diff mbox series

[bpf-next,v4,3/5] libbpf: Add BPF_PROG_BIND_MAP syscall and use it on .metadata section

Message ID 20200909182406.3147878-4-sdf@google.com
State New
Headers show
Series Allow storage of flexible metadata information for eBPF programs | expand

Commit Message

Stanislav Fomichev Sept. 9, 2020, 6:24 p.m. UTC 
From: YiFei Zhu <zhuyifei@google.com>

The patch adds a simple wrapper bpf_prog_bind_map around the syscall.
When the libbpf tries to load a program, it will probe the kernel for
the support of this syscall and unconditionally bind .rodata section
to the program.

Cc: YiFei Zhu <zhuyifei1999@gmail.com>
Signed-off-by: YiFei Zhu <zhuyifei@google.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 tools/lib/bpf/bpf.c      | 13 ++++++
 tools/lib/bpf/bpf.h      |  8 ++++
 tools/lib/bpf/libbpf.c   | 94 ++++++++++++++++++++++++++++++++--------
 tools/lib/bpf/libbpf.map |  1 +
 4 files changed, 98 insertions(+), 18 deletions(-)

Comments

Stanislav Fomichev Sept. 11, 2020, 3:49 p.m. UTC | #1 
On Thu, Sep 10, 2020 at 12:41 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Wed, Sep 9, 2020 at 11:25 AM Stanislav Fomichev <sdf@google.com> wrote:
> >
> > From: YiFei Zhu <zhuyifei@google.com>
> >
> > The patch adds a simple wrapper bpf_prog_bind_map around the syscall.
> > When the libbpf tries to load a program, it will probe the kernel for
> > the support of this syscall and unconditionally bind .rodata section
>
> btw, you subject is out of sync, still mentions .metadata
Ooops, will fix, thanks!

> > to the program.
> >
> > Cc: YiFei Zhu <zhuyifei1999@gmail.com>
> > Signed-off-by: YiFei Zhu <zhuyifei@google.com>
>
> Please drop zhuyifei@google.com from CC list (it's unreachable), when
> you submit a new version.
I think git-send-email automatically adds it because of the sign-off,
let me try to see if I can remove it. I guess I can just do
s/zhuyifei@google.com/zhuyifei1999@gmail.com/ to make
it quiet.

> > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> > ---
> >  tools/lib/bpf/bpf.c      | 13 ++++++
> >  tools/lib/bpf/bpf.h      |  8 ++++
> >  tools/lib/bpf/libbpf.c   | 94 ++++++++++++++++++++++++++++++++--------
> >  tools/lib/bpf/libbpf.map |  1 +
> >  4 files changed, 98 insertions(+), 18 deletions(-)
> >
> > diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> > index 82b983ff6569..5f6c5676cc45 100644
> > --- a/tools/lib/bpf/bpf.c
> > +++ b/tools/lib/bpf/bpf.c
> > @@ -872,3 +872,16 @@ int bpf_enable_stats(enum bpf_stats_type type)
> >
> >         return sys_bpf(BPF_ENABLE_STATS, &attr, sizeof(attr));
> >  }
> > +
> > +int bpf_prog_bind_map(int prog_fd, int map_fd,
> > +                     const struct bpf_prog_bind_opts *opts)
> > +{
> > +       union bpf_attr attr;
> > +
>
> you forgot OPTS_VALID check here
Good point, will do!

> > @@ -3748,26 +3749,40 @@ static int probe_kern_global_data(void)
> >         map_attr.value_size = 32;
> >         map_attr.max_entries = 1;
> >
> > -       map = bpf_create_map_xattr(&map_attr);
> > -       if (map < 0) {
> > -               ret = -errno;
> > -               cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
> > +       *map = bpf_create_map_xattr(&map_attr);
> > +       if (*map < 0) {
> > +               err = errno;
> > +               cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
> >                 pr_warn("Error in %s():%s(%d). Couldn't create simple array map.\n",
> > -                       __func__, cp, -ret);
> > -               return ret;
> > +                       __func__, cp, -err);
> > +               return;
> >         }
> >
> > -       insns[0].imm = map;
> > +       insns[0].imm = *map;
>
> I think I already complained about this? You are assuming that
> insns[0] is BPF_LD_MAP_VALUE, which is true only for one case out of
> two already! It's just by luck that probe_prog_bind_map works because
> the verifier ignores the exit code, apparently.
>
> If this doesn't generalize well, don't generalize. But let's not do a
> blind instruction rewrite, which will cause tons of confusion later.
I might have missed your previous comment, sorry about that.
Agreed, it might be easier to just copy-paste the original function
and explicitly change the insns.

> [...]
>
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 92ceb48a5ca2..0b7830f4ff8b 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -308,4 +308,5 @@ LIBBPF_0.2.0 {
> >                 perf_buffer__epoll_fd;
> >                 perf_buffer__consume_buffer;
> >                 xsk_socket__create_shared;
> > +               bpf_prog_bind_map;
>
> please keep this list sorted
Sure, will do!
diff mbox series

Patch

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 82b983ff6569..5f6c5676cc45 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -872,3 +872,16 @@  int bpf_enable_stats(enum bpf_stats_type type)
 
 	return sys_bpf(BPF_ENABLE_STATS, &attr, sizeof(attr));
 }
+
+int bpf_prog_bind_map(int prog_fd, int map_fd,
+		      const struct bpf_prog_bind_opts *opts)
+{
+	union bpf_attr attr;
+
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_bind_map.prog_fd = prog_fd;
+	attr.prog_bind_map.map_fd = map_fd;
+	attr.prog_bind_map.flags = OPTS_GET(opts, flags, 0);
+
+	return sys_bpf(BPF_PROG_BIND_MAP, &attr, sizeof(attr));
+}
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 015d13f25fcc..8c1ac4b42f90 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -243,6 +243,14 @@  LIBBPF_API int bpf_task_fd_query(int pid, int fd, __u32 flags, char *buf,
 enum bpf_stats_type; /* defined in up-to-date linux/bpf.h */
 LIBBPF_API int bpf_enable_stats(enum bpf_stats_type type);
 
+struct bpf_prog_bind_opts {
+	size_t sz; /* size of this struct for forward/backward compatibility */
+	__u32 flags;
+};
+#define bpf_prog_bind_opts__last_field flags
+
+LIBBPF_API int bpf_prog_bind_map(int prog_fd, int map_fd,
+				 const struct bpf_prog_bind_opts *opts);
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 550950eb1860..f500ae7e9126 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -174,6 +174,8 @@  enum kern_feature_id {
 	FEAT_EXP_ATTACH_TYPE,
 	/* bpf_probe_read_{kernel,user}[_str] helpers */
 	FEAT_PROBE_READ_KERN,
+	/* BPF_PROG_BIND_MAP is supported */
+	FEAT_PROG_BIND_MAP,
 	__FEAT_CNT,
 };
 
@@ -409,6 +411,7 @@  struct bpf_object {
 	struct extern_desc *externs;
 	int nr_extern;
 	int kconfig_map_idx;
+	int rodata_map_idx;
 
 	bool loaded;
 	bool has_subcalls;
@@ -1070,6 +1073,7 @@  static struct bpf_object *bpf_object__new(const char *path,
 	obj->efile.bss_shndx = -1;
 	obj->efile.st_ops_shndx = -1;
 	obj->kconfig_map_idx = -1;
+	obj->rodata_map_idx = -1;
 
 	obj->kern_version = get_kernel_version();
 	obj->loaded = false;
@@ -1428,6 +1432,8 @@  static int bpf_object__init_global_data_maps(struct bpf_object *obj)
 						    obj->efile.rodata->d_size);
 		if (err)
 			return err;
+
+		obj->rodata_map_idx = obj->nr_maps - 1;
 	}
 	if (obj->efile.bss_shndx >= 0) {
 		err = bpf_object__init_internal_map(obj, LIBBPF_MAP_BSS,
@@ -3729,18 +3735,13 @@  static int probe_kern_prog_name(void)
 	return probe_fd(ret);
 }
 
-static int probe_kern_global_data(void)
+static void probe_create_global_data(int *prog, int *map,
+				     struct bpf_insn *insns, size_t insns_cnt)
 {
 	struct bpf_load_program_attr prg_attr;
 	struct bpf_create_map_attr map_attr;
 	char *cp, errmsg[STRERR_BUFSIZE];
-	struct bpf_insn insns[] = {
-		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 16),
-		BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 42),
-		BPF_MOV64_IMM(BPF_REG_0, 0),
-		BPF_EXIT_INSN(),
-	};
-	int ret, map;
+	int err;
 
 	memset(&map_attr, 0, sizeof(map_attr));
 	map_attr.map_type = BPF_MAP_TYPE_ARRAY;
@@ -3748,26 +3749,40 @@  static int probe_kern_global_data(void)
 	map_attr.value_size = 32;
 	map_attr.max_entries = 1;
 
-	map = bpf_create_map_xattr(&map_attr);
-	if (map < 0) {
-		ret = -errno;
-		cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
+	*map = bpf_create_map_xattr(&map_attr);
+	if (*map < 0) {
+		err = errno;
+		cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
 		pr_warn("Error in %s():%s(%d). Couldn't create simple array map.\n",
-			__func__, cp, -ret);
-		return ret;
+			__func__, cp, -err);
+		return;
 	}
 
-	insns[0].imm = map;
+	insns[0].imm = *map;
 
 	memset(&prg_attr, 0, sizeof(prg_attr));
 	prg_attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
 	prg_attr.insns = insns;
-	prg_attr.insns_cnt = ARRAY_SIZE(insns);
+	prg_attr.insns_cnt = insns_cnt;
 	prg_attr.license = "GPL";
 
-	ret = bpf_load_program_xattr(&prg_attr, NULL, 0);
+	*prog = bpf_load_program_xattr(&prg_attr, NULL, 0);
+}
+
+static int probe_kern_global_data(void)
+{
+	struct bpf_insn insns[] = {
+		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 16),
+		BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 42),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	int prog = -1, map = -1;
+
+	probe_create_global_data(&prog, &map, insns, ARRAY_SIZE(insns));
+
 	close(map);
-	return probe_fd(ret);
+	return probe_fd(prog);
 }
 
 static int probe_kern_btf(void)
@@ -3894,6 +3909,32 @@  static int probe_kern_probe_read_kernel(void)
 	return probe_fd(bpf_load_program_xattr(&attr, NULL, 0));
 }
 
+static int probe_prog_bind_map(void)
+{
+	struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	int prog = -1, map = -1, ret = 0;
+
+	if (!kernel_supports(FEAT_GLOBAL_DATA))
+		return 0;
+
+	probe_create_global_data(&prog, &map, insns, ARRAY_SIZE(insns));
+
+	if (map >= 0 && prog < 0) {
+		close(map);
+		return 0;
+	}
+
+	if (!bpf_prog_bind_map(prog, map, NULL))
+		ret = 1;
+
+	close(map);
+	close(prog);
+	return ret;
+}
+
 enum kern_feature_result {
 	FEAT_UNKNOWN = 0,
 	FEAT_SUPPORTED = 1,
@@ -3934,6 +3975,9 @@  static struct kern_feature_desc {
 	},
 	[FEAT_PROBE_READ_KERN] = {
 		"bpf_probe_read_kernel() helper", probe_kern_probe_read_kernel,
+	},
+	[FEAT_PROG_BIND_MAP] = {
+		"BPF_PROG_BIND_MAP support", probe_prog_bind_map,
 	}
 };
 
@@ -6468,6 +6512,20 @@  load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 	if (ret >= 0) {
 		if (log_buf && load_attr.log_level)
 			pr_debug("verifier log:\n%s", log_buf);
+
+		if (prog->obj->rodata_map_idx >= 0 &&
+		    kernel_supports(FEAT_PROG_BIND_MAP)) {
+			struct bpf_map *rodata_map =
+				&prog->obj->maps[prog->obj->rodata_map_idx];
+
+			if (bpf_prog_bind_map(ret, bpf_map__fd(rodata_map), NULL)) {
+				cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+				pr_warn("prog '%s': failed to bind .rodata map: %s\n",
+					prog->name, cp);
+				/* Don't fail hard if can't bind rodata. */
+			}
+		}
+
 		*pfd = ret;
 		ret = 0;
 		goto out;
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 92ceb48a5ca2..0b7830f4ff8b 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -308,4 +308,5 @@  LIBBPF_0.2.0 {
 		perf_buffer__epoll_fd;
 		perf_buffer__consume_buffer;
 		xsk_socket__create_shared;
+		bpf_prog_bind_map;
 } LIBBPF_0.1.0;