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From: Dave Martin <Dave.Martin@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	kvm@vger.kernel.org, Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
	Will Deacon <will.deacon@arm.com>,
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	Leon Romanovsky <leon@kernel.org>,
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	Dmitry Vyukov <dvyukov@google.com>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
	Evgeniy Stepanov <eugenis@google.com>,
	linux-media@vger.kernel.org, Kees Cook <keescook@chromium.org>,
	Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
	Andrey Konovalov <andreyknvl@google.com>,
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	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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	linux-kernel@vger.kernel.org,
	Jens Wiklander <jens.wiklander@linaro.org>,
	Lee Smith <Lee.Smith@arm.com>,
	Alexander Deucher <Alexander.Deucher@amd.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Christian Koenig <Christian.Koenig@amd.com>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel
Date: Fri, 24 May 2019 15:23:54 +0100
Message-ID: <20190524142352.GY28398@e103592.cambridge.arm.com> (raw)
In-Reply-To: <20190523165708.q6ru7xg45aqfjzpr@mbp>

On Thu, May 23, 2019 at 05:57:09PM +0100, Catalin Marinas wrote:
> On Thu, May 23, 2019 at 11:42:57AM +0100, Dave P Martin wrote:
> > On Wed, May 22, 2019 at 09:20:52PM -0300, Jason Gunthorpe wrote:
> > > On Wed, May 22, 2019 at 02:49:28PM +0100, Dave Martin wrote:
> > > > If multiple people will care about this, perhaps we should try to
> > > > annotate types more explicitly in SYSCALL_DEFINEx() and ABI data
> > > > structures.
> > > > 
> > > > For example, we could have a couple of mutually exclusive modifiers
> > > > 
> > > > T __object *
> > > > T __vaddr * (or U __vaddr)
> > > > 
> > > > In the first case the pointer points to an object (in the C sense)
> > > > that the call may dereference but not use for any other purpose.
> > > 
> > > How would you use these two differently?
> > > 
> > > So far the kernel has worked that __user should tag any pointer that
> > > is from userspace and then you can't do anything with it until you
> > > transform it into a kernel something
> > 
> > Ultimately it would be good to disallow casting __object pointers execpt
> > to compatible __object pointer types, and to make get_user etc. demand
> > __object.
> > 
> > __vaddr pointers / addresses would be freely castable, but not to
> > __object and so would not be dereferenceable even indirectly.
> 
> I think it gets too complicated and there are ambiguous cases that we
> may not be able to distinguish. For example copy_from_user() may be used
> to copy a user data structure into the kernel, hence __object would
> work, while the same function may be used to copy opaque data to a file,
> so __vaddr may be a better option (unless I misunderstood your
> proposal).

Can you illustrate?  I'm not sure of your point here.

> We currently have T __user * and I think it's a good starting point. The
> prior attempt [1] was shut down because it was just hiding the cast
> using __force. We'd need to work through those cases again and rather
> start changing the function prototypes to avoid unnecessary casting in
> the callers (e.g. get_user_pages(void __user *) or come up with a new
> type) while changing the explicit casting to a macro where it needs to
> be obvious that we are converting a user pointer, potentially typed
> (tagged), to an untyped address range. We may need a user_ptr_to_ulong()
> macro or similar (it seems that we have a u64_to_user_ptr, wasn't aware
> of it).
> 
> It may actually not be far from what you suggested but I'd keep the
> current T __user * to denote possible dereference.

This may not have been clear, but __object and __vaddr would be
orthogonal to __user.  Since __object and __vaddr strictly constrain
what can be done with an lvalue, they could be cast on, but not be
cast off without __force.

Syscall arguments and pointer in ioctl structs etc. would typically
be annotated as __object __user * or __vaddr __user *.  Plain old
__user * would work as before, but would be more permissive and give
static analysers less information to go on.

Conversion or use or __object or __vaddr pointers would require specific
APIs in the kernel, so that we can be clear about the semantics.

Doing things this way would allow migration to annotation of most or all
ABI pointers with __object or __vaddr over time, but we wouldn't have to
do it all in one go.  Problem cases (which won't be the majority) could
continue to be plain __user.


This does not magically solve the challenges of MTE, but might provide
tools that are useful to help avoid bitrot and regressions over time.

I agree though that there might be a fair number of of cases that don't
conveniently fall under __object or __vaddr semantics.  It's hard to
know without trying it.

_Most_ syscall arguments seem to be fairly obviously one or another
though, and this approach has some possibility of scaling to ioctls
and other odd interfaces.

Cheers
---Dave

      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
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 [this message]

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