domain_crash_sync vs "plain crash"

domain_crash_sync vs "plain crash"

[Charles Gonçalves]

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When I'm performing some hypercalls with some "unexpected" parameters
(robustness test) sometimes the guest is explicitly  "killed" by xen
calling the domain_crash(), but sometimes the guest just crash without any
explicit message on dmesg or logs.

Are those "plain crashes" an expected behavior by design on Xen or are they
some untreated parameter checking or something else?

Can someone comment about it?

Thanks!


-- 
Atenciosamente,
Charles F.'. Gonçalves

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Re: domain_crash_sync vs "plain crash"

[Jan Beulich]

>>> On 07.05.18 at 03:06, <charles.fg@gmail.com> wrote:
> When I'm performing some hypercalls with some "unexpected" parameters
> (robustness test) sometimes the guest is explicitly  "killed" by xen
> calling the domain_crash(), but sometimes the guest just crash without any
> explicit message on dmesg or logs.
> 
> Are those "plain crashes" an expected behavior by design on Xen or are they
> some untreated parameter checking or something else?

A silent crash is never supposed to happen, but you always need to first
consider whether the crashing component actually has a way to get
something out to wherever you monitor its logs. That is, without (physical
or virtual, depending on component) serial console you're often unlikely to
actually observe any messages connected to the crash.

If you can track down a _truly_ silent crash to its origin, submitting a patch
to make it non-silent would be appreciated.

Jan



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Re: domain_crash_sync vs "plain crash"

[Andrew Cooper]

On 07/05/2018 08:09, Jan Beulich wrote:
>>>> On 07.05.18 at 03:06, <charles.fg@gmail.com> wrote:
>> When I'm performing some hypercalls with some "unexpected" parameters
>> (robustness test) sometimes the guest is explicitly  "killed" by xen
>> calling the domain_crash(), but sometimes the guest just crash without any
>> explicit message on dmesg or logs.
>>
>> Are those "plain crashes" an expected behavior by design on Xen or are they
>> some untreated parameter checking or something else?
> A silent crash is never supposed to happen, but you always need to first
> consider whether the crashing component actually has a way to get
> something out to wherever you monitor its logs. That is, without (physical
> or virtual, depending on component) serial console you're often unlikely to
> actually observe any messages connected to the crash.
>
> If you can track down a _truly_ silent crash to its origin, submitting a patch
> to make it non-silent would be appreciated.

Alternatively, if you are fuzzing the hypercalls, which it sounds like
you are, then you need to ensure that you blacklist operations such as
SCHEDOP_shutdown and SCHEDOP_poll to avoid the fuzzer hitting legitimate
hypercalls which shut down or block for indefinite periods of time.

~Andrew

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Re: domain_crash_sync vs "plain crash"

[Charles Gonçalves]

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"That is, without (physical
or virtual, depending on component) serial console you're often unlikely to
actually observe any messages connected to the crash."

I do not have any experience with serial console interaction on linux.
Can you list some examples for both cases (virtual| physical), I'll glad to
fully report any suspicious problem.

Thanks!

-- 
Atenciosamente,
Charles F.'. Gonçalves

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Re: domain_crash_sync vs "plain crash"

[Charles Gonçalves]

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@Andrew,

Despite SCHED_OP, that I've blacklisted, which one came to mind?


On Mon, May 7, 2018 at 5:13 AM Andrew Cooper <andrew.cooper3@citrix.com>
wrote:

> On 07/05/2018 08:09, Jan Beulich wrote:
> >>>> On 07.05.18 at 03:06, <charles.fg@gmail.com> wrote:
> >> When I'm performing some hypercalls with some "unexpected" parameters
> >> (robustness test) sometimes the guest is explicitly  "killed" by xen
> >> calling the domain_crash(), but sometimes the guest just crash without
> any
> >> explicit message on dmesg or logs.
> >>
> >> Are those "plain crashes" an expected behavior by design on Xen or are
> they
> >> some untreated parameter checking or something else?
> > A silent crash is never supposed to happen, but you always need to first
> > consider whether the crashing component actually has a way to get
> > something out to wherever you monitor its logs. That is, without
> (physical
> > or virtual, depending on component) serial console you're often unlikely
> to
> > actually observe any messages connected to the crash.
> >
> > If you can track down a _truly_ silent crash to its origin, submitting a
> patch
> > to make it non-silent would be appreciated.
>
> Alternatively, if you are fuzzing the hypercalls, which it sounds like
> you are, then you need to ensure that you blacklist operations such as
> SCHEDOP_shutdown and SCHEDOP_poll to avoid the fuzzer hitting legitimate
> hypercalls which shut down or block for indefinite periods of time.
>
> ~Andrew
>
-- 
Atenciosamente,
Charles F.'. Gonçalves

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Re: domain_crash_sync vs "plain crash"

[Wei Liu]

On Fri, May 11, 2018 at 07:43:58PM -0300, Charles Gonçalves wrote:
> "That is, without (physical
> or virtual, depending on component) serial console you're often unlikely to
> actually observe any messages connected to the crash."
> 
> I do not have any experience with serial console interaction on linux.
> Can you list some examples for both cases (virtual| physical), I'll glad to
> fully report any suspicious problem.
> 
> Thanks!
> 

See

https://wiki.xenproject.org/wiki/Xen_Serial_Console

Wei.

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