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/*
* syscall_arg_fault.c - tests faults 32-bit fast syscall stack args
* Copyright (c) 2015 Andrew Lutomirski
*
* This program is free software; you can redistribute it and/or modify
* it under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*/
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/signal.h>
#include <sys/ucontext.h>
#include <err.h>
#include <setjmp.h>
#include <errno.h>
/* Our sigaltstack scratch space. */
static unsigned char altstack_data[SIGSTKSZ];
static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
int flags)
{
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_sigaction = handler;
sa.sa_flags = SA_SIGINFO | flags;
sigemptyset(&sa.sa_mask);
if (sigaction(sig, &sa, 0))
err(1, "sigaction");
}
static volatile sig_atomic_t sig_traps;
static sigjmp_buf jmpbuf;
static volatile sig_atomic_t n_errs;
static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
{
ucontext_t *ctx = (ucontext_t*)ctx_void;
if (ctx->uc_mcontext.gregs[REG_EAX] != -EFAULT) {
printf("[FAIL]\tAX had the wrong value: 0x%x\n",
ctx->uc_mcontext.gregs[REG_EAX]);
n_errs++;
} else {
printf("[OK]\tSeems okay\n");
}
siglongjmp(jmpbuf, 1);
}
static void sigill(int sig, siginfo_t *info, void *ctx_void)
{
printf("[SKIP]\tIllegal instruction\n");
siglongjmp(jmpbuf, 1);
}
int main()
{
stack_t stack = {
.ss_sp = altstack_data,
.ss_size = SIGSTKSZ,
};
if (sigaltstack(&stack, NULL) != 0)
err(1, "sigaltstack");
sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
/*
* The actual exception can vary. On Atom CPUs, we get #SS
* instead of #PF when the vDSO fails to access the stack when
* ESP is too close to 2^32, and #SS causes SIGBUS.
*/
sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
sethandler(SIGILL, sigill, SA_ONSTACK);
/*
* Exercise another nasty special case. The 32-bit SYSCALL
* and SYSENTER instructions (even in compat mode) each
* clobber one register. A Linux system call has a syscall
* number and six arguments, and the user stack pointer
* needs to live in some register on return. That means
* that we need eight registers, but SYSCALL and SYSENTER
* only preserve seven registers. As a result, one argument
* ends up on the stack. The stack is user memory, which
* means that the kernel can fail to read it.
*
* The 32-bit fast system calls don't have a defined ABI:
* we're supposed to invoke them through the vDSO. So we'll
* fudge it: we set all regs to invalid pointer values and
* invoke the entry instruction. The return will fail no
* matter what, and we completely lose our program state,
* but we can fix it up with a signal handler.
*/
printf("[RUN]\tSYSENTER with invalid state\n");
if (sigsetjmp(jmpbuf, 1) == 0) {
asm volatile (
"movl $-1, %%eax\n\t"
"movl $-1, %%ebx\n\t"
"movl $-1, %%ecx\n\t"
"movl $-1, %%edx\n\t"
"movl $-1, %%esi\n\t"
"movl $-1, %%edi\n\t"
"movl $-1, %%ebp\n\t"
"movl $-1, %%esp\n\t"
"sysenter"
: : : "memory", "flags");
}
printf("[RUN]\tSYSCALL with invalid state\n");
if (sigsetjmp(jmpbuf, 1) == 0) {
asm volatile (
"movl $-1, %%eax\n\t"
"movl $-1, %%ebx\n\t"
"movl $-1, %%ecx\n\t"
"movl $-1, %%edx\n\t"
"movl $-1, %%esi\n\t"
"movl $-1, %%edi\n\t"
"movl $-1, %%ebp\n\t"
"movl $-1, %%esp\n\t"
"syscall\n\t"
"pushl $0" /* make sure we segfault cleanly */
: : : "memory", "flags");
}
return 0;
}
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