Messages in this thread | | | Date | Mon, 17 Mar 2008 12:59:05 +0200 | From | "Yakov Lerner" <> | Subject | Re: [PATCH] Subject: kprobes-x86: correct post-eip value in post_hander() |
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On Mon, Mar 17, 2008 at 7:19 AM, Ananth N Mavinakayanahalli <ananth@in.ibm.com> wrote: > On Sun, Mar 16, 2008 at 03:21:21AM -0500, Yakov Lerner wrote: > > > > I was trying to get the address of instruction to be executed > > next after the kprobed instruction. But regs->eip in post_handler() > > contains value which is useless to the user. It's pre-corrected value. > > This value is difficult to use without access to resume_execution(), which > > is not exported anyway. > > I moved the invocation of post_handler() to *after* resume_execution(). > > Now regs->eip contains meaningful value in post_handler(). > > > > I do not think this change breaks any backward-compatibility. > > To make meaning of the old value, post_handler() would need access to > > resume_execution() which is not exported. I have difficulty to believe > > that previous, uncorrected, regs->eip can be meaningfully used in > > post_handler(). > > resume_execution() exists not just for the program counter fixups after > out-of-line singlestepping, but is also as an insurance to put the > program counter back to the correct address in case the user's > post_handler() mucks around with it. That isn't possible with this > change :-(
I see your point. This can be prevented by saving and restoring regs->ip around the post_handler() call, no ? Current code is beautiful. Saving and restoring regs->ip would make this place look ugly.
Otoh, if the post_handler() wants to crash the kernel, it can do it in thousand ways, not just by trashing regs->ip, no ?
Yakov
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