Messages in this thread | | | Date | Mon, 6 Jul 2015 16:18:15 +0530 | From | Pratyush Anand <> | Subject | Re: [PATCH 1/2] arm64: Blacklist non-kprobe-able symbols |
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On 06/07/2015:10:03:24 AM, Will Deacon wrote: > On Mon, Jul 06, 2015 at 06:03:21AM +0100, Pratyush Anand wrote: > > Add all function symbols which are called from do_debug_exception under > > NOKPROBE_SYMBOL, as they can not kprobed. > > It's a shame this has to be so manual, but I suppose it's done on a > best-effort basis to catch broken probe placement. > > If we miss a function and somebody probes it, do we just get stuck in a > recursive exception, or could we print something suggesting that a symbol > be annotated as NOKPROBE?
In some cases we land into a recursive reenter_kprobe:
echo "p kfree" > /sys/kernel/debug/tracing/kprobe_events echo "p single_step_handler" >> /sys/kernel/debug/tracing/kprobe_events echo 1 > /sys/kernel/debug/tracing/events/enable
[ 116.904194] BUG: failure at .../arch/arm64/kernel/kprobes.c:288/reenter_kprobe()!
In some other echo "p kfree" > /sys/kernel/debug/tracing/kprobe_events echo "p el0_sync" >> /sys/kernel/debug/tracing/kprobe_events echo 1 > /sys/kernel/debug/tracing/events/enable
Infinite loop of: [ 142.731336] Unexpected kernel single-step exception at EL1
In 1st case currently only address is printed. pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr); So, while in 1st case we may also print name of symbol, we can not do much in second case.
Now, I am running some test with all the symbols in /proc/kallsyms and I noticed that there might be few more symbols which may not allow kprobing. So, may be I will resend this series with updates.
~Pratyush
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