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

[Alexander . Kleinsorge]

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).Â
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).
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:ÂSonntag, 13. April 2014 um 05:00 Uhr
Von:Â"Andi Kleen" <andi@xxxxxxxxxxxxxx>
An:ÂAlexander.Kleinsorge@xxxxxx
Cc:Âlinux-kernel@xxxxxxxxxxxxxxx
Betreff:ÂRe: 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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