[PATCH RFC v3 net-next 1/3] samples: bpf: elf file loader

[Alexei Starovoitov]

simple .o parser and loader using BPF syscall.
.o is a standard ELF generated by LLVM backend

/* parses elf file compiled by llvm .c->.o
 * creates maps and stores FD into map_fd array
 * loads eBPF programs
 * returns zero on success
 */
int load_bpf_file(char *path);

Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
---
 samples/bpf/bpf_helpers.h |   21 +++++
 samples/bpf/bpf_load.c    |  228 +++++++++++++++++++++++++++++++++++++++++++++
 samples/bpf/bpf_load.h    |   18 ++++
 3 files changed, 267 insertions(+)
 create mode 100644 samples/bpf/bpf_helpers.h
 create mode 100644 samples/bpf/bpf_load.c
 create mode 100644 samples/bpf/bpf_load.h

diff --git a/samples/bpf/bpf_helpers.h b/samples/bpf/bpf_helpers.h
new file mode 100644
index 000000000000..356e7d34d174
--- /dev/null
+++ b/samples/bpf/bpf_helpers.h
@@ -0,0 +1,21 @@
+#ifndef __BPF_HELPERS_H
+#define __BPF_HELPERS_H
+
+#define SEC(NAME) __attribute__((section(NAME), used))
+
+static void *(*bpf_load_pointer)(void *unsafe_ptr) = (void *) BPF_FUNC_load_pointer;
+static int (*bpf_printk)(const char *fmt, int fmt_size, ...) = (void *) BPF_FUNC_printk;
+static int (*bpf_memcmp)(void *unsafe_ptr, void *safe_ptr, int size) = (void *) BPF_FUNC_memcmp;
+static void *(*bpf_map_lookup_elem)(void *map, void *key) = (void*) BPF_FUNC_map_lookup_elem;
+static int (*bpf_map_update_elem)(void *map, void *key, void *value) = (void*) BPF_FUNC_map_update_elem;
+static int (*bpf_map_delete_elem)(void *map, void *key) = (void *) BPF_FUNC_map_delete_elem;
+static void (*bpf_dump_stack)(void) = (void *) BPF_FUNC_dump_stack;
+
+struct bpf_map_def {
+	int type;
+	int key_size;
+	int value_size;
+	int max_entries;
+};
+
+#endif
diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
new file mode 100644
index 000000000000..7614f19d5282
--- /dev/null
+++ b/samples/bpf/bpf_load.c
@@ -0,0 +1,228 @@
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <libelf.h>
+#include <gelf.h>
+#include <errno.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdbool.h>
+#include <linux/bpf.h>
+#include "libbpf.h"
+#include "bpf_helpers.h"
+#include "bpf_load.h"
+
+#define DEBUGFS "/sys/kernel/debug/tracing/"
+
+static char license[128];
+static bool processed_sec[128];
+int map_fd[MAX_MAPS];
+
+static int load_and_attach(const char *event, char *prog, int size,
+			   const struct bpf_map_fixup *fixups, int fixup_len)
+{
+	int fd, event_fd, err;
+	char fmt[32];
+	char path[256] = DEBUGFS;
+
+	fd = bpf_prog_load(BPF_PROG_TYPE_TRACING_FILTER,
+			   (struct bpf_insn *)prog, size, license,
+			   fixups, fixup_len);
+
+	if (fd < 0) {
+		printf("err %d errno %d\n", fd, errno);
+		return fd;
+	}
+
+
+	snprintf(fmt, sizeof(fmt), "bpf-%d", fd);
+
+	strcat(path, event);
+	strcat(path, "/filter");
+
+	printf("writing %s -> %s\n", fmt, path);
+
+	event_fd = open(path, O_WRONLY, 0);
+	if (event_fd < 0) {
+		printf("failed to open event %s\n", event);
+		return event_fd;
+	}
+
+	err = write(event_fd, fmt, strlen(fmt));
+	(void) err;
+
+	return 0;
+}
+
+static int load_maps(struct bpf_map_def *maps, int len)
+{
+	int i;
+
+	for (i = 0; i < len / sizeof(struct bpf_map_def); i++) {
+
+		map_fd[i] = bpf_create_map(maps[i].type,
+					   maps[i].key_size,
+					   maps[i].value_size,
+					   maps[i].max_entries);
+		if (map_fd[i] < 0)
+			return 1;
+	}
+	return 0;
+}
+
+static int get_sec(Elf *elf, int i, GElf_Ehdr *ehdr, char **shname,
+		   GElf_Shdr *shdr, Elf_Data **data)
+{
+	Elf_Scn *scn;
+
+	scn = elf_getscn(elf, i);
+	if (!scn)
+		return 1;
+
+	if (gelf_getshdr(scn, shdr) != shdr)
+		return 2;
+
+	*shname = elf_strptr(elf, ehdr->e_shstrndx, shdr->sh_name);
+	if (!*shname || !shdr->sh_size)
+		return 3;
+
+	*data = elf_getdata(scn, 0);
+	if (!*data || elf_getdata(scn, *data) != NULL)
+		return 4;
+
+	return 0;
+}
+
+static struct bpf_map_fixup fixup[128];
+
+static int parse_relo_into_map_fixup(Elf_Data *data, Elf_Data *symbols,
+				     GElf_Shdr *shdr)
+{
+	GElf_Sym sym;
+	GElf_Rel rel;
+	int i, nrels;
+
+	nrels = shdr->sh_size / shdr->sh_entsize;
+
+	for (i = 0; i < nrels; i++) {
+		gelf_getrel(data, i, &rel);
+
+		fixup[i].insn_idx = rel.r_offset / sizeof(struct bpf_insn);
+
+		gelf_getsym(symbols, GELF_R_SYM(rel.r_info), &sym);
+
+		fixup[i].fd = map_fd[sym.st_value / sizeof(struct bpf_map_def)];
+	}
+
+	return nrels;
+}
+
+int load_bpf_file(char *path)
+{
+	int fd, i, nrels;
+	Elf *elf;
+	GElf_Ehdr ehdr;
+	GElf_Shdr shdr, shdr_prog;
+	Elf_Data *data, *data_prog, *symbols = NULL;
+	char *shname, *shname_prog;
+
+	if (elf_version(EV_CURRENT) == EV_NONE)
+		return 1;
+
+	fd = open(path, O_RDONLY, 0);
+	if (fd < 0)
+		return 1;
+
+	elf = elf_begin(fd, ELF_C_READ, NULL);
+
+	if (!elf)
+		return 1;
+
+	if (gelf_getehdr(elf, &ehdr) != &ehdr)
+		return 1;
+
+	/* scan over all elf sections to get license and map info */
+	for (i = 1; i < ehdr.e_shnum; i++) {
+
+		if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
+			continue;
+
+		if (0)
+			printf("section %d:%s data %p size %zd link %d flags %d\n",
+			       i, shname, data->d_buf, data->d_size,
+			       shdr.sh_link, (int) shdr.sh_flags);
+
+		if (strcmp(shname, "license") == 0) {
+			processed_sec[i] = true;
+			memcpy(license, data->d_buf, data->d_size);
+		} else if (strcmp(shname, "maps") == 0) {
+			processed_sec[i] = true;
+			if (load_maps(data->d_buf, data->d_size))
+				return 1;
+		} else if (shdr.sh_type == SHT_SYMTAB) {
+			symbols = data;
+		}
+	}
+
+	/* load programs that need map fixup (relocations) */
+	for (i = 1; i < ehdr.e_shnum; i++) {
+
+		if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
+			continue;
+		if (shdr.sh_type == SHT_REL) {
+
+			if (get_sec(elf, shdr.sh_info, &ehdr, &shname_prog,
+				    &shdr_prog, &data_prog))
+				continue;
+
+			if (0)
+				printf("relo %s into %s\n", shname, shname_prog);
+
+			processed_sec[shdr.sh_info] = true;
+			processed_sec[i] = true;
+
+			nrels = parse_relo_into_map_fixup(data, symbols, &shdr);
+
+			if (memcmp(shname_prog, "events/", sizeof("events/") - 1) == 0)
+				load_and_attach(shname_prog,
+						data_prog->d_buf, data_prog->d_size,
+						fixup, nrels * sizeof(fixup[0]));
+		}
+	}
+
+	/* load programs that don't use maps */
+	for (i = 1; i < ehdr.e_shnum; i++) {
+
+		if (processed_sec[i])
+			continue;
+
+		if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
+			continue;
+
+		if (memcmp(shname, "events/", sizeof("events/") - 1) == 0)
+			load_and_attach(shname, data->d_buf, data->d_size,
+					NULL, 0);
+	}
+
+	close(fd);
+	return 0;
+}
+
+void read_trace_pipe(void)
+{
+	int trace_fd;
+
+	trace_fd = open(DEBUGFS "trace_pipe", O_RDONLY, 0);
+	if (trace_fd < 0)
+		return;
+
+	while (1) {
+		static char buf[4096];
+		ssize_t sz;
+
+		sz = read(trace_fd, buf, sizeof(buf));
+		if (sz)
+			puts(buf);
+	}
+}
diff --git a/samples/bpf/bpf_load.h b/samples/bpf/bpf_load.h
new file mode 100644
index 000000000000..d34e61a101d2
--- /dev/null
+++ b/samples/bpf/bpf_load.h
@@ -0,0 +1,18 @@
+#ifndef __BPF_LOAD_H
+#define __BPF_LOAD_H
+
+#define MAX_MAPS 64
+
+extern int map_fd[MAX_MAPS];
+
+/* parses elf file compiled by llvm .c->.o
+ * creates maps and stores FD into map_fd array
+ * loads eBPF programs
+ * returns zero on success
+ */
+int load_bpf_file(char *path);
+
+/* forever reads /sys/.../trace_pipe */
+void read_trace_pipe(void);
+
+#endif
-- 
1.7.9.5

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