Re: Re: new module to check constant memory for corruption

[Richard Weinberger]

On Sun, Apr 13, 2014 at 12:14 PM,  <Alexander.Kleinsorge@xxxxxx> wrote:
> Hi Andi,
>
> the module considers only the adress range between: kallsyms_lookup_name("_text") .. kallsyms_lookup_name("__end_rodata").
> this range has a typical size of 10..20 mb (depending on kernel-version and arch).
> see files: linux-3.*\arch\x86\mm\init_32.c + init_64.c
> function: void mark_rodata_ro(void)
> "Write protecting the kernel text: %luk\n"
> "Write protecting the kernel read-only data: %luk\n"
> dmesg | grep protecting
>
> your question: there are no writes in this write protected adress range (e.g. kernel code).

And what happens if one enables dynamic ftrace or other kernel
features which modify kernel code?

> my idea is to calculate a checksum (xor is fastest) over this range and check later (periodically) if its unchanged.
> see source code download (5 KB): http://tauruz.homeip.net/ramcheck.tgz
> the code is working fine and the checksum is (as expected) constant (at least for many hours).
>
> regards, Alexander
>
>
> Gesendet: Sonntag, 13. April 2014 um 05:00 Uhr
> Von: "Andi Kleen" <andi@xxxxxxxxxxxxxx>
> An: Alexander.Kleinsorge@xxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Betreff: Re: new module to check constant memory for corruption
> Alexander.Kleinsorge@xxxxxx writes:
>
>> ramcheck kernel module
>> new module to check constant memory for corruption
>>
>> detect corruption of constant kernel memory (text and data) periodically.
>> runtime costs about 1..2 ms per sec (about 10 mb with 5 mb/ms),
>> which is distributed over 8 (BLOCKS) time partitions (less than half
>> ms per sec).
>> in case of checksum (xor) error, an kernel log is posted.
>> manual trigger via /proc/ramcheck is possible.
>> range: kallsyms_lookup_name("_text") .. kallsyms_lookup_name("__end_rodata")
>
>
> Can you explain how this works? How does it handle legal writes?
>
> If it just checks its own memory it could be done in user space.
>
> -Andi
>
> --
> ak@xxxxxxxxxxxxxxx -- Speaking for myself only
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-- 
Thanks,
//richard
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