diff mbox series

[PATCHv4,bpf-next,7/8] libbpf: Allow specification of "kprobe/function+offset"

Message ID 20210714094400.396467-8-jolsa@kernel.org
State New
Headers show
Series bpf, x86: Add bpf_get_func_ip helper | expand

Commit Message

Jiri Olsa July 14, 2021, 9:43 a.m. UTC 
From: Alan Maguire <alan.maguire@oracle.com>

kprobes can be placed on most instructions in a function, not
just entry, and ftrace and bpftrace support the function+offset
notification for probe placement.  Adding parsing of func_name
into func+offset to bpf_program__attach_kprobe() allows the
user to specify

SEC("kprobe/bpf_fentry_test5+0x6")

...for example, and the offset can be passed to perf_event_open_probe()
to support kprobe attachment.

[jolsa: changed original code to use bpf_program__attach_kprobe_opts
and use dynamic allocation in sscanf]

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/lib/bpf/libbpf.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

Comments

Andrii Nakryiko July 17, 2021, 1:42 a.m. UTC | #1 
On Wed, Jul 14, 2021 at 2:45 AM Jiri Olsa <jolsa@redhat.com> wrote:
>

> From: Alan Maguire <alan.maguire@oracle.com>

>

> kprobes can be placed on most instructions in a function, not

> just entry, and ftrace and bpftrace support the function+offset

> notification for probe placement.  Adding parsing of func_name

> into func+offset to bpf_program__attach_kprobe() allows the

> user to specify

>

> SEC("kprobe/bpf_fentry_test5+0x6")

>

> ...for example, and the offset can be passed to perf_event_open_probe()

> to support kprobe attachment.

>

> [jolsa: changed original code to use bpf_program__attach_kprobe_opts

> and use dynamic allocation in sscanf]

>

> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

> ---

>  tools/lib/bpf/libbpf.c | 24 ++++++++++++++++++++++--

>  1 file changed, 22 insertions(+), 2 deletions(-)

>

> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c

> index d93a6f9408d1..abe6d4842bb0 100644

> --- a/tools/lib/bpf/libbpf.c

> +++ b/tools/lib/bpf/libbpf.c

> @@ -10348,6 +10348,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,

>

>  struct bpf_program_attach_kprobe_opts {

>         bool retprobe;

> +       unsigned long offset;

>  };

>

>  static struct bpf_link*

> @@ -10360,7 +10361,7 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,

>         int pfd, err;

>

>         pfd = perf_event_open_probe(false /* uprobe */, opts->retprobe, func_name,

> -                                   0 /* offset */, -1 /* pid */);

> +                                   opts->offset, -1 /* pid */);

>         if (pfd < 0) {

>                 pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",

>                         prog->name, opts->retprobe ? "kretprobe" : "kprobe", func_name,

> @@ -10394,12 +10395,31 @@ static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,

>                                       struct bpf_program *prog)

>  {

>         struct bpf_program_attach_kprobe_opts opts;

> +       unsigned long offset = 0;

> +       struct bpf_link *link;

>         const char *func_name;

> +       char *func;

> +       int n, err;

>

>         func_name = prog->sec_name + sec->len;

>         opts.retprobe = strcmp(sec->sec, "kretprobe/") == 0;

>

> -       return bpf_program__attach_kprobe_opts(prog, func_name, &opts);

> +       n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%lx", &func, &offset);


could have used %li here to support both +0xabc and +123 forms

> +       if (n < 1) {

> +               err = -EINVAL;

> +               pr_warn("kprobe name is invalid: %s\n", func_name);

> +               return libbpf_err_ptr(err);

> +       }

> +       if (opts.retprobe && offset != 0) {

> +               err = -EINVAL;


leaking func here


> +               pr_warn("kretprobes do not support offset specification\n");

> +               return libbpf_err_ptr(err);

> +       }

> +

> +       opts.offset = offset;

> +       link = bpf_program__attach_kprobe_opts(prog, func, &opts);

> +       free(func);

> +       return link;

>  }

>

>  struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,

> --

> 2.31.1

>
Jiri Olsa July 18, 2021, 7:32 p.m. UTC | #2 
On Fri, Jul 16, 2021 at 06:42:05PM -0700, Andrii Nakryiko wrote:
> On Wed, Jul 14, 2021 at 2:45 AM Jiri Olsa <jolsa@redhat.com> wrote:

> >

> > From: Alan Maguire <alan.maguire@oracle.com>

> >

> > kprobes can be placed on most instructions in a function, not

> > just entry, and ftrace and bpftrace support the function+offset

> > notification for probe placement.  Adding parsing of func_name

> > into func+offset to bpf_program__attach_kprobe() allows the

> > user to specify

> >

> > SEC("kprobe/bpf_fentry_test5+0x6")

> >

> > ...for example, and the offset can be passed to perf_event_open_probe()

> > to support kprobe attachment.

> >

> > [jolsa: changed original code to use bpf_program__attach_kprobe_opts

> > and use dynamic allocation in sscanf]

> >

> > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>

> > ---

> >  tools/lib/bpf/libbpf.c | 24 ++++++++++++++++++++++--

> >  1 file changed, 22 insertions(+), 2 deletions(-)

> >

> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c

> > index d93a6f9408d1..abe6d4842bb0 100644

> > --- a/tools/lib/bpf/libbpf.c

> > +++ b/tools/lib/bpf/libbpf.c

> > @@ -10348,6 +10348,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,

> >

> >  struct bpf_program_attach_kprobe_opts {

> >         bool retprobe;

> > +       unsigned long offset;

> >  };

> >

> >  static struct bpf_link*

> > @@ -10360,7 +10361,7 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,

> >         int pfd, err;

> >

> >         pfd = perf_event_open_probe(false /* uprobe */, opts->retprobe, func_name,

> > -                                   0 /* offset */, -1 /* pid */);

> > +                                   opts->offset, -1 /* pid */);

> >         if (pfd < 0) {

> >                 pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",

> >                         prog->name, opts->retprobe ? "kretprobe" : "kprobe", func_name,

> > @@ -10394,12 +10395,31 @@ static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,

> >                                       struct bpf_program *prog)

> >  {

> >         struct bpf_program_attach_kprobe_opts opts;

> > +       unsigned long offset = 0;

> > +       struct bpf_link *link;

> >         const char *func_name;

> > +       char *func;

> > +       int n, err;

> >

> >         func_name = prog->sec_name + sec->len;

> >         opts.retprobe = strcmp(sec->sec, "kretprobe/") == 0;

> >

> > -       return bpf_program__attach_kprobe_opts(prog, func_name, &opts);

> > +       n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%lx", &func, &offset);

> 

> could have used %li here to support both +0xabc and +123 forms


ok

> 

> > +       if (n < 1) {

> > +               err = -EINVAL;

> > +               pr_warn("kprobe name is invalid: %s\n", func_name);

> > +               return libbpf_err_ptr(err);

> > +       }

> > +       if (opts.retprobe && offset != 0) {

> > +               err = -EINVAL;

> 

> leaking func here


ugh.. thanks

jirka

> 

> 

> > +               pr_warn("kretprobes do not support offset specification\n");

> > +               return libbpf_err_ptr(err);

> > +       }

> > +

> > +       opts.offset = offset;

> > +       link = bpf_program__attach_kprobe_opts(prog, func, &opts);

> > +       free(func);

> > +       return link;

> >  }

> >

> >  struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,

> > --

> > 2.31.1

> >

>
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d93a6f9408d1..abe6d4842bb0 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10348,6 +10348,7 @@  static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
 
 struct bpf_program_attach_kprobe_opts {
 	bool retprobe;
+	unsigned long offset;
 };
 
 static struct bpf_link*
@@ -10360,7 +10361,7 @@  bpf_program__attach_kprobe_opts(struct bpf_program *prog,
 	int pfd, err;
 
 	pfd = perf_event_open_probe(false /* uprobe */, opts->retprobe, func_name,
-				    0 /* offset */, -1 /* pid */);
+				    opts->offset, -1 /* pid */);
 	if (pfd < 0) {
 		pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",
 			prog->name, opts->retprobe ? "kretprobe" : "kprobe", func_name,
@@ -10394,12 +10395,31 @@  static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,
 				      struct bpf_program *prog)
 {
 	struct bpf_program_attach_kprobe_opts opts;
+	unsigned long offset = 0;
+	struct bpf_link *link;
 	const char *func_name;
+	char *func;
+	int n, err;
 
 	func_name = prog->sec_name + sec->len;
 	opts.retprobe = strcmp(sec->sec, "kretprobe/") == 0;
 
-	return bpf_program__attach_kprobe_opts(prog, func_name, &opts);
+	n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%lx", &func, &offset);
+	if (n < 1) {
+		err = -EINVAL;
+		pr_warn("kprobe name is invalid: %s\n", func_name);
+		return libbpf_err_ptr(err);
+	}
+	if (opts.retprobe && offset != 0) {
+		err = -EINVAL;
+		pr_warn("kretprobes do not support offset specification\n");
+		return libbpf_err_ptr(err);
+	}
+
+	opts.offset = offset;
+	link = bpf_program__attach_kprobe_opts(prog, func, &opts);
+	free(func);
+	return link;
 }
 
 struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,