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

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Mon, Feb 12, 2018 at 8:54 AM, Andrew Cooper
<andrew.cooper3@xxxxxxxxxx> 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 :(
>

+1, this used to be an issue under vmx as well

Tamas

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