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| -rw-r--r-- | bpf_jit_disasm.c | 207 |
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(®ex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ " + "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED); + assert(ret == 0); + + ptr = haystack; + while (1) { + ret = regexec(®ex, 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(®ex); + 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; +} |