Re: [Xen-devel] [PATCH v3 2/4] hvm/svm: Enable Breakpoint events

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/02/18 16:10, Alexandru Stefan ISAILA wrote:
> On Lu, 2018-02-12 at 15:54 +0000, Andrew Cooper wrote:
>> On 12/02/18 15:08, Alexandru Isaila wrote:
>>> @@ -2619,14 +2634,31 @@ void svm_vmexit_handler(struct
>>> cpu_user_regs *regs)
>>>          break;
>>>
>>>      case VMEXIT_EXCEPTION_BP:
>>> -        if ( !v->domain->debugger_attached )
>>> -            goto unexpected_exit_type;
>>> -        /* AMD Vol2, 15.11: INT3, INTO, BOUND intercepts do not
>>> update RIP. */
>>> -        if ( (inst_len = __get_instruction_length(v, INSTR_INT3))
>>> == 0 )
>>> +        inst_len = __get_instruction_length(v, INSTR_INT3);
>> There are multiple ways of ending up with this vmexit, and INT3 is
>> not
>> the only way.
>>
>> The old code was somewhat broken (but only in the case that a
>> debugger
>> was attached), but now with  this introspection hook active,
>> executing
>> `0xcd 0x03` will end up crashing the domain because of a length
>> mismatch
>> looking for 0xcc.
>>
>> You need to inspect EXITINTINFO to work out what went on here, and
>> distinguish INT3 from INT $3.
>>
>> Can I suggest that you run this unit test
>> http://xenbits.xen.org/docs/xtf/test-swint-emulation.html under debug
>> introspection an check that you get all expected events?  Every time
>> we
>> touch this code, we seem to break it :(
>>
>> ~Andrew
>>
> I've tested on Intel and AMD and I only get events on int3. Further
> more, I don't think there is any way to use the vmcb->exitintinfo
> because all the fields are 0 on the time of VMEXIT_EXCEPTION_BP. Did I
> understand the test scenario correctly?

Quite possibly, but now I'm even more confused.  I'll have a quick play.

~Andrew

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