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SubjectRe: [PATCH] jprobes: Ensure that the probepoint is at function entry
On Wed, 5 Jul 2017 12:42:16 +0200
Ingo Molnar <mingo@kernel.org> wrote:

>
> * Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> wrote:
>
> > Similar to commit 90ec5e89e393c ("kretprobes: Ensure probe location is
> > at function entry"), ensure that the jprobe probepoint is at function
> > entry.

Sorry I missed it.

> >
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> > ---
> > kernel/kprobes.c | 9 +++++++--
> > 1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index adfe3b4cfe05..950018609339 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1776,9 +1776,14 @@ int register_jprobes(struct jprobe **jps, int num)
> > jp = jps[i];
> > addr = arch_deref_entry_point(jp->entry);
> >
> > - /* Verify probepoint is a function entry point */
> > + /*
> > + * Verify probepoint as well as the jprobe handler are
> > + * function entry points.
> > + */
> > if (kallsyms_lookup_size_offset(addr, NULL, &offset) &&
> > - offset == 0) {
> > + offset == 0 &&
> > + function_offset_within_entry(jp->kp.addr,
> > + jp->kp.symbol_name, jp->kp.offset)) {

Here, you are agressively use tab, please align the indent to
same level of kallsyms_lookup_size_offset?

> > jp->kp.pre_handler = setjmp_pre_handler;
> > jp->kp.break_handler = longjmp_break_handler;
> > ret = register_kprobe(&jp->kp);
>
> Yeah, so I agree with the fix, but the line breaks there are disgusting.
>
> One solution would be to split out the iterator into a register_jprobe() function.
> Also, introduce a 'kp' temporary variable to simplify and shorten usage.
>

Agreed.

> Also, 'function_offset_within_entry' is way too long a name, and it's also a
> minomer I think. The purpose of this function is to enforce that the relative
> 'offset' of a new probe is at the standard function entry offset: i.e. 0 on most
> architectures, and some ABI dependent constant on PowerPC, right?
>
> That's not at all clear from that name, plus it's a global namespace symbol, yet
> has no 'kprobes' prefix. So it should be named something like
> 'kprobe_offset_valid()' or such, with an arch_kprobe_offset_valid() counterpart.

Hmm, I would rather like kprobe_within_entry(), since offset != 0 is
actually valid for normal kprobe, that is kretprobe and jprobe limitation.

Thank you,

>
> All of these cleanups should be in separate patches - with the fix in the end.
>
> Thanks,
>
> Ingo


--
Masami Hiramatsu <mhiramat@kernel.org>

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