Subject: Re: [PATCH v2 2/3] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE

From: Jisheng Zhang <[email-masked]>
Date: Wed, 21 Aug 2019 02:50:12 +0000

Hi,

On Wed, 21 Aug 2019 11:07:39 +0900 Masami Hiramatsu wrote:

> 
> 
> Hi Jisheng,
> 
> On Tue, 20 Aug 2019 03:53:31 +0000
> Jisheng Zhang <[email-masked]> wrote:
> 
> > For KPROBES_ON_FTRACE case, we need to adjust the kprobe's addr
> > correspondingly.  
> 
> Either KPROBES_ON_FTRACE=y or not, ftrace_location() check must be
> done correctly. If it failed, kprobes can modify the instruction
> which can be modified by ftrace.
> 
> >
> > Signed-off-by: Jisheng Zhang <[email-masked]>
> > ---
> >  kernel/kprobes.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 9873fc627d61..3fd2f68644da 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1484,15 +1484,19 @@ static inline int check_kprobe_rereg(struct kprobe *p)
> >
> >  int __weak arch_check_ftrace_location(struct kprobe *p)
> >  {
> > -     unsigned long ftrace_addr;
> > +     unsigned long ftrace_addr, addr = (unsigned long)p->addr;
> >
> > -     ftrace_addr = ftrace_location((unsigned long)p->addr);
> > +#ifdef CONFIG_KPROBES_ON_FTRACE
> > +     addr = ftrace_call_adjust(addr);
> > +#endif
> > +     ftrace_addr = ftrace_location(addr);  
> 
> No, this is not right way to do. If we always need to adjust address
> before calling ftrace_location(), something wrong with ftrace_location()
> interface.
> ftrace_location(addr) must check the address is within the range which
> can be changed by ftrace. (dyn->ip <= addr <= dyn->ip+MCOUNT_INSN_SIZE)

yeah! I will try Naveen's suggestion, I.E patch kprobe_lookup_name() instead.

Thanks

> 
> 
> >       if (ftrace_addr) {
> >  #ifdef CONFIG_KPROBES_ON_FTRACE
> >               /* Given address is not on the instruction boundary */
> > -             if ((unsigned long)p->addr != ftrace_addr)
> > +             if (addr != ftrace_addr)
> >                       return -EILSEQ;
> >               p->flags |= KPROBE_FLAG_FTRACE;
> > +             p->addr = (kprobe_opcode_t *)addr;  
> 
> And again, please don't change the p->addr silently.
> 
> Thank you,
> 
> >  #else        /* !CONFIG_KPROBES_ON_FTRACE */
> >               return -EINVAL;
> >  #endif
> > --
> > 2.23.0.rc1
> >  
> 
> 
> --
> Masami Hiramatsu <[email-masked]>

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