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