Re: [PATCH 1/4] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE
From: Jisheng Zhang
Date: Mon Aug 19 2019 - 22:06:38 EST
On Tue, 20 Aug 2019 09:01:30 +0900 Masami Hiramatsu wrote:
> Hi Jisheng,
> On Mon, 19 Aug 2019 11:36:09 +0000
> Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> wrote:
> > For KPROBES_ON_FTRACE case, we need to adjust the kprobe's addr
> > correspondingly.
> No, I think you have misunderstood what the ftrace_call_adjust() does.
> Ftrace's rec->ip is already adjusted when initializing it. Kprobes
> checks the list after initialized (adjusted). So you don't need to
> adjust it again.
This is not to adjust the ftarce's rec->ip, but to adjust the struct kprobe
addr member. Because check_kprobe_address_safe()=>arch_check_ftrace_location
will check the kprobe's addr with ftrace's rec->ip. Since ftrace's rec->ip
is already adjusted, there will be mismatch if we don't adjust kprobe's addr
However, this patch is wrong. I should not update the kprobe's addr
for non-ftrace-entry. Will fix this in next version.
> BTW, this type of hidden adjustment should be avoided by design.
> If you find user specifies wrong address, return error instead of
> adjust it silently.
> Thank you,
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx>
> > ---
> > kernel/kprobes.c | 3 +++
> > 1 file changed, 3 insertions(+)
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 9873fc627d61..f8400753a8a9 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1560,6 +1560,9 @@ int register_kprobe(struct kprobe *p)
> > addr = kprobe_addr(p);
> > if (IS_ERR(addr))
> > return PTR_ERR(addr);
> > +#ifdef CONFIG_KPROBES_ON_FTRACE
> > + addr = (kprobe_opcode_t *)ftrace_call_adjust((unsigned long)addr);
> > +#endif
> > p->addr = addr;
> > ret = check_kprobe_rereg(p);
> > --
> > 2.23.0.rc1
> Masami Hiramatsu <mhiramat@xxxxxxxxxx>