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