linux-kernel - Re: [PATCH bpf-next 3/3] bpf: Force cookies array to follow symbols sorting

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Date:   Fri, 3 Jun 2022 12:23:11 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH bpf-next 3/3] bpf: Force cookies array to follow symbols
 sorting

On Thu, Jun 02, 2022 at 04:02:28PM -0700, Andrii Nakryiko wrote:
> On Thu, Jun 2, 2022 at 4:01 PM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
> >
> > On Fri, May 27, 2022 at 1:57 PM Jiri Olsa <jolsa@...nel.org> wrote:
> > >
> > > When user specifies symbols and cookies for kprobe_multi link
> > > interface it's very likely the cookies will be misplaced and
> > > returned to wrong functions (via get_attach_cookie helper).
> > >
> > > The reason is that to resolve the provided functions we sort
> > > them before passing them to ftrace_lookup_symbols, but we do
> > > not do the same sort on the cookie values.
> > >
> > > Fixing this by using sort_r function with custom swap callback
> > > that swaps cookie values as well.
> > >
> > > Fixes: 0236fec57a15 ("bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link")
> > > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > > ---
> > >  kernel/trace/bpf_trace.c | 65 ++++++++++++++++++++++++++++++----------
> > >  1 file changed, 50 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > > index 10b157a6d73e..e5c423b835ab 100644
> > > --- a/kernel/trace/bpf_trace.c
> > > +++ b/kernel/trace/bpf_trace.c
> > > @@ -2423,7 +2423,12 @@ kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip,
> > >         kprobe_multi_link_prog_run(link, entry_ip, regs);
> > >  }
> > >
> > > -static int symbols_cmp(const void *a, const void *b)
> > > +struct multi_symbols_sort {
> > > +       const char **funcs;
> > > +       u64 *cookies;
> > > +};
> > > +
> > > +static int symbols_cmp_r(const void *a, const void *b, const void *priv)
> > >  {
> > >         const char **str_a = (const char **) a;
> > >         const char **str_b = (const char **) b;
> > > @@ -2431,6 +2436,25 @@ static int symbols_cmp(const void *a, const void *b)
> > >         return strcmp(*str_a, *str_b);
> > >  }
> > >
> > > +static void symbols_swap_r(void *a, void *b, int size, const void *priv)
> > > +{
> > > +       const struct multi_symbols_sort *data = priv;
> > > +       const char **name_a = a, **name_b = b;
> > > +       u64 *cookie_a, *cookie_b;
> > > +
> > > +       cookie_a = data->cookies + (name_a - data->funcs);
> > > +       cookie_b = data->cookies + (name_b - data->funcs);
> > > +
> > > +       /* swap name_a/name_b and cookie_a/cookie_b values */
> > > +       swap(*name_a, *name_b);
> > > +       swap(*cookie_a, *cookie_b);
> > > +}
> > > +
> > > +static int symbols_cmp(const void *a, const void *b)
> > > +{
> > > +       return symbols_cmp_r(a, b, NULL);
> > > +}
> > > +
> > >  int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> > >  {
> > >         struct bpf_kprobe_multi_link *link = NULL;
> > > @@ -2468,6 +2492,19 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> > >         if (!addrs)
> > >                 return -ENOMEM;
> > >
> > > +       ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
> > > +       if (ucookies) {
> > > +               cookies = kvmalloc(size, GFP_KERNEL);
> 
> oh, and you'll have to rebase anyways after kvmalloc_array patch

true, that kvmalloc_array change went to bpf-next/master,
but as Song mentioned this patchset should probably go for bpf/master?

I'm fine either way, let me know ;-)

thanks,
jirka