linux-kernel - Re: [PATCH 1/4] kprobes: adjust kprobe addr for KPROBES_ON

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Message-ID: <20190820095450.3eb3120b@xhacker.debian>
Date:   Tue, 20 Aug 2019 02:05:58 +0000
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "David S. Miller" <davem@...emloft.net>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE

On Tue, 20 Aug 2019 09:01:30 +0900 Masami Hiramatsu wrote:

> 
> Hi Jisheng,

Hi,

> 
> On Mon, 19 Aug 2019 11:36:09 +0000
> Jisheng Zhang <Jisheng.Zhang@...aptics.com> 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
correspondingly.

However, this patch is wrong. I should not update the kprobe's addr
for non-ftrace-entry. Will fix this in next version.

Thanks

> 
> 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@...aptics.com>
> > ---
> >  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@...nel.org>