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Handling interrupts with signals on Linux
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#include <stdio.h> | |
#include <stdlib.h> // exit | |
#include <string.h> // memset | |
#include <unistd.h> // sleep | |
#include <signal.h> | |
// Enum for when the program is 32 bits | |
// Source: https://sites.uclouvain.be/SystInfo/usr/include/sys/ucontext.h.html | |
enum | |
{ | |
REG_GS = 0, | |
REG_FS, | |
REG_ES, | |
REG_DS, | |
REG_EDI, | |
REG_ESI, | |
REG_EBP, | |
REG_ESP, | |
REG_EBX, | |
REG_EDX, | |
REG_ECX, | |
REG_EAX, | |
REG_TRAPNO, | |
REG_ERR, | |
REG_EIP, | |
REG_CS, | |
REG_EFL, | |
REG_UESP, | |
REG_SS | |
}; | |
/* | |
// Enum for when the program is 64 bits | |
// Source: https://code.woboq.org/userspace/glibc/sysdeps/unix/sysv/linux/x86/sys/ucontext.h.html | |
enum | |
{ | |
REG_R8 = 0, | |
REG_R9, | |
REG_R10, | |
REG_R11, | |
REG_R12, | |
REG_R13, | |
REG_R14, | |
REG_R15, | |
REG_RDI, | |
REG_RSI, | |
REG_RBP, | |
REG_RBX, | |
REG_RDX, | |
REG_RAX, | |
REG_RCX, | |
REG_RSP, | |
REG_RIP, | |
REG_EFL, | |
REG_CSGSFS, // Actually short cs, gs, fs, __pad0. | |
REG_ERR, | |
REG_TRAPNO, | |
REG_OLDMASK, | |
REG_CR2 | |
};*/ | |
int count = 0; | |
void dumpbytes(unsigned char *data, int count) | |
{ | |
int i; | |
printf("\n"); | |
for (i = 0; i < count; i++) | |
{ | |
if (i % 16 == 0) | |
{ | |
printf("\n"); | |
} | |
printf("%02X ", data[i]); | |
} | |
printf("\n\n"); | |
} | |
// http://courses.cms.caltech.edu/cs124/lectures-wi2016/CS124Lec15.pdf | |
void singal_handler(int sig, siginfo_t *sinfo, void *ctxt) | |
{ | |
count++; | |
ucontext_t *context = (ucontext_t *)ctxt; | |
// https://github.molgen.mpg.de/git-mirror/glibc/blob/master/sysdeps/unix/sysv/linux/x86/sys/ucontext.h#L152 | |
printf("EAX: %X\n", context->uc_mcontext.gregs[REG_EAX]); | |
printf("EBX: %X\n", context->uc_mcontext.gregs[REG_EBX]); | |
printf("ECX: %X\n", context->uc_mcontext.gregs[REG_ECX]); | |
printf("EDX: %X\n", context->uc_mcontext.gregs[REG_EDX]); | |
printf("ESI: %X\n", context->uc_mcontext.gregs[REG_ESI]); | |
printf("EDI: %X\n", context->uc_mcontext.gregs[REG_EDI]); | |
printf("EBP: %X\n", context->uc_mcontext.gregs[REG_EBP]); | |
printf("ESP: %X\n", context->uc_mcontext.gregs[REG_ESP]); | |
// address of instruction that triggered the signal | |
printf("EIP: %X\n", context->uc_mcontext.gregs[REG_EIP]); | |
sleep(1); | |
printf("±±±±±±±±±±±±±±±±±±±±±±±±±±±±\n"); | |
if (count >= 3) { | |
// Dump a few bytes | |
dumpbytes(context->uc_mcontext.gregs[REG_EIP], 32); | |
// Skip over the 2 bytes that caused the interrupt | |
context->uc_mcontext.gregs[REG_EIP] += 2; | |
} | |
} | |
int main() | |
{ | |
struct sigaction act; | |
memset(&act, 0, sizeof(struct sigaction)); | |
sigemptyset(&act.sa_mask); | |
act.sa_sigaction = singal_handler; | |
act.sa_flags = SA_SIGINFO; | |
if (sigaction(SIGSEGV, &act, NULL) < 0) | |
{ | |
printf("sigaction() error! couldn't set handler."); | |
exit(1); | |
} | |
printf("hello world\n"); | |
// interrupt, causes a segmentation fault | |
asm(".byte 0xCD"); | |
asm(".byte 0xFF"); | |
printf("skipped the bytes\n"); | |
sleep(1); | |
return 0; | |
} |
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