// SPDX-License-Identifier: GPL-2.0-only /* * syscall_nt.c - checks syscalls with NT set * Copyright (c) 2014-2015 Andrew Lutomirski * * 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 "helpers.h" static unsigned int nerrs; 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); printf("[RUN]\tSet AC and issue a syscall\n"); do_it(X86_EFLAGS_AC); printf("[RUN]\tSet NT|AC and issue a syscall\n"); do_it(X86_EFLAGS_NT | X86_EFLAGS_AC); /* * 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 TF and issue a syscall\n"); do_it(X86_EFLAGS_TF); printf("[RUN]\tSet NT|TF and issue a syscall\n"); do_it(X86_EFLAGS_NT | X86_EFLAGS_TF); printf("[RUN]\tSet AC|TF and issue a syscall\n"); do_it(X86_EFLAGS_AC | X86_EFLAGS_TF); printf("[RUN]\tSet NT|AC|TF and issue a syscall\n"); do_it(X86_EFLAGS_NT | X86_EFLAGS_AC | X86_EFLAGS_TF); /* * Now try DF. This is evil and it's plausible that we will crash * glibc, but glibc would have to do something rather surprising * for this to happen. */ printf("[RUN]\tSet DF and issue a syscall\n"); do_it(X86_EFLAGS_DF); printf("[RUN]\tSet TF|DF and issue a syscall\n"); do_it(X86_EFLAGS_TF | X86_EFLAGS_DF); return nerrs == 0 ? 0 : 1; }