Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples

Jin, Yao
2020-08-11T08:31:18Z

Hi Peter,

On 8/11/2020 3:59 PM, Peter Zijlstra wrote:
> On Tue, Aug 11, 2020 at 03:50:43PM +0800, Jin, Yao wrote:
>> Could I post v2 which basically refers to your patch but removes some
>> conditions since I see some issues in test if we use these conditions.
>>
>> 1. Remove '!event->attr.exclude_hv || !event->attr.exclude_host ||
>> !event->attr.exclude_guest' at the entry of sanitize_sample_regs().
>>
>> 2. Remove '!attr.exclude_hv || !attr.exclude_host || !attr.exclude_guest'
>> at the perf_event_open syscall entry.
>
> exclude_host, maybe -- due to the dodgy semantics of it, but the others
> should definitely be there.
>

exclude_guest and exclude_hv are tricky too.

If we do 'perf record -e cycles:u' in both host and guest, we can see:

event->attr.exclude_guest = 0

thus sanitize_sample_regs() returns regs directly even if exclude_kernel = 1.

And in guest, exclude_hv = 0, it's out of my expectation too.

Thanks
Jin Yao