Date: Sat, 15 Sep 2001 05:50:50 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Sansonetti Laurent <lorenzo@linuxbe.org> Cc: freebsd-hackers@freebsd.org Subject: Re: storing routine code in kernel memory using kvm interface Message-ID: <3BA34EAA.38878044@mindspring.com> References: <001501c13de3$45dd8320$0201a8c0@teledisnet.be>
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Sansonetti Laurent wrote: > > Hi, > > Is there a way to store a function in kernel memory using KVM interface ? > > I have written a tty spy'er, which simply hijack discipline line entries for > a tty, and as you know probably, those routines must be situated in kernel > land. > > I know that I should use KLD for that, but i'm still curious.. No. You can not allocate memory safely to prevent the kernel reusing it and stomping your code, and you can not guarantee your hook installation will be done atomically without getting context switched or interrupted via a hardware interrupt, thus panic'ing the kernel. Not to mention that you would have to know a huge amount about the VM system to establish mappings, and those mappings wouldn't be atomic, either, and without them, your kernel would panic with a "page not present". Use a KLD instead, unless this is a cracking tool, in which case go ahead and use /dev/kmem, if it's writeable, since repeated crashes with tracebacks pointing to a program using your uid and having /dev/kmem open will get your admin to you-proof his box. 8-). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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