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/*
* syscall_nt.c - checks syscalls with NT set
* Copyright (c) 2014-2015 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.
*
* Some obscure user-space code requires the ability to make system calls
* with FLAGS.NT set. Make sure it works.
*/
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <err.h>
#include <sys/syscall.h>
#include <asm/processor-flags.h>
#ifdef __x86_64__
# define WIDTH "q"
#else
# define WIDTH "l"
#endif
static unsigned int nerrs;
static unsigned long get_eflags(void)
{
unsigned long eflags;
asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
return eflags;
}
static void set_eflags(unsigned long eflags)
{
asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
: : "rm" (eflags) : "flags");
}
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 void sigtrap(int sig, siginfo_t *si, void *ctx_void)
{
}
static void do_it(unsigned long extraflags)
{
unsigned long flags;
set_eflags(get_eflags() | extraflags);
syscall(SYS_getpid);
flags = get_eflags();
set_eflags(X86_EFLAGS_IF | X86_EFLAGS_FIXED);
if ((flags & extraflags) == extraflags) {
printf("[OK]\tThe syscall worked and flags are still set\n");
} else {
printf("[FAIL]\tThe syscall worked but flags were cleared (flags = 0x%lx but expected 0x%lx set)\n",
flags, extraflags);
nerrs++;
}
}
int main(void)
{
printf("[RUN]\tSet NT and issue a syscall\n");
do_it(X86_EFLAGS_NT);
/*
* Now try it again with TF set -- TF forces returns via IRET in all
* cases except non-ptregs-using 64-bit full fast path syscalls.
*/
sethandler(SIGTRAP, sigtrap, 0);
printf("[RUN]\tSet NT|TF and issue a syscall\n");
do_it(X86_EFLAGS_NT | X86_EFLAGS_TF);
return nerrs == 0 ? 0 : 1;
}
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