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From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
	Catalin Marinas <Catalin.Marinas@arm.com>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-doc@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-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"linux-kselftest@vger.kernel.org"
	<linux-kselftest@vger.kernel.org>, nd <nd@arm.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v4 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt
Date: Thu, 13 Jun 2019 16:35:35 +0100
Message-ID: <a05a2dfb-3398-455d-8586-b79dfb7a772f@arm.com> (raw)
In-Reply-To: <ba822b33-a822-02ef-9b85-725f4353596a@arm.com>


On 13/06/2019 16:32, Szabolcs Nagy wrote:
> On 13/06/2019 15:03, Vincenzo Frascino wrote:
>> On 13/06/2019 13:28, Szabolcs Nagy wrote:
>>> On 13/06/2019 12:16, Vincenzo Frascino wrote:
>>>> On 13/06/2019 11:14, Szabolcs Nagy wrote:
>>>>> On 13/06/2019 10:20, Catalin Marinas wrote:
>>>>>> On Wed, Jun 12, 2019 at 05:30:34PM +0100, Szabolcs Nagy wrote:
>>>>>>> On 12/06/2019 15:21, Vincenzo Frascino wrote:
>>>>>>>> +  - a mapping below sbrk(0) done by the process itself
>>>>>>>
>>>>>>> doesn't the mmap rule cover this?
>>>>>>
>>>>>> IIUC it doesn't cover it as that's memory mapped by the kernel
>>>>>> automatically on access vs a pointer returned by mmap(). The statement
>>>>>> above talks about how the address is obtained by the user.
>>>>>
>>>>> ok i read 'mapping below sbrk' as an mmap (possibly MAP_FIXED)
>>>>> that happens to be below the heap area.
>>>>>
>>>>> i think "below sbrk(0)" is not the best term to use: there
>>>>> may be address range below the heap area that can be mmapped
>>>>> and thus below sbrk(0) and sbrk is a posix api not a linux
>>>>> syscall, the libc can implement it with mmap or whatever.
>>>>>
>>>>> i'm not sure what the right term for 'heap area' is
>>>>> (the address range between syscall(__NR_brk,0) at
>>>>> program startup and its current value?)
>>>>>
>>>>
>>>> I used sbrk(0) with the meaning of "end of the process's data segment" not
>>>> implying that this is a syscall, but just as a useful way to identify the mapping.
>>>> I agree that it is a posix function implemented by libc but when it is used with
>>>> 0 finds the current location of the program break, which can be changed by brk()
>>>> and depending on the new address passed to this syscall can have the effect of
>>>> allocating or deallocating memory.
>>>>
>>>> Will changing sbrk(0) with "end of the process's data segment" make it more clear?
>>>
>>> i don't understand what's the relevance of the *end*
>>> of the data segment.
>>>
>>> i'd expect the text to say something about the address
>>> range of the data segment.
>>>
>>> i can do
>>>
>>> mmap((void*)65536, 65536, PROT_READ|PROT_WRITE, MAP_FIXED|MAP_SHARED|MAP_ANON, -1, 0);
>>>
>>> and it will be below the end of the data segment.
>>>
>>
>> As far as I understand the data segment "lives" below the program break, hence
>> it is a way of describing the range from which the user can obtain a valid
>> tagged pointer.>
>> Said that, I am not really sure on how do you want me to document this (my aim
>> is for this to be clear to the userspace developers). Could you please propose
>> something?
> 
> [...], it is in the memory ranges privately owned by a
> userspace process and it is obtained in one of the
> following ways:
> 
> - mmap done by the process itself, [...]
> 
> - brk syscall done by the process itself.
>   (i.e. the heap area between the initial location
>   of the program break at process creation and its
>   current location.)
> 
> - any memory mapped by the kernel [...]
> 
> the data segment that's part of the process image is
> already covered by the last point.
> 

Thanks Szabolcs, I will update the document accordingly.

-- 
Regards,
Vincenzo

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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 [this message]
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
2019-06-13 15:51   ` [PATCH v5 2/2] arm64: Relax Documentation/arm64/tagged-pointers.txt Vincenzo Frascino

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