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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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

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