[llvm-commits] [PATCH] improve ARM halt encoding

[JF Bastien]

For debuggers? Or for process termination?

It definitely is significant for NaCl.


On Wed, Jan 16, 2013 at 2:39 PM, Jim Grosbach <grosbach at apple.com> wrote:

> The entire encoding is semantically significant on Darwin. I suspect
> that's true on other platforms, too, but I don't know for sure.
>
> -Jim
>
> On Jan 16, 2013, at 2:20 PM, JF Bastien <jfb at chromium.org> wrote:
>
> We've defined a few other instructions in a similar manner, see:
>
> http://src.chromium.org/viewvc/native_client/trunk/src/native_client/src/include/arm_sandbox.h?content-type=text%2Fplain<http://src.chromium.org/viewvc/native_client/trunk/src/native_client/src/include/arm_sandbox.h?content-type=text/plain>
>
> Abort now is indeed a single instruction that shouldn't occur often, but
> the others should. The goal is to progressively upstream PNaCl changes.
>
> Other code that uses the instruction presumably only detects UDF, and not
> the immediate? Or is your concern that the actual immediate is what is
> looked at?
>
>
> On Wed, Jan 16, 2013 at 2:13 PM, Jim Grosbach <grosbach at apple.com> wrote:
>
>> Hi JF,
>>
>> There is a lot of extant code that uses the current values and has for
>> quite a long time. Changing has pretty extreme ripple effects, to put it
>> mildly.
>>
>> Given the circumstances for when the compiler will use a TRAP
>> instruction, I'm pretty skeptical of any real-world security benefits to
>> this. Can you elaborate?
>>
>> -Jim
>>
>> On Jan 16, 2013, at 12:46 PM, JF Bastien <jfb at chromium.org> wrote:
>>
>> > I've attached a patch from PNaCl with changes the ARM halt encoding so
>> that it also looks like a halt in Thumb. This can catch bugs when executing
>> ARM code as Thumb, whether it be in the context of compiler/JIT bugs, or an
>> attacker trying to get validated ARM code to execute as Thumb (which is a
>> concern for PNaCl).
>> >
>> > Note that the instruction itself isn't changing (it's still UDF), only
>> the immediate.
>> > <arm-halt.diff>_______________________________________________
>> > llvm-commits mailing list
>> > llvm-commits at cs.uiuc.edu
>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>
>>
>
>
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