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

Message ID 20210714094400.396467-8-jolsa@kernel.org (mailing list archive)
State Accepted
Delegated to: BPF
Headers show
Series bpf, x86: Add bpf_get_func_ip helper | expand

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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,