From: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
To: Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
Catalin Marinas <Catalin.Marinas@arm.com>
Cc: nd <nd@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-kselftest@vger.kernel.org"
<linux-kselftest@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Will Deacon <Will.Deacon@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v4 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt
Date: Thu, 13 Jun 2019 15:32:42 +0000 [thread overview]
Message-ID: <ba822b33-a822-02ef-9b85-725f4353596a@arm.com> (raw)
In-Reply-To: <5963d144-be9b-78d8-9130-ef92bc66b1fd@arm.com>
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.
next prev parent reply other threads:[~2019-06-13 15:32 UTC|newest]
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 [this message]
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
2019-06-13 15:51 ` [PATCH v5 2/2] arm64: Relax Documentation/arm64/tagged-pointers.txt Vincenzo Frascino
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