cregit-Linux how code gets into the kernel

Release 4.7 tools/net/bpf_jit_disasm.c

Directory: tools/net
/*
 * Minimal BPF JIT image disassembler
 *
 * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
 * debugging or verification purposes.
 *
 * 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)
 */

#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 <regex.h>
#include <fcntl.h>
#include <sys/klog.h>
#include <sys/types.h>
#include <sys/stat.h>


#define CMD_ACTION_SIZE_BUFFER		10

#define CMD_ACTION_READ_ALL		3


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); }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann79100.00%1100.00%
Total79100.00%1100.00%


static void get_asm_insns(uint8_t *image, size_t len, 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); }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann233100.00%1100.00%
Total233100.00%1100.00%


static char *get_klog_buff(unsigned int *klen) { int ret, len; char *buff; len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0); if (len < 0) return NULL; buff = malloc(len); if (!buff) return NULL; ret = klogctl(CMD_ACTION_READ_ALL, buff, len); if (ret < 0) { free(buff); return NULL; } *klen = ret; return buff; }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann8290.11%266.67%
colin kingcolin king99.89%133.33%
Total91100.00%3100.00%


static char *get_flog_buff(const char *file, unsigned int *klen) { int fd, ret, len; struct stat fi; char *buff; fd = open(file, O_RDONLY); if (fd < 0) return NULL; ret = fstat(fd, &fi); if (ret < 0 || !S_ISREG(fi.st_mode)) goto out; len = fi.st_size + 1; buff = malloc(len); if (!buff) goto out; memset(buff, 0, len); ret = read(fd, buff, len - 1); if (ret <= 0) goto out_free; close(fd); *klen = ret; return buff; out_free: free(buff); out: close(fd); return NULL; }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann161100.00%2100.00%
Total161100.00%2100.00%


static char *get_log_buff(const char *file, unsigned int *klen) { return file ? get_flog_buff(file, klen) : get_klog_buff(klen); }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann32100.00%1100.00%
Total32100.00%1100.00%


static void put_log_buff(char *buff) { free(buff); }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann15100.00%2100.00%
Total15100.00%2100.00%


static unsigned int get_last_jit_image(char *haystack, size_t hlen, uint8_t *image, size_t ilen) { char *ptr, *pptr, *tmp; off_t off = 0; int ret, flen, proglen, pass, ulen = 0; regmatch_t pmatch[1]; unsigned long base; 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; memset(pmatch, 0, sizeof(pmatch)); 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) { regfree(&regex); 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; }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann37098.40%360.00%
alexei starovoitovalexei starovoitov51.33%120.00%
andrzej hajdaandrzej hajda10.27%120.00%
Total376100.00%5100.00%


static void usage(void) { printf("Usage: bpf_jit_disasm [...]\n"); printf(" -o Also display related opcodes (default: off).\n"); printf(" -f <file> Read last image dump from file or stdin (default: klog).\n"); printf(" -h Display this help.\n"); }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann28100.00%1100.00%
Total28100.00%1100.00%


int main(int argc, char **argv) { unsigned int len, klen, opt, opcodes = 0; static uint8_t image[32768]; char *kbuff, *file = NULL; while ((opt = getopt(argc, argv, "of:")) != -1) { switch (opt) { case 'o': opcodes = 1; break; case 'f': file = optarg; break; default: usage(); return -1; } } bfd_init(); memset(image, 0, sizeof(image)); kbuff = get_log_buff(file, &klen); if (!kbuff) { fprintf(stderr, "Could not retrieve log buffer!\n"); return -1; } len = get_last_jit_image(kbuff, klen, image, sizeof(image)); if (len > 0) get_asm_insns(image, len, opcodes); else fprintf(stderr, "No JIT image found!\n"); put_log_buff(kbuff); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann17998.90%266.67%
alexei starovoitovalexei starovoitov21.10%133.33%
Total181100.00%3100.00%


Overall Contributors

PersonTokensPropCommitsCommitProp
daniel borkmanndaniel borkmann122798.63%342.86%
colin kingcolin king90.72%114.29%
alexei starovoitovalexei starovoitov70.56%228.57%
andrzej hajdaandrzej hajda10.08%114.29%
Total1244100.00%7100.00%
Directory: tools/net
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