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Thu, 02 Jun 2022 16:01:18 -0700 (PDT) MIME-Version: 1.0 References: <20220527205611.655282-1-jolsa@kernel.org> <20220527205611.655282-4-jolsa@kernel.org> In-Reply-To: <20220527205611.655282-4-jolsa@kernel.org> From: Andrii Nakryiko Date: Thu, 2 Jun 2022 16:01:07 -0700 Message-ID: Subject: Re: [PATCH bpf-next 3/3] bpf: Force cookies array to follow symbols sorting To: Jiri Olsa Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Networking , bpf , lkml , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Steven Rostedt , Masami Hiramatsu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 27, 2022 at 1:57 PM Jiri Olsa 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 > --- > 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); > + if (!cookies) { > + err = -ENOMEM; > + goto error; > + } > + if (copy_from_user(cookies, ucookies, size)) { > + err = -EFAULT; > + goto error; > + } > + } > + > if (uaddrs) { > if (copy_from_user(addrs, uaddrs, size)) { > err = -EFAULT; > @@ -2480,26 +2517,24 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr > if (err) > goto error; > > - sort(us.syms, cnt, sizeof(*us.syms), symbols_cmp, NULL); > + if (cookies) { > + struct multi_symbols_sort data = { > + .cookies = cookies, > + .funcs = us.syms, > + }; > + > + sort_r(us.syms, cnt, sizeof(*us.syms), symbols_cmp_r, > + symbols_swap_r, &data); > + } else { > + sort(us.syms, cnt, sizeof(*us.syms), symbols_cmp, NULL); > + } maybe just always do sort_r, swap callback can just check if cookie array is NULL and if not, additionally swap cookies? why have all these different callbacks and complicate the code unnecessarily? > + > err = ftrace_lookup_symbols(us.syms, cnt, addrs); > free_user_syms(&us); > if (err) > goto error; > } > > - ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies); > - if (ucookies) { > - cookies = kvmalloc(size, GFP_KERNEL); > - if (!cookies) { > - err = -ENOMEM; > - goto error; > - } > - if (copy_from_user(cookies, ucookies, size)) { > - err = -EFAULT; > - goto error; > - } > - } > - > link = kzalloc(sizeof(*link), GFP_KERNEL); > if (!link) { > err = -ENOMEM; > -- > 2.35.3 >