Re: [PATCH 0/2] Expose kallsyms data in vmcoreinfo note

Stephen Brennan
2022-05-23T18:27:49Z

Baoquan He <bhe@redhat.com> writes:
> On 05/16/22 at 05:05pm, Stephen Brennan wrote:
>> The kernel can be configured to contain a lot of introspection or
>> debugging information built-in, such as ORC for unwinding stack traces,
>> BTF for type information, and of course kallsyms. Debuggers could use
>> this information to navigate a core dump or live system, but they need
>> to be able to find it.
>>
>> This patch series adds the necessary symbols into vmcoreinfo, which
>> would allow a debugger to find and interpret the kallsyms table. Using
>> the kallsyms data, the debugger can then lookup any symbol, allowing it
>> to find ORC, BTF, or any other useful data.
>>
>> This would allow a live kernel, or core dump, to be debugged without
>> any DWARF debuginfo. This is useful for many cases: the debuginfo may
>> not have been generated, or you may not want to deploy the large files
>> everywhere you need them.
>>
>> I've demonstrated a proof of concept for this at LSF/MM+BPF during a
>> lighting talk. Using a work-in-progress branch of the drgn debugger, and
>> an extended set of BTF generated by a patched version of dwarves, I've
>> been able to open a core dump without any DWARF info and do basic tasks
>> such as enumerating slab caches, block devices, tasks, and doing
>> backtraces. I hope this series can be a first step toward a new
>> possibility of "DWARFless debugging".
>
> Thanks. Seems no reason to reject, even though I haven't tried drgn.
> And hope it has no security issue, e.g info leakage, at least I don't
> see it has. So,
>
> Acked-by: Baoquan He <bhe@redhat.com>

Thanks Baoquan! I don't believe we have any worries regarding security,
since the kallsyms data itself is already available to root via
/proc/kallsyms, and core dumps should already be treated as highly
sensitive data by anybody handling them.

Do you know which tree this patch will go through?

Thanks,
Stephen