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/*
* entry_from_vm86.c - tests kernel entries from vm86 mode
* Copyright (c) 2014-2015 Andrew Lutomirski
*
* This exercises a few paths that need to special-case vm86 mode.
*
* GPL v2.
*/
#define _GNU_SOURCE
#include <assert.h>
#include <stdlib.h>
#include <sys/syscall.h>
#include <sys/signal.h>
#include <sys/ucontext.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include <sys/mman.h>
#include <err.h>
#include <stddef.h>
#include <stdbool.h>
#include <errno.h>
#include <sys/vm86.h>
static unsigned long load_addr = 0x10000;
static int nerrs = 0;
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 clearhandler(int sig)
{
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_handler = SIG_DFL;
sigemptyset(&sa.sa_mask);
if (sigaction(sig, &sa, 0))
err(1, "sigaction");
}
static sig_atomic_t got_signal;
static void sighandler(int sig, siginfo_t *info, void *ctx_void)
{
ucontext_t *ctx = (ucontext_t*)ctx_void;
if (ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_VM ||
(ctx->uc_mcontext.gregs[REG_CS] & 3) != 3) {
printf("[FAIL]\tSignal frame should not reflect vm86 mode\n");
nerrs++;
}
const char *signame;
if (sig == SIGSEGV)
signame = "SIGSEGV";
else if (sig == SIGILL)
signame = "SIGILL";
else
signame = "unexpected signal";
printf("[INFO]\t%s: FLAGS = 0x%lx, CS = 0x%hx\n", signame,
(unsigned long)ctx->uc_mcontext.gregs[REG_EFL],
(unsigned short)ctx->uc_mcontext.gregs[REG_CS]);
got_signal = 1;
}
asm (
".pushsection .rodata\n\t"
".type vmcode_bound, @object\n\t"
"vmcode:\n\t"
"vmcode_bound:\n\t"
".code16\n\t"
"bound %ax, (2048)\n\t"
"int3\n\t"
"vmcode_sysenter:\n\t"
"sysenter\n\t"
"vmcode_syscall:\n\t"
"syscall\n\t"
"vmcode_sti:\n\t"
"sti\n\t"
"vmcode_int3:\n\t"
"int3\n\t"
"vmcode_int80:\n\t"
"int $0x80\n\t"
".size vmcode, . - vmcode\n\t"
"end_vmcode:\n\t"
".code32\n\t"
".popsection"
);
extern unsigned char vmcode[], end_vmcode[];
extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
vmcode_sti[], vmcode_int3[], vmcode_int80[];
/* Returns false if the test was skipped. */
static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
unsigned int rettype, unsigned int retarg,
const char *text)
{
long ret;
printf("[RUN]\t%s from vm86 mode\n", text);
v86->regs.eip = eip;
ret = vm86(VM86_ENTER, v86);
if (ret == -1 && (errno == ENOSYS || errno == EPERM)) {
printf("[SKIP]\tvm86 %s\n",
errno == ENOSYS ? "not supported" : "not allowed");
return false;
}
if (VM86_TYPE(ret) == VM86_INTx) {
char trapname[32];
int trapno = VM86_ARG(ret);
if (trapno == 13)
strcpy(trapname, "GP");
else if (trapno == 5)
strcpy(trapname, "BR");
else if (trapno == 14)
strcpy(trapname, "PF");
else
sprintf(trapname, "%d", trapno);
printf("[INFO]\tExited vm86 mode due to #%s\n", trapname);
} else if (VM86_TYPE(ret) == VM86_UNKNOWN) {
printf("[INFO]\tExited vm86 mode due to unhandled GP fault\n");
} else if (VM86_TYPE(ret) == VM86_TRAP) {
printf("[INFO]\tExited vm86 mode due to a trap (arg=%ld)\n",
VM86_ARG(ret));
} else if (VM86_TYPE(ret) == VM86_SIGNAL) {
printf("[INFO]\tExited vm86 mode due to a signal\n");
} else if (VM86_TYPE(ret) == VM86_STI) {
printf("[INFO]\tExited vm86 mode due to STI\n");
} else {
printf("[INFO]\tExited vm86 mode due to type %ld, arg %ld\n",
VM86_TYPE(ret), VM86_ARG(ret));
}
if (rettype == -1 ||
(VM86_TYPE(ret) == rettype && VM86_ARG(ret) == retarg)) {
printf("[OK]\tReturned correctly\n");
} else {
printf("[FAIL]\tIncorrect return reason\n");
nerrs++;
}
return true;
}
int main(void)
{
struct vm86plus_struct v86;
unsigned char *addr = mmap((void *)load_addr, 4096,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_ANONYMOUS | MAP_PRIVATE, -1,0);
if (addr != (unsigned char *)load_addr)
err(1, "mmap");
memcpy(addr, vmcode, end_vmcode - vmcode);
addr[2048] = 2;
addr[2050] = 3;
memset(&v86, 0, sizeof(v86));
v86.regs.cs = load_addr / 16;
v86.regs.ss = load_addr / 16;
v86.regs.ds = load_addr / 16;
v86.regs.es = load_addr / 16;
assert((v86.regs.cs & 3) == 0); /* Looks like RPL = 0 */
/* #BR -- should deliver SIG??? */
do_test(&v86, vmcode_bound - vmcode, VM86_INTx, 5, "#BR");
/*
* SYSENTER -- should cause #GP or #UD depending on CPU.
* Expected return type -1 means that we shouldn't validate
* the vm86 return value. This will avoid problems on non-SEP
* CPUs.
*/
sethandler(SIGILL, sighandler, 0);
do_test(&v86, vmcode_sysenter - vmcode, -1, 0, "SYSENTER");
clearhandler(SIGILL);
/*
* SYSCALL would be a disaster in VM86 mode. Fortunately,
* there is no kernel that both enables SYSCALL and sets
* EFER.SCE, so it's #UD on all systems. But vm86 is
* buggy (or has a "feature"), so the SIGILL will actually
* be delivered.
*/
sethandler(SIGILL, sighandler, 0);
do_test(&v86, vmcode_syscall - vmcode, VM86_SIGNAL, 0, "SYSCALL");
clearhandler(SIGILL);
/* STI with VIP set */
v86.regs.eflags |= X86_EFLAGS_VIP;
v86.regs.eflags &= ~X86_EFLAGS_IF;
do_test(&v86, vmcode_sti - vmcode, VM86_STI, 0, "STI with VIP set");
/* INT3 -- should cause #BP */
do_test(&v86, vmcode_int3 - vmcode, VM86_TRAP, 3, "INT3");
/* INT80 -- should exit with "INTx 0x80" */
v86.regs.eax = (unsigned int)-1;
do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
/* Execute a null pointer */
v86.regs.cs = 0;
v86.regs.ss = 0;
sethandler(SIGSEGV, sighandler, 0);
got_signal = 0;
if (do_test(&v86, 0, VM86_SIGNAL, 0, "Execute null pointer") &&
!got_signal) {
printf("[FAIL]\tDid not receive SIGSEGV\n");
nerrs++;
}
clearhandler(SIGSEGV);
/* Make sure nothing explodes if we fork. */
if (fork() > 0)
return 0;
return (nerrs == 0 ? 0 : 1);
}
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