From: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
To: Vincenzo Frascino <Vincenzo.Frascino@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 12:28:08 +0000 [thread overview]
Message-ID: <8e3c9537-de10-0d0d-f5bb-c33bde92443f@arm.com> (raw)
In-Reply-To: <6ebbda37-5dd9-d0d5-d9cb-286c7a5b7f8e@arm.com>
On 13/06/2019 12:16, Vincenzo Frascino wrote:
> Hi Szabolcs,
>
> thank you for your review.
>
> On 13/06/2019 11:14, Szabolcs Nagy wrote:
>> On 13/06/2019 10:20, Catalin Marinas wrote:
>>> Hi Szabolcs,
>>>
>>> On Wed, Jun 12, 2019 at 05:30:34PM +0100, Szabolcs Nagy wrote:
>>>> On 12/06/2019 15:21, Vincenzo Frascino wrote:
>>>>> +2. ARM64 Tagged Address ABI
>>>>> +---------------------------
>>>>> +
>>>>> +From the kernel syscall interface prospective, we define, for the purposes
>>>> ^^^^^^^^^^^
>>>> perspective
>>>>
>>>>> +of this document, a "valid tagged pointer" as a pointer that either it has
>>>>> +a zero value set in the top byte or it has a non-zero value, it is in memory
>>>>> +ranges privately owned by a userspace process and it is obtained in one of
>>>>> +the following ways:
>>>>> + - mmap() done by the process itself, where either:
>>>>> + * flags = MAP_PRIVATE | MAP_ANONYMOUS
>>>>> + * flags = MAP_PRIVATE and the file descriptor refers to a regular
>>>>> + file or "/dev/zero"
>>>>
>>>> this does not make it clear if MAP_FIXED or other flags are valid
>>>> (there are many map flags i don't know, but at least fixed should work
>>>> and stack/growsdown. i'd expect anything that's not incompatible with
>>>> private|anon to work).
>>>
>>> Just to clarify, this document tries to define the memory ranges from
>>> where tagged addresses can be passed into the kernel in the context
>>> of TBI only (not MTE); that is for hwasan support. FIXED or GROWSDOWN
>>> should not affect this.
>>
>> yes, so either the text should list MAP_* flags that don't affect
>> the pointer tagging semantics or specify private|anon mapping
>> with different wording.
>>
>
> Good point. Could you please propose a wording that would be suitable for this case?
i don't know all the MAP_ magic, but i think it's enough to change
the "flags =" to
* flags have MAP_PRIVATE and MAP_ANONYMOUS set or
* flags have MAP_PRIVATE set and the file descriptor refers to...
>>>>> + - 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.
>
> I will add what you are suggesting about the heap area.
>
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next prev parent reply other threads:[~2019-06-13 12:28 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 [this message]
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
2019-06-13 15:51 ` [PATCH v5 2/2] arm64: Relax Documentation/arm64/tagged-pointers.txt Vincenzo Frascino
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