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-rw-r--r--bpf_jit_disasm.c207
1 files changed, 207 insertions, 0 deletions
diff --git a/bpf_jit_disasm.c b/bpf_jit_disasm.c
new file mode 100644
index 0000000..6d1df6e
--- /dev/null
+++ b/bpf_jit_disasm.c
@@ -0,0 +1,207 @@
+/*
+ * Minimal BPF JIT image disassembler
+ *
+ * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
+ * debugging or verification purposes.
+ *
+ * There is no Makefile. Compile with
+ *
+ * `gcc -Wall -O2 bpf_jit_disasm.c -o bpf_jit_disasm -lopcodes -lbfd -ldl`
+ *
+ * or similar.
+ *
+ * To get the disassembly of the JIT code, do the following:
+ *
+ * 1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
+ * 2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
+ * 3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code
+ *
+ * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
+ * Licensed under the GNU General Public License, version 2.0 (GPLv2)
+ *
+ * Note: this is part of the Linux kernel and can be found under tools/net/.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <unistd.h>
+#include <string.h>
+#include <bfd.h>
+#include <dis-asm.h>
+#include <sys/klog.h>
+#include <sys/types.h>
+#include <regex.h>
+
+static void get_exec_path(char *tpath, size_t size)
+{
+ char *path;
+ ssize_t len;
+
+ snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
+ tpath[size - 1] = 0;
+
+ path = strdup(tpath);
+ assert(path);
+
+ len = readlink(path, tpath, size);
+ tpath[len] = 0;
+
+ free(path);
+}
+
+static void get_asm_insns(uint8_t *image, size_t len, unsigned long base,
+ int opcodes)
+{
+ int count, i, pc = 0;
+ char tpath[256];
+ struct disassemble_info info;
+ disassembler_ftype disassemble;
+ bfd *bfdf;
+
+ memset(tpath, 0, sizeof(tpath));
+ get_exec_path(tpath, sizeof(tpath));
+
+ bfdf = bfd_openr(tpath, NULL);
+ assert(bfdf);
+ assert(bfd_check_format(bfdf, bfd_object));
+
+ init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
+ info.arch = bfd_get_arch(bfdf);
+ info.mach = bfd_get_mach(bfdf);
+ info.buffer = image;
+ info.buffer_length = len;
+
+ disassemble_init_for_target(&info);
+
+ disassemble = disassembler(bfdf);
+ assert(disassemble);
+
+ do {
+ printf("%4x:\t", pc);
+
+ count = disassemble(pc, &info);
+
+ if (opcodes) {
+ printf("\n\t");
+ for (i = 0; i < count; ++i)
+ printf("%02x ", (uint8_t) image[pc + i]);
+ }
+ printf("\n");
+
+ pc += count;
+ } while(count > 0 && pc < len);
+
+ bfd_close(bfdf);
+}
+
+static char *get_klog_buff(int *klen)
+{
+ int ret, len = klogctl(10, NULL, 0);
+ char *buff = malloc(len);
+
+ assert(buff && klen);
+ ret = klogctl(3, buff, len);
+ assert(ret >= 0);
+ *klen = ret;
+
+ return buff;
+}
+
+static void put_klog_buff(char *buff)
+{
+ free(buff);
+}
+
+static int get_last_jit_image(char *haystack, size_t hlen,
+ uint8_t *image, size_t ilen,
+ unsigned long *base)
+{
+ char *ptr, *pptr, *tmp;
+ off_t off = 0;
+ int ret, flen, proglen, pass, ulen = 0;
+ regmatch_t pmatch[1];
+ regex_t regex;
+
+ if (hlen == 0)
+ return 0;
+
+ ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
+ "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
+ assert(ret == 0);
+
+ ptr = haystack;
+ while (1) {
+ ret = regexec(&regex, ptr, 1, pmatch, 0);
+ if (ret == 0) {
+ ptr += pmatch[0].rm_eo;
+ off += pmatch[0].rm_eo;
+ assert(off < hlen);
+ } else
+ break;
+ }
+
+ ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
+ ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
+ &flen, &proglen, &pass, base);
+ if (ret != 4)
+ return 0;
+
+ tmp = ptr = haystack + off;
+ while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
+ tmp = NULL;
+ if (!strstr(ptr, "JIT code"))
+ continue;
+ pptr = ptr;
+ while ((ptr = strstr(pptr, ":")))
+ pptr = ptr + 1;
+ ptr = pptr;
+ do {
+ image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
+ if (ptr == pptr || ulen >= ilen) {
+ ulen--;
+ break;
+ }
+ ptr = pptr;
+ } while (1);
+ }
+
+ assert(ulen == proglen);
+ printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
+ proglen, pass, flen);
+ printf("%lx + <x>:\n", *base);
+
+ regfree(&regex);
+ return ulen;
+}
+
+int main(int argc, char **argv)
+{
+ int len, klen, opcodes = 0;
+ char *kbuff;
+ unsigned long base;
+ uint8_t image[4096];
+
+ if (argc > 1) {
+ if (!strncmp("-o", argv[argc - 1], 2)) {
+ opcodes = 1;
+ } else {
+ printf("usage: bpf_jit_disasm [-o: show opcodes]\n");
+ exit(0);
+ }
+ }
+
+ bfd_init();
+ memset(image, 0, sizeof(image));
+
+ kbuff = get_klog_buff(&klen);
+
+ len = get_last_jit_image(kbuff, klen, image, sizeof(image), &base);
+ if (len > 0 && base > 0)
+ get_asm_insns(image, len, base, opcodes);
+
+ put_klog_buff(kbuff);
+
+ return 0;
+}