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From: Catalin Marinas <catalin.marinas@arm.com>
To: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
	Andrey Konovalov <andreyknvl@google.com>,
	Will Deacon <will.deacon@arm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-kselftest@vger.kernel.org,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v5 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt
Date: Fri, 21 Jun 2019 16:16:41 +0100
Message-ID: <20190621151640.GI18954@arrakis.emea.arm.com> (raw)
In-Reply-To: <1c55a610-9aa5-4675-f7de-79a1661a660d@arm.com>

On Tue, Jun 18, 2019 at 02:13:01PM +0100, Kevin Brodsky wrote:
> On 13/06/2019 16:51, Vincenzo Frascino wrote:
> > +The ARM64 Tagged Address ABI is an opt-in feature, and an application can
> > +control it using the following:
> > + - /proc/sys/abi/tagged_addr: a new sysctl interface that can be used to
> > +        prevent the applications from enabling the relaxed ABI.
> > +        The sysctl is meant also for testing purposes in order to provide a
> > +        simple way for the userspace to verify the return error checking of
> > +        the prctl() commands without having to reconfigure the kernel.
> > +        The sysctl supports the following configuration options:
> > +         - 0: Disable ARM64 Tagged Address ABI for all the applications.
> > +         - 1 (Default): Enable ARM64 Tagged Address ABI for all the
> > +                        applications.
> 
> I find this very confusing, because it suggests that the default value of
> PR_GET_TAGGED_ADDR_CTRL for new processes will be set to the value of this
> sysctl, when in fact this sysctl is about restricting the *availability* of
> the new ABI. Instead of disabling the ABI, I would talk about disabling
> access to the new ABI here.

This bullet point needs to be re-written. The sysctl is meant to disable
opting in to the ABI. I'd also drop the "meant for testing" part. I put
it in my commit log as justification but I don't think it should be part
of the ABI document.

> > + - prctl()s:
> > +  - PR_SET_TAGGED_ADDR_CTRL: can be used to enable or disable the Tagged
> > +        Address ABI.
> > +        The (unsigned int) arg2 argument is a bit mask describing the
> > +        control mode used:
> > +          - PR_TAGGED_ADDR_ENABLE: Enable ARM64 Tagged Address ABI.
> > +        The arguments arg3, arg4, and arg5 are ignored.
> 
> Have we definitely decided that arg{3,4,5} are ignored? Catalin?

I don't have a strong preference either way. If it's simpler for the
user to ignore them, fine by me. I can see in the current prctl commands
a mix if ignore vs forced zero.

> > +the ABI guarantees the following behaviours:
> > +
> > +  - Every current or newly introduced syscall can accept any valid tagged
> > +    pointers.
> "pointer". Also, is it really useful to talk about newly introduced syscall?
> New from which point of view?

I think we should drop this guarantee. It would have made sense if we
allowed tagged pointers everywhere but we already have some exceptions.

> > +3. ARM64 Tagged Address ABI Exceptions
> > +--------------------------------------
> > +
> > +The behaviours described in section 2, with particular reference to the
> > +acceptance by the syscalls of any valid tagged pointer are not applicable
> > +to the following cases:
> > +  - mmap() addr parameter.
> > +  - mremap() new_address parameter.
> > +  - prctl_set_mm() struct prctl_map fields.
> > +  - prctl_set_mm_map() struct prctl_map fields.
> 
> prctl_set_mm() and prctl_set_mm_map() are internal kernel functions, not
> syscall names. IIUC, we don't want to allow any address field settable via
> the PR_SET_MM prctl() to be tagged. Catalin, is that correct? I think this
> needs rephrasing.

I fully agree. It should talk about PR_SET_MM, PR_SET_MM_MAP,
PR_SET_MM_MAP_SIZE.

-- 
Catalin

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  reply index

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-12 11:43 [PATCH v17 00/15] arm64: untag user pointers passed to the kernel Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 01/15] arm64: untag user pointers in access_ok and __uaccess_mask_ptr Andrey Konovalov
2019-06-12 14:26   ` Vincenzo Frascino
2019-06-12 11:43 ` [PATCH v17 02/15] lib, arm64: untag user pointers in strn*_user Andrey Konovalov
2019-06-12 14:28   ` Vincenzo Frascino
2019-06-12 11:43 ` [PATCH v17 03/15] arm64: Introduce prctl() options to control the tagged user addresses ABI Andrey Konovalov
2019-06-12 14:30   ` Vincenzo Frascino
2019-06-12 14:55   ` Catalin Marinas
2019-06-13 11:02   ` Dave Martin
2019-06-13 15:26     ` Catalin Marinas
2019-06-14  5:13       ` Kees Cook
2019-06-18  9:18         ` Dave Martin
2019-06-13 11:16   ` Dave Martin
2019-06-13 15:35     ` Catalin Marinas
2019-06-13 15:45       ` Vincenzo Frascino
2019-06-13 15:57         ` Catalin Marinas
2019-06-13 16:15           ` Vincenzo Frascino
2019-06-17 13:56   ` Catalin Marinas
2019-06-17 16:56     ` Szabolcs Nagy
2019-06-17 16:57     ` Evgenii Stepanov
2019-06-17 17:18       ` Catalin Marinas
2019-06-17 21:59         ` Evgenii Stepanov
2019-06-19 14:45   ` Andrey Konovalov
2019-06-19 15:29     ` Catalin Marinas
2019-06-12 11:43 ` [PATCH v17 04/15] mm, arm64: untag user pointers passed to memory syscalls Andrey Konovalov
2019-06-12 14:31   ` Vincenzo Frascino
2019-06-19 15:55   ` Khalid Aziz
2019-06-19 16:46     ` Khalid Aziz
2019-06-24 14:22       ` Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 05/15] mm, arm64: untag user pointers in mm/gup.c Andrey Konovalov
2019-06-12 14:33   ` Vincenzo Frascino
2019-06-19 16:41   ` Khalid Aziz
2019-06-12 11:43 ` [PATCH v17 06/15] mm, arm64: untag user pointers in get_vaddr_frames Andrey Konovalov
2019-06-12 14:34   ` Vincenzo Frascino
2019-06-19 16:48   ` Khalid Aziz
2019-06-12 11:43 ` [PATCH v17 07/15] fs, arm64: untag user pointers in copy_mount_options Andrey Konovalov
2019-06-12 14:35   ` Vincenzo Frascino
2019-06-19 20:01   ` Khalid Aziz
2019-06-12 11:43 ` [PATCH v17 08/15] userfaultfd, arm64: untag user pointers Andrey Konovalov
2019-06-12 14:40   ` Vincenzo Frascino
2019-06-12 11:43 ` [PATCH v17 09/15] drm/amdgpu, " Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 10/15] drm/radeon, arm64: untag user pointers in radeon_gem_userptr_ioctl Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 11/15] IB/mlx4, arm64: untag user pointers in mlx4_get_umem_mr Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 12/15] media/v4l2-core, arm64: untag user pointers in videobuf_dma_contig_user_get Andrey Konovalov
2019-06-19 20:05   ` Khalid Aziz
2019-06-12 11:43 ` [PATCH v17 13/15] tee/shm, arm64: untag user pointers in tee_shm_register Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 14/15] vfio/type1, arm64: untag user pointers in vaddr_get_pfn Andrey Konovalov
2019-06-12 14:41   ` Vincenzo Frascino
2019-06-12 15:58   ` Auger Eric
2019-06-12 11:43 ` [PATCH v17 15/15] selftests, arm64: add a selftest for passing tagged pointers to kernel Andrey Konovalov
2019-06-12 12:30   ` Szabolcs Nagy
2019-06-12 15:00     ` Catalin Marinas
2019-06-19 14:42       ` Andrey Konovalov
2019-06-12 14:21 ` [PATCH v4 0/2] arm64 relaxed ABI Vincenzo Frascino
2019-06-12 14:21   ` [PATCH v4 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt Vincenzo Frascino
2019-06-12 15:35     ` Catalin Marinas
2019-06-13 10:15       ` Vincenzo Frascino
2019-06-13 11:37         ` Dave Martin
2019-06-13 12:28           ` Catalin Marinas
2019-06-13 13:23             ` Dave Martin
2019-06-13 15:39               ` Catalin Marinas
2019-06-12 16:30     ` Szabolcs Nagy
2019-06-13  9:20       ` Catalin Marinas
2019-06-13 10:14         ` Szabolcs Nagy
2019-06-13 11:16           ` Vincenzo Frascino
2019-06-13 12:28             ` Szabolcs Nagy
2019-06-13 14:03               ` Vincenzo Frascino
2019-06-13 15:32                 ` Szabolcs Nagy
2019-06-13 15:35                   ` Vincenzo Frascino
2019-06-12 14:21   ` [PATCH v4 2/2] arm64: Relax Documentation/arm64/tagged-pointers.txt Vincenzo Frascino
2019-06-12 15:56     ` Catalin Marinas
2019-06-12 16:37     ` Szabolcs Nagy
2019-06-13 15:51 ` [PATCH v5 0/2] arm64 relaxed ABI Vincenzo Frascino
2019-06-13 15:51   ` [PATCH v5 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt Vincenzo Frascino
2019-06-18 11:02     ` Szabolcs Nagy
2019-06-18 13:13     ` Kevin Brodsky
2019-06-21 15:16       ` Catalin Marinas [this message]
2019-06-13 15:51   ` [PATCH v5 2/2] arm64: Relax Documentation/arm64/tagged-pointers.txt Vincenzo Frascino

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