                     ` Catalin Marinas
2019-05-31 14:29                       ` Andrey Konovalov
2019-05-31 16:19                         ` Catalin Marinas
2019-05-31 16:24                           ` Andrey Konovalov
2019-05-31 16:46                             ` Catalin Marinas
2019-05-21 18:48   ` Jason Gunthorpe
2019-05-22 13:49     ` Dave Martin
2019-05-23  0:20       ` Jason Gunthorpe
2019-05-23 10:42         ` Dave Martin
2019-05-23 16:57           ` Catalin Marinas
2019-05-24 14:23             ` Dave Martin

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