linux-kernel - Re: [git pull] kgdb-light -v10

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 12 Feb 2008 14:34:51 -0500
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Roland McGrath <roland@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [git pull] kgdb-light -v10

Hi -

On Tue, Feb 12, 2008 at 10:20:10AM -0800, Andrew Morton wrote:
> [...]  Bear in mind that one of the things you do with kgdb is to
> modify kernel memory [...]

Just for completeness, keep in mind that one can already 
do these sorts of things on a batch basis using systemtap:


> int foo;
> 	...
> 	if (foo == 1)
> 		special_stuff();
> 	...
> 
> to trigger a particular behaviour at a particular time.  [...]

If "foo" is a global within a particular compliation unit, any old
function in that CU can be probed to set/get the global.  (Setting
incoming function parameters works too.)

# cat delayed-set.stp
   # set a systemtap script variable based on a /proc control file
   probe procfs("activate").write { setit = $value }
   global setit
   # check the systemtap global in order to set the kernel global
   probe kernel.function("foo_checking_fn") { 
      if (setit=="1") { setit = ""; $foo = 1 }
   }
# stap -g -m ds delayed-set.stp &
# echo 1 > /proc/systemtap/ds/activate


> OT: another thing you can do with kgdb is error-path testing:
> 	foo = kmalloc(...)
> BP->	if (!foo)
> 		recover();
> put a breakpoint on the !foo test and set foo to zero by hand.

# cat setit2.stp
  probe kernel.statement("*@.../function.c:222") { /*if (desired)*/ $foo = 0 }
# stap -g setit2.stp &


- FChE
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/