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).
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" <a...@firstfloor.org>
An: alexander.kleinso...@gmx.de
Cc: linux-kernel@vger.kernel.org
Betreff: Re: new module to check constant memory for corruption
alexander.kleinso...@gmx.de 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
--
a...@linux.intel.com -- Speaking for myself only
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