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From:   Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To:     Masami Hiramatsu <mhiramat@kernel.org>
CC:     Catalin Marinas <catalin.marinas@arm.com>,
        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>,
        "David S. Miller" <davem@davemloft.net>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
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        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/4] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE
Thread-Topic: [PATCH 1/4] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE
Thread-Index: AQHVVoJFk8X59Zi3AUirAcI9pTWKbqcDJ9IAgAAfqgA=
Date:   Tue, 20 Aug 2019 02:05:58 +0000
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References: <20190819192422.5ed79702@xhacker.debian>
        <20190819192505.483c0bf0@xhacker.debian>
        <20190820090130.844fc064030db67efb05ceb1@kernel.org>
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On Tue, 20 Aug 2019 09:01:30 +0900 Masami Hiramatsu wrote:

>=20
> Hi Jisheng,

Hi,

>=20
> On Mon, 19 Aug 2019 11:36:09 +0000
> Jisheng Zhang <Jisheng.Zhang@synaptics.com> wrote:
>=20
> > For KPROBES_ON_FTRACE case, we need to adjust the kprobe's addr
> > correspondingly. =20
>=20
> 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()=3D>arch_check_ftrace_locat=
ion
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 add=
r
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

>=20
> 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.
>=20
> Thank you,
>=20
> >
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.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 =3D kprobe_addr(p);
> >       if (IS_ERR(addr))
> >               return PTR_ERR(addr);
> > +#ifdef CONFIG_KPROBES_ON_FTRACE
> > +     addr =3D (kprobe_opcode_t *)ftrace_call_adjust((unsigned long)add=
r);
> > +#endif
> >       p->addr =3D addr;
> >
> >       ret =3D check_kprobe_rereg(p);
> > --
> > 2.23.0.rc1
> > =20
>=20
>=20
> --
> Masami Hiramatsu <mhiramat@kernel.org>