On Thu, Jul 28, 2022 at 08:56:27PM +0800, Xu Kuohai wrote:
> On 7/28/2022 8:27 PM, Jiri Olsa wrote:
> > On Thu, Jul 28, 2022 at 07:40:48AM -0400, Xu Kuohai wrote:
> > > From: Xu Kuohai <xukuohai@xxxxxxxxxx>
> >
> > SNIP
> >
> > >
> > > It's caused by a NULL tr->fops passed to ftrace_set_filter_ip(). tr->fops
> > > is initialized to NULL and is assigned to an allocated memory address if
> > > CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS is enabled. Since there is no
> > > direct call on arm64 yet, the config can't be enabled.
> > >
> > > To fix it, call ftrace_set_filter_ip() only if tr->fops is not NULL.
> > >
> > > Fixes: 00963a2e75a8 ("bpf: Support bpf_trampoline on functions with IPMODIFY (e.g. livepatch)")
> > > Reported-by: Bruno Goncalves <bgoncalv@xxxxxxxxxx>
> > > Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
> > > Tested-by: Bruno Goncalves <bgoncalv@xxxxxxxxxx>
> > > Acked-by: Song Liu <songliubraving@xxxxxx>
> > > ---
> > > kernel/bpf/trampoline.c | 11 +++++++++--
> > > 1 file changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> > > index 42e387a12694..0d5a9e0b9a7b 100644
> > > --- a/kernel/bpf/trampoline.c
> > > +++ b/kernel/bpf/trampoline.c
> > > @@ -255,8 +255,15 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
> > > return -ENOENT;
> > > if (tr->func.ftrace_managed) {
> > > - ftrace_set_filter_ip(tr->fops, (unsigned long)ip, 0, 0);
> > > - ret = register_ftrace_direct_multi(tr->fops, (long)new_addr);
> > > + if (tr->fops)
> > > + ret = ftrace_set_filter_ip(tr->fops, (unsigned long)ip,
> > > + 0, 0);
> > > + else
> > > + ret = -ENOTSUPP;
> > > +
> > > + if (!ret)
> > > + ret = register_ftrace_direct_multi(tr->fops,
> > > + (long)new_addr);
> > > } else {
> > > ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
> > > }
> >
> > do we need to do the same also in unregister_fentry and modify_fentry ?
> >
>
> No need for now, this is the only place where we call ftrace_set_filter_ip().
>
> tr->fops is passed to ftrace_set_filter_ip() and *ftrace_direct_multi()
> functions, and when CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS is not enabled,
> the *ftrace_direct_multi()s do nothing except returning an error code, so
> it's safe to pass NULL to them.
ok, makes sense
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
jirka
