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

From: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Jonathan Corbet <corbet@lwn.net>, Will Deacon <will@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 2/3] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE
Date: Wed, 21 Aug 2019 02:50:12 +0000	[thread overview]
Message-ID: <20190821103857.14d2a40d@xhacker.debian> (raw)
In-Reply-To: <20190821110739.fb3ab6b69423dff64a3b4a29@kernel.org>

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 <Jisheng.Zhang@synaptics.com> 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 <Jisheng.Zhang@synaptics.com>
> > ---
> >  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 <mhiramat@kernel.org>