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Re: [PATCH v2] arm64: add alignment fault hanling

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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.

Will

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[PATCH v2] arm64: add alignment fault hanling EunTaik Lee <eun.taik.lee@samsung.com> - 2016-02-16 05:50 +0100
  Re: [PATCH v2] arm64: add alignment fault hanling Will Deacon <will.deacon@arm.com> - 2016-02-16 11:40 +0100
    Re: [PATCH v2] arm64: add alignment fault hanling Robin Murphy <robin.murphy@arm.com> - 2016-02-16 12:00 +0100
      Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-16 13:30 +0100
        Re: [PATCH v2] arm64: add alignment fault hanling Will Deacon <will.deacon@arm.com> - 2016-02-16 17:10 +0100
          Re: [PATCH v2] arm64: add alignment fault hanling Will Deacon <will.deacon@arm.com> - 2016-02-16 18:10 +0100
            Re: [PATCH v2] arm64: add alignment fault hanling Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-16 20:00 +0100
              Re: [PATCH v2] arm64: add alignment fault hanling Arjan van de Ven <arjan@linux.intel.com> - 2016-02-16 22:40 +0100
                Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-17 00:10 +0100
                Re: [PATCH v2] arm64: add alignment fault hanling Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-17 01:30 +0100
              Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-19 19:20 +0100
                Re: [PATCH v2] arm64: add alignment fault hanling Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-19 23:10 +0100
          Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-16 18:20 +0100
  Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-16 18:20 +0100

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