From: robin.murphy@arm.com (Robin Murphy)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] arm64: add alignment fault hanling
Date: Tue, 16 Feb 2016 10:57:49 +0000 [thread overview]
Message-ID: <56C300AD.8070505@arm.com> (raw)
In-Reply-To: <20160216103104.GC14509@arm.com>
On 16/02/16 10:31, Will Deacon wrote:
> On Tue, Feb 16, 2016 at 04:44:35AM +0000, EunTaik Lee wrote:
>> Userspace memory is mapped as below:
>> F2A7F000--F2A7FFFF Normal Memory
>> F2A80000--F2A80FFF Device nGnRnE
>>
>> And that userspace application makes a system call
>> as below:
>>
>> -009 |do_strncpy_from_user(inline)
>> -009 |strncpy_from_user()
>> -010 |getname_flags()
>> -011 |user_path_at_empty()
>> -012 |user_path_at()
>> -013 |SYSC_faccessat(inline)
>> -013 |sys_faccessat()
>> -014 |__sys_trace(asm)
>> --> |exception
>>
>> The string spans from 0xF2A7FFC1 to 0xF2A7FFFB.
>>
>> When do_strncpy_from_user() reads the last (unsigned long)
>> value, the alignement fault is triggered. The 8 byte
>> from 0xF2A7FFC1 spans to the next page that is mapped as
>> Device nGnRnE, which does not allow an unaligned access,
>> causes the abort.
>>
>> The instruction which caused the alignment fault is registered
>> in the fixup table but the exception handler does not reach there.
>>
>> This patch registers a alignment fault handler and fixes up the
>> pc if appropriate.
>
> As discussed with Catalin previously, we should solve this by adding a
> guard page rather than handling the fault.
...especially since we may not even get a fault. See "Crossing a page
boundary with different memory types or Shareability attributes" in the
UNPREDICTABLE spec (K1.2.10 in the latest ARMv8 ARM).
Robin.
>
> Will
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
next prev parent reply other threads:[~2016-02-16 10:57 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-16 4:44 [PATCH v2] arm64: add alignment fault hanling EunTaik Lee
2016-02-16 10:31 ` Will Deacon
2016-02-16 10:57 ` Robin Murphy [this message]
2016-02-16 12:21 ` Catalin Marinas
2016-02-16 16:00 ` Will Deacon
2016-02-16 17:04 ` Will Deacon
2016-02-16 18:50 ` Linus Torvalds
2016-02-16 21:31 ` Arjan van de Ven
2016-02-16 23:04 ` Catalin Marinas
[not found] ` <CA+55aFz+ttJoEG_WkpkwV=+Wunzxpj9NoHobq-8oFZS0HEEyeA@mail.gmail.com>
2016-02-17 0:28 ` Linus Torvalds
2016-02-19 18:14 ` Catalin Marinas
2016-02-19 22:09 ` Linus Torvalds
2016-02-16 17:09 ` Catalin Marinas
2016-02-16 17:11 ` Catalin Marinas
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