On June 7, 2019 11:10:19 AM PDT, Andy Lutomirski <l...@amacapital.net> wrote: > > >> On Jun 7, 2019, at 10:34 AM, Peter Zijlstra <pet...@infradead.org> >wrote: >> >> On Sat, Jun 08, 2019 at 12:47:08AM +0900, Masami Hiramatsu wrote: >> >>>> This fits almost all text_poke_bp() users, except >>>> arch_unoptimize_kprobe() which restores random text, and for that >site >>>> we have to build an explicit emulate instruction. >>> >>> Hm, actually it doesn't restores randome text, since the first byte >>> must always be int3. As the function name means, it just unoptimizes >>> (jump based optprobe -> int3 based kprobe). >>> Anyway, that is not an issue. With this patch, optprobe must still >work. >> >> I thought it basically restored 5 bytes of original text (with no >> guarantee it is a single instruction, or even a complete >instruction), >> with the first byte replaced with INT3. >> > >I am surely missing some kprobe context, but is it really safe to use >this mechanism to replace more than one instruction?
I don't see how it could be, except *perhaps* inside an NMI have, because you could have a preempted or interrupted now having an in-memory IP pointing inside the middle of the region you are intending to patch. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
