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@mina86
Last active November 26, 2021 15:00
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Code reading auxiliary vector present in executable binary.
#define _GNU_SOURCE
#include <linux/auxvec.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
static unsigned long *getauxv(void) {
char **env = environ;
while (*env++) {
/* nop */
}
return (void*)env;
}
struct aux_handler {
unsigned long key;
const char *name;
void (*handler)(const struct aux_handler *h, unsigned long *aux);
const char *desc, *arg;
};
static void handle_print(const struct aux_handler *h, unsigned long *aux) {
printf(h->arg, h->name, aux[0], aux[1], h->desc);
}
static void handle_random(const struct aux_handler *h, unsigned long *aux) {
const unsigned char *ch = (void *)aux[1], *end = ch + 16;
printf("%-16s %2lu ", h->name, aux[0]);
for (; ch != end; ++ch) {
printf("%02x", (unsigned)*ch);
}
printf(" // %s\n", h->desc);
}
#define AUX_HANDLER(key, handler, desc, arg) { key, #key, handler, desc, arg }
#define AUX_NUM(key, desc) { key, #key, handle_print, desc, "%-16s %2lu %-15lu // %s\n" }
#define AUX_HEX(key, desc) { key, #key, handle_print, desc, "%-16s %2lu 0x%-13lx // %s\n" }
#define AUX_STR(key, desc) { key, #key, handle_print, desc, "%-16s %2lu %-15s // %s\n" }
static const struct aux_handler aux_handlers[] = {
AUX_HANDLER(AT_IGNORE, NULL, NULL, NULL),
AUX_HANDLER(AT_RANDOM, handle_random, "16 random bytes", NULL),
AUX_NUM(AT_EXECFD, "file descriptor of program"),
AUX_HEX(AT_PHDR, "program headers for program"),
AUX_NUM(AT_PHENT, "size of program header entry"),
AUX_NUM(AT_PHNUM, "number of program headers"),
AUX_NUM(AT_PAGESZ, "system page size"),
AUX_HEX(AT_BASE, "base address of interpreter"),
AUX_HEX(AT_FLAGS, "flags"),
AUX_HEX(AT_ENTRY, "entry point of program"),
AUX_NUM(AT_NOTELF, "program is not ELF"),
AUX_NUM(AT_UID, "real uid"),
AUX_NUM(AT_EUID, "effective uid"),
AUX_NUM(AT_GID, "real gid"),
AUX_NUM(AT_EGID, "effective gid"),
AUX_STR(AT_PLATFORM, "CPU identity for optimizations"),
AUX_HEX(AT_HWCAP, "hints at CPU capabilities"),
AUX_HEX(AT_HWCAP2, "further hints at CPU capabilities"),
AUX_NUM(AT_CLKTCK, "frequency at which times() increments"),
AUX_NUM(AT_SECURE, "secure mode boolean"),
AUX_STR(AT_BASE_PLATFORM, "string identifying real platform"),
AUX_STR(AT_EXECFN, "filename of program"),
#ifdef AT_DCACHEBSIZE
AUX_NUM(AT_DCACHEBSIZE, "data cache block size"),
#endif
#ifdef AT_ICACHEBSIZE
AUX_NUM(AT_ICACHEBSIZE, "instruction cache block size"),
#endif
#ifdef AT_UCACHEBSIZE
AUX_NUM(AT_UCACHEBSIZE, "unified cache block size"),
#endif
#ifdef AT_L1D_CACHEGEOMETRY
AUX_HEX(AT_L1D_CACHEGEOMETRY, "L1 data cache geometry"),
#endif
#ifdef AT_L1D_CACHESIZE
AUX_NUM(AT_L1D_CACHESIZE, "L1 data cache size"),
#endif
#ifdef AT_L1I_CACHEGEOMETRY
AUX_HEX(AT_L1I_CACHEGEOMETRY, "L1 inst. cache geometry"),
#endif
#ifdef AT_L1I_CACHESIZE
AUX_NUM(AT_L1I_CACHESIZE, "L1 inst. cache size"),
#endif
#ifdef AT_L2_CACHEGEOMETRY
AUX_HEX(AT_L2_CACHEGEOMETRY, "L2 cache geometry"),
#endif
#ifdef AT_L2_CACHESIZE
AUX_NUM(AT_L2_CACHESIZE, "L2 cache size"),
#endif
#ifdef AT_L3_CACHEGEOMETRY
AUX_HEX(AT_L3_CACHEGEOMETRY, "L3 cache geometry"),
#endif
#ifdef AT_L3_CACHESIZE
AUX_NUM(AT_L3_CACHESIZE, "L3 cache size"),
#endif
#ifdef AT_FPUCW
AUX_NUM(AT_FPUCW, "used FPU control word"),
#endif
#ifdef AT_SYSINFO
AUX_HEX(AT_SYSINFO, "entry point to syscall in the vDSO"),
#endif
#ifdef AT_SYSINFO_EHDR
AUX_HEX(AT_SYSINFO_EHDR, "address of vDSO page"),
#endif
{ AT_NULL, "(unknown)", handle_print,
"unknown field", "%-16s %2lu %-15lu\n" }
};
#undef AUX_HANDLER
#undef AUX_NUM
#undef AUX_STR
int main() {
unsigned long *auxv = getauxv(), key;
const struct aux_handler *h;
while (*auxv != AT_NULL) {
h = aux_handlers;
key = *auxv;
while (h->key != key && h->key != AT_NULL) {
++h;
}
if (h->handler) {
h->handler(h, auxv);
}
auxv += 2;
}
return 0;
}
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