qemu/util/main-loop.c
Daniele Buono c905a3680d cfi: Initial support for cfi-icall in QEMU
LLVM/Clang, supports runtime checks for forward-edge Control-Flow
Integrity (CFI).

CFI on indirect function calls (cfi-icall) ensures that, in indirect
function calls, the function called is of the right signature for the
pointer type defined at compile time.

For this check to work, the code must always respect the function
signature when using function pointer, the function must be defined
at compile time, and be compiled with link-time optimization.

This rules out, for example, shared libraries that are dynamically loaded
(given that functions are not known at compile time), and code that is
dynamically generated at run-time.

This patch:

1) Introduces the CONFIG_CFI flag to support cfi in QEMU

2) Introduces a decorator to allow the definition of "sensitive"
functions, where a non-instrumented function may be called at runtime
through a pointer. The decorator will take care of disabling cfi-icall
checks on such functions, when cfi is enabled.

3) Marks functions currently in QEMU that exhibit such behavior,
in particular:
- The function in TCG that calls pre-compiled TBs
- The function in TCI that interprets instructions
- Functions in the plugin infrastructures that jump to callbacks
- Functions in util that directly call a signal handler

Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org
Message-Id: <20201204230615.2392-3-dbuono@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2021-01-02 21:03:35 +01:00

656 lines
17 KiB
C

/*
* QEMU System Emulator
*
* Copyright (c) 2003-2008 Fabrice Bellard
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu/osdep.h"
#include "qapi/error.h"
#include "qemu/cutils.h"
#include "qemu/timer.h"
#include "sysemu/qtest.h"
#include "sysemu/cpu-timers.h"
#include "sysemu/replay.h"
#include "qemu/main-loop.h"
#include "block/aio.h"
#include "qemu/error-report.h"
#include "qemu/queue.h"
#include "qemu/compiler.h"
#ifndef _WIN32
#include <sys/wait.h>
#endif
#ifndef _WIN32
/* If we have signalfd, we mask out the signals we want to handle and then
* use signalfd to listen for them. We rely on whatever the current signal
* handler is to dispatch the signals when we receive them.
*/
/*
* Disable CFI checks.
* We are going to call a signal hander directly. Such handler may or may not
* have been defined in our binary, so there's no guarantee that the pointer
* used to set the handler is a cfi-valid pointer. Since the handlers are
* stored in kernel memory, changing the handler to an attacker-defined
* function requires being able to call a sigaction() syscall,
* which is not as easy as overwriting a pointer in memory.
*/
QEMU_DISABLE_CFI
static void sigfd_handler(void *opaque)
{
int fd = (intptr_t)opaque;
struct qemu_signalfd_siginfo info;
struct sigaction action;
ssize_t len;
while (1) {
do {
len = read(fd, &info, sizeof(info));
} while (len == -1 && errno == EINTR);
if (len == -1 && errno == EAGAIN) {
break;
}
if (len != sizeof(info)) {
error_report("read from sigfd returned %zd: %s", len,
g_strerror(errno));
return;
}
sigaction(info.ssi_signo, NULL, &action);
if ((action.sa_flags & SA_SIGINFO) && action.sa_sigaction) {
sigaction_invoke(&action, &info);
} else if (action.sa_handler) {
action.sa_handler(info.ssi_signo);
}
}
}
static int qemu_signal_init(Error **errp)
{
int sigfd;
sigset_t set;
/*
* SIG_IPI must be blocked in the main thread and must not be caught
* by sigwait() in the signal thread. Otherwise, the cpu thread will
* not catch it reliably.
*/
sigemptyset(&set);
sigaddset(&set, SIG_IPI);
sigaddset(&set, SIGIO);
sigaddset(&set, SIGALRM);
sigaddset(&set, SIGBUS);
/* SIGINT cannot be handled via signalfd, so that ^C can be used
* to interrupt QEMU when it is being run under gdb. SIGHUP and
* SIGTERM are also handled asynchronously, even though it is not
* strictly necessary, because they use the same handler as SIGINT.
*/
pthread_sigmask(SIG_BLOCK, &set, NULL);
sigdelset(&set, SIG_IPI);
sigfd = qemu_signalfd(&set);
if (sigfd == -1) {
error_setg_errno(errp, errno, "failed to create signalfd");
return -errno;
}
fcntl_setfl(sigfd, O_NONBLOCK);
qemu_set_fd_handler(sigfd, sigfd_handler, NULL, (void *)(intptr_t)sigfd);
return 0;
}
#else /* _WIN32 */
static int qemu_signal_init(Error **errp)
{
return 0;
}
#endif
static AioContext *qemu_aio_context;
static QEMUBH *qemu_notify_bh;
static void notify_event_cb(void *opaque)
{
/* No need to do anything; this bottom half is only used to
* kick the kernel out of ppoll/poll/WaitForMultipleObjects.
*/
}
AioContext *qemu_get_aio_context(void)
{
return qemu_aio_context;
}
void qemu_notify_event(void)
{
if (!qemu_aio_context) {
return;
}
qemu_bh_schedule(qemu_notify_bh);
}
static GArray *gpollfds;
int qemu_init_main_loop(Error **errp)
{
int ret;
GSource *src;
init_clocks(qemu_timer_notify_cb);
ret = qemu_signal_init(errp);
if (ret) {
return ret;
}
qemu_aio_context = aio_context_new(errp);
if (!qemu_aio_context) {
return -EMFILE;
}
qemu_notify_bh = qemu_bh_new(notify_event_cb, NULL);
gpollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
src = aio_get_g_source(qemu_aio_context);
g_source_set_name(src, "aio-context");
g_source_attach(src, NULL);
g_source_unref(src);
src = iohandler_get_g_source();
g_source_set_name(src, "io-handler");
g_source_attach(src, NULL);
g_source_unref(src);
return 0;
}
static int max_priority;
#ifndef _WIN32
static int glib_pollfds_idx;
static int glib_n_poll_fds;
void qemu_fd_register(int fd)
{
}
static void glib_pollfds_fill(int64_t *cur_timeout)
{
GMainContext *context = g_main_context_default();
int timeout = 0;
int64_t timeout_ns;
int n;
g_main_context_prepare(context, &max_priority);
glib_pollfds_idx = gpollfds->len;
n = glib_n_poll_fds;
do {
GPollFD *pfds;
glib_n_poll_fds = n;
g_array_set_size(gpollfds, glib_pollfds_idx + glib_n_poll_fds);
pfds = &g_array_index(gpollfds, GPollFD, glib_pollfds_idx);
n = g_main_context_query(context, max_priority, &timeout, pfds,
glib_n_poll_fds);
} while (n != glib_n_poll_fds);
if (timeout < 0) {
timeout_ns = -1;
} else {
timeout_ns = (int64_t)timeout * (int64_t)SCALE_MS;
}
*cur_timeout = qemu_soonest_timeout(timeout_ns, *cur_timeout);
}
static void glib_pollfds_poll(void)
{
GMainContext *context = g_main_context_default();
GPollFD *pfds = &g_array_index(gpollfds, GPollFD, glib_pollfds_idx);
if (g_main_context_check(context, max_priority, pfds, glib_n_poll_fds)) {
g_main_context_dispatch(context);
}
}
#define MAX_MAIN_LOOP_SPIN (1000)
static int os_host_main_loop_wait(int64_t timeout)
{
GMainContext *context = g_main_context_default();
int ret;
g_main_context_acquire(context);
glib_pollfds_fill(&timeout);
qemu_mutex_unlock_iothread();
replay_mutex_unlock();
ret = qemu_poll_ns((GPollFD *)gpollfds->data, gpollfds->len, timeout);
replay_mutex_lock();
qemu_mutex_lock_iothread();
glib_pollfds_poll();
g_main_context_release(context);
return ret;
}
#else
/***********************************************************/
/* Polling handling */
typedef struct PollingEntry {
PollingFunc *func;
void *opaque;
struct PollingEntry *next;
} PollingEntry;
static PollingEntry *first_polling_entry;
int qemu_add_polling_cb(PollingFunc *func, void *opaque)
{
PollingEntry **ppe, *pe;
pe = g_malloc0(sizeof(PollingEntry));
pe->func = func;
pe->opaque = opaque;
for(ppe = &first_polling_entry; *ppe != NULL; ppe = &(*ppe)->next);
*ppe = pe;
return 0;
}
void qemu_del_polling_cb(PollingFunc *func, void *opaque)
{
PollingEntry **ppe, *pe;
for(ppe = &first_polling_entry; *ppe != NULL; ppe = &(*ppe)->next) {
pe = *ppe;
if (pe->func == func && pe->opaque == opaque) {
*ppe = pe->next;
g_free(pe);
break;
}
}
}
/***********************************************************/
/* Wait objects support */
typedef struct WaitObjects {
int num;
int revents[MAXIMUM_WAIT_OBJECTS + 1];
HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS + 1];
void *opaque[MAXIMUM_WAIT_OBJECTS + 1];
} WaitObjects;
static WaitObjects wait_objects = {0};
int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
{
WaitObjects *w = &wait_objects;
if (w->num >= MAXIMUM_WAIT_OBJECTS) {
return -1;
}
w->events[w->num] = handle;
w->func[w->num] = func;
w->opaque[w->num] = opaque;
w->revents[w->num] = 0;
w->num++;
return 0;
}
void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
{
int i, found;
WaitObjects *w = &wait_objects;
found = 0;
for (i = 0; i < w->num; i++) {
if (w->events[i] == handle) {
found = 1;
}
if (found) {
w->events[i] = w->events[i + 1];
w->func[i] = w->func[i + 1];
w->opaque[i] = w->opaque[i + 1];
w->revents[i] = w->revents[i + 1];
}
}
if (found) {
w->num--;
}
}
void qemu_fd_register(int fd)
{
WSAEventSelect(fd, event_notifier_get_handle(&qemu_aio_context->notifier),
FD_READ | FD_ACCEPT | FD_CLOSE |
FD_CONNECT | FD_WRITE | FD_OOB);
}
static int pollfds_fill(GArray *pollfds, fd_set *rfds, fd_set *wfds,
fd_set *xfds)
{
int nfds = -1;
int i;
for (i = 0; i < pollfds->len; i++) {
GPollFD *pfd = &g_array_index(pollfds, GPollFD, i);
int fd = pfd->fd;
int events = pfd->events;
if (events & G_IO_IN) {
FD_SET(fd, rfds);
nfds = MAX(nfds, fd);
}
if (events & G_IO_OUT) {
FD_SET(fd, wfds);
nfds = MAX(nfds, fd);
}
if (events & G_IO_PRI) {
FD_SET(fd, xfds);
nfds = MAX(nfds, fd);
}
}
return nfds;
}
static void pollfds_poll(GArray *pollfds, int nfds, fd_set *rfds,
fd_set *wfds, fd_set *xfds)
{
int i;
for (i = 0; i < pollfds->len; i++) {
GPollFD *pfd = &g_array_index(pollfds, GPollFD, i);
int fd = pfd->fd;
int revents = 0;
if (FD_ISSET(fd, rfds)) {
revents |= G_IO_IN;
}
if (FD_ISSET(fd, wfds)) {
revents |= G_IO_OUT;
}
if (FD_ISSET(fd, xfds)) {
revents |= G_IO_PRI;
}
pfd->revents = revents & pfd->events;
}
}
static int os_host_main_loop_wait(int64_t timeout)
{
GMainContext *context = g_main_context_default();
GPollFD poll_fds[1024 * 2]; /* this is probably overkill */
int select_ret = 0;
int g_poll_ret, ret, i, n_poll_fds;
PollingEntry *pe;
WaitObjects *w = &wait_objects;
gint poll_timeout;
int64_t poll_timeout_ns;
static struct timeval tv0;
fd_set rfds, wfds, xfds;
int nfds;
g_main_context_acquire(context);
/* XXX: need to suppress polling by better using win32 events */
ret = 0;
for (pe = first_polling_entry; pe != NULL; pe = pe->next) {
ret |= pe->func(pe->opaque);
}
if (ret != 0) {
g_main_context_release(context);
return ret;
}
FD_ZERO(&rfds);
FD_ZERO(&wfds);
FD_ZERO(&xfds);
nfds = pollfds_fill(gpollfds, &rfds, &wfds, &xfds);
if (nfds >= 0) {
select_ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv0);
if (select_ret != 0) {
timeout = 0;
}
if (select_ret > 0) {
pollfds_poll(gpollfds, nfds, &rfds, &wfds, &xfds);
}
}
g_main_context_prepare(context, &max_priority);
n_poll_fds = g_main_context_query(context, max_priority, &poll_timeout,
poll_fds, ARRAY_SIZE(poll_fds));
g_assert(n_poll_fds + w->num <= ARRAY_SIZE(poll_fds));
for (i = 0; i < w->num; i++) {
poll_fds[n_poll_fds + i].fd = (DWORD_PTR)w->events[i];
poll_fds[n_poll_fds + i].events = G_IO_IN;
}
if (poll_timeout < 0) {
poll_timeout_ns = -1;
} else {
poll_timeout_ns = (int64_t)poll_timeout * (int64_t)SCALE_MS;
}
poll_timeout_ns = qemu_soonest_timeout(poll_timeout_ns, timeout);
qemu_mutex_unlock_iothread();
replay_mutex_unlock();
g_poll_ret = qemu_poll_ns(poll_fds, n_poll_fds + w->num, poll_timeout_ns);
replay_mutex_lock();
qemu_mutex_lock_iothread();
if (g_poll_ret > 0) {
for (i = 0; i < w->num; i++) {
w->revents[i] = poll_fds[n_poll_fds + i].revents;
}
for (i = 0; i < w->num; i++) {
if (w->revents[i] && w->func[i]) {
w->func[i](w->opaque[i]);
}
}
}
if (g_main_context_check(context, max_priority, poll_fds, n_poll_fds)) {
g_main_context_dispatch(context);
}
g_main_context_release(context);
return select_ret || g_poll_ret;
}
#endif
static NotifierList main_loop_poll_notifiers =
NOTIFIER_LIST_INITIALIZER(main_loop_poll_notifiers);
void main_loop_poll_add_notifier(Notifier *notify)
{
notifier_list_add(&main_loop_poll_notifiers, notify);
}
void main_loop_poll_remove_notifier(Notifier *notify)
{
notifier_remove(notify);
}
void main_loop_wait(int nonblocking)
{
MainLoopPoll mlpoll = {
.state = MAIN_LOOP_POLL_FILL,
.timeout = UINT32_MAX,
.pollfds = gpollfds,
};
int ret;
int64_t timeout_ns;
if (nonblocking) {
mlpoll.timeout = 0;
}
/* poll any events */
g_array_set_size(gpollfds, 0); /* reset for new iteration */
/* XXX: separate device handlers from system ones */
notifier_list_notify(&main_loop_poll_notifiers, &mlpoll);
if (mlpoll.timeout == UINT32_MAX) {
timeout_ns = -1;
} else {
timeout_ns = (uint64_t)mlpoll.timeout * (int64_t)(SCALE_MS);
}
timeout_ns = qemu_soonest_timeout(timeout_ns,
timerlistgroup_deadline_ns(
&main_loop_tlg));
ret = os_host_main_loop_wait(timeout_ns);
mlpoll.state = ret < 0 ? MAIN_LOOP_POLL_ERR : MAIN_LOOP_POLL_OK;
notifier_list_notify(&main_loop_poll_notifiers, &mlpoll);
if (icount_enabled()) {
/*
* CPU thread can infinitely wait for event after
* missing the warp
*/
icount_start_warp_timer();
}
qemu_clock_run_all_timers();
}
/* Functions to operate on the main QEMU AioContext. */
QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)
{
return aio_bh_new(qemu_aio_context, cb, opaque);
}
/*
* Functions to operate on the I/O handler AioContext.
* This context runs on top of main loop. We can't reuse qemu_aio_context
* because iohandlers mustn't be polled by aio_poll(qemu_aio_context).
*/
static AioContext *iohandler_ctx;
static void iohandler_init(void)
{
if (!iohandler_ctx) {
iohandler_ctx = aio_context_new(&error_abort);
}
}
AioContext *iohandler_get_aio_context(void)
{
iohandler_init();
return iohandler_ctx;
}
GSource *iohandler_get_g_source(void)
{
iohandler_init();
return aio_get_g_source(iohandler_ctx);
}
void qemu_set_fd_handler(int fd,
IOHandler *fd_read,
IOHandler *fd_write,
void *opaque)
{
iohandler_init();
aio_set_fd_handler(iohandler_ctx, fd, false,
fd_read, fd_write, NULL, opaque);
}
void event_notifier_set_handler(EventNotifier *e,
EventNotifierHandler *handler)
{
iohandler_init();
aio_set_event_notifier(iohandler_ctx, e, false,
handler, NULL);
}
/* reaping of zombies. right now we're not passing the status to
anyone, but it would be possible to add a callback. */
#ifndef _WIN32
typedef struct ChildProcessRecord {
int pid;
QLIST_ENTRY(ChildProcessRecord) next;
} ChildProcessRecord;
static QLIST_HEAD(, ChildProcessRecord) child_watches =
QLIST_HEAD_INITIALIZER(child_watches);
static QEMUBH *sigchld_bh;
static void sigchld_handler(int signal)
{
qemu_bh_schedule(sigchld_bh);
}
static void sigchld_bh_handler(void *opaque)
{
ChildProcessRecord *rec, *next;
QLIST_FOREACH_SAFE(rec, &child_watches, next, next) {
if (waitpid(rec->pid, NULL, WNOHANG) == rec->pid) {
QLIST_REMOVE(rec, next);
g_free(rec);
}
}
}
static void qemu_init_child_watch(void)
{
struct sigaction act;
sigchld_bh = qemu_bh_new(sigchld_bh_handler, NULL);
memset(&act, 0, sizeof(act));
act.sa_handler = sigchld_handler;
act.sa_flags = SA_NOCLDSTOP;
sigaction(SIGCHLD, &act, NULL);
}
int qemu_add_child_watch(pid_t pid)
{
ChildProcessRecord *rec;
if (!sigchld_bh) {
qemu_init_child_watch();
}
QLIST_FOREACH(rec, &child_watches, next) {
if (rec->pid == pid) {
return 1;
}
}
rec = g_malloc0(sizeof(ChildProcessRecord));
rec->pid = pid;
QLIST_INSERT_HEAD(&child_watches, rec, next);
return 0;
}
#endif