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-rw-r--r--linux-user/qemu.h50
-rw-r--r--linux-user/signal.c163
-rw-r--r--linux-user/syscall.c73
3 files changed, 213 insertions, 73 deletions
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index f09b750bbf..5138289bfb 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -123,14 +123,33 @@ typedef struct TaskState {
#endif
uint32_t stack_base;
int used; /* non zero if used */
- bool sigsegv_blocked; /* SIGSEGV blocked by guest */
struct image_info *info;
struct linux_binprm *bprm;
struct emulated_sigtable sigtab[TARGET_NSIG];
struct sigqueue sigqueue_table[MAX_SIGQUEUE_SIZE]; /* siginfo queue */
struct sigqueue *first_free; /* first free siginfo queue entry */
- int signal_pending; /* non zero if a signal may be pending */
+ /* This thread's signal mask, as requested by the guest program.
+ * The actual signal mask of this thread may differ:
+ * + we don't let SIGSEGV and SIGBUS be blocked while running guest code
+ * + sometimes we block all signals to avoid races
+ */
+ sigset_t signal_mask;
+ /* The signal mask imposed by a guest sigsuspend syscall, if we are
+ * currently in the middle of such a syscall
+ */
+ sigset_t sigsuspend_mask;
+ /* Nonzero if we're leaving a sigsuspend and sigsuspend_mask is valid. */
+ int in_sigsuspend;
+
+ /* Nonzero if process_pending_signals() needs to do something (either
+ * handle a pending signal or unblock signals).
+ * This flag is written from a signal handler so should be accessed via
+ * the atomic_read() and atomic_write() functions. (It is not accessed
+ * from multiple threads.)
+ */
+ int signal_pending;
+
} __attribute__((aligned(16))) TaskState;
extern char *exec_path;
@@ -235,6 +254,12 @@ unsigned long init_guest_space(unsigned long host_start,
* It's also OK to implement these with safe_syscall, though it will be
* a little less efficient if a signal is delivered at the 'wrong' moment.
*
+ * Some non-interruptible syscalls need to be handled using block_signals()
+ * to block signals for the duration of the syscall. This mainly applies
+ * to code which needs to modify the data structures used by the
+ * host_signal_handler() function and the functions it calls, including
+ * all syscalls which change the thread's signal mask.
+ *
* (2) Interruptible syscalls
*
* These are guest syscalls that can be interrupted by signals and
@@ -266,6 +291,8 @@ unsigned long init_guest_space(unsigned long host_start,
* you make in the implementation returns either -TARGET_ERESTARTSYS or
* EINTR though.)
*
+ * block_signals() cannot be used for interruptible syscalls.
+ *
*
* How and why the safe_syscall implementation works:
*
@@ -352,6 +379,25 @@ long do_sigreturn(CPUArchState *env);
long do_rt_sigreturn(CPUArchState *env);
abi_long do_sigaltstack(abi_ulong uss_addr, abi_ulong uoss_addr, abi_ulong sp);
int do_sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
+/**
+ * block_signals: block all signals while handling this guest syscall
+ *
+ * Block all signals, and arrange that the signal mask is returned to
+ * its correct value for the guest before we resume execution of guest code.
+ * If this function returns non-zero, then the caller should immediately
+ * return -TARGET_ERESTARTSYS to the main loop, which will take the pending
+ * signal and restart execution of the syscall.
+ * If block_signals() returns zero, then the caller can continue with
+ * emulation of the system call knowing that no signals can be taken
+ * (and therefore that no race conditions will result).
+ * This should only be called once, because if it is called a second time
+ * it will always return non-zero. (Think of it like a mutex that can't
+ * be recursively locked.)
+ * Signals will be unblocked again by process_pending_signals().
+ *
+ * Return value: non-zero if there was a pending signal, zero if not.
+ */
+int block_signals(void); /* Returns non zero if signal pending */
#ifdef TARGET_I386
/* vm86.c */
diff --git a/linux-user/signal.c b/linux-user/signal.c
index 1b86a8550c..a89853d4eb 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -190,61 +190,81 @@ void target_to_host_old_sigset(sigset_t *sigset,
target_to_host_sigset(sigset, &d);
}
+int block_signals(void)
+{
+ TaskState *ts = (TaskState *)thread_cpu->opaque;
+ sigset_t set;
+ int pending;
+
+ /* It's OK to block everything including SIGSEGV, because we won't
+ * run any further guest code before unblocking signals in
+ * process_pending_signals().
+ */
+ sigfillset(&set);
+ sigprocmask(SIG_SETMASK, &set, 0);
+
+ pending = atomic_xchg(&ts->signal_pending, 1);
+
+ return pending;
+}
+
/* Wrapper for sigprocmask function
* Emulates a sigprocmask in a safe way for the guest. Note that set and oldset
- * are host signal set, not guest ones. This wraps the sigprocmask host calls
- * that should be protected (calls originated from guest)
+ * are host signal set, not guest ones. Returns -TARGET_ERESTARTSYS if
+ * a signal was already pending and the syscall must be restarted, or
+ * 0 on success.
+ * If set is NULL, this is guaranteed not to fail.
*/
int do_sigprocmask(int how, const sigset_t *set, sigset_t *oldset)
{
- int ret;
- sigset_t val;
- sigset_t *temp = NULL;
- CPUState *cpu = thread_cpu;
- TaskState *ts = (TaskState *)cpu->opaque;
- bool segv_was_blocked = ts->sigsegv_blocked;
+ TaskState *ts = (TaskState *)thread_cpu->opaque;
+
+ if (oldset) {
+ *oldset = ts->signal_mask;
+ }
if (set) {
- bool has_sigsegv = sigismember(set, SIGSEGV);
- val = *set;
- temp = &val;
+ int i;
- sigdelset(temp, SIGSEGV);
+ if (block_signals()) {
+ return -TARGET_ERESTARTSYS;
+ }
switch (how) {
case SIG_BLOCK:
- if (has_sigsegv) {
- ts->sigsegv_blocked = true;
- }
+ sigorset(&ts->signal_mask, &ts->signal_mask, set);
break;
case SIG_UNBLOCK:
- if (has_sigsegv) {
- ts->sigsegv_blocked = false;
+ for (i = 1; i <= NSIG; ++i) {
+ if (sigismember(set, i)) {
+ sigdelset(&ts->signal_mask, i);
+ }
}
break;
case SIG_SETMASK:
- ts->sigsegv_blocked = has_sigsegv;
+ ts->signal_mask = *set;
break;
default:
g_assert_not_reached();
}
- }
-
- ret = sigprocmask(how, temp, oldset);
- if (oldset && segv_was_blocked) {
- sigaddset(oldset, SIGSEGV);
+ /* Silently ignore attempts to change blocking status of KILL or STOP */
+ sigdelset(&ts->signal_mask, SIGKILL);
+ sigdelset(&ts->signal_mask, SIGSTOP);
}
-
- return ret;
+ return 0;
}
#if !defined(TARGET_OPENRISC) && !defined(TARGET_UNICORE32) && \
!defined(TARGET_X86_64)
-/* Just set the guest's signal mask to the specified value */
+/* Just set the guest's signal mask to the specified value; the
+ * caller is assumed to have called block_signals() already.
+ */
static void set_sigmask(const sigset_t *set)
{
- do_sigprocmask(SIG_SETMASK, set, NULL);
+ TaskState *ts = (TaskState *)thread_cpu->opaque;
+
+ ts->signal_mask = *set;
}
#endif
@@ -376,6 +396,7 @@ static int core_dump_signal(int sig)
void signal_init(void)
{
+ TaskState *ts = (TaskState *)thread_cpu->opaque;
struct sigaction act;
struct sigaction oact;
int i, j;
@@ -391,6 +412,9 @@ void signal_init(void)
target_to_host_signal_table[j] = i;
}
+ /* Set the signal mask from the host mask. */
+ sigprocmask(0, 0, &ts->signal_mask);
+
/* set all host signal handlers. ALL signals are blocked during
the handlers to serialize them. */
memset(sigact_table, 0, sizeof(sigact_table));
@@ -509,7 +533,7 @@ int queue_signal(CPUArchState *env, int sig, target_siginfo_t *info)
queue = gdb_queuesig ();
handler = sigact_table[sig - 1]._sa_handler;
- if (ts->sigsegv_blocked && sig == TARGET_SIGSEGV) {
+ if (sig == TARGET_SIGSEGV && sigismember(&ts->signal_mask, SIGSEGV)) {
/* Guest has blocked SIGSEGV but we got one anyway. Assume this
* is a forced SIGSEGV (ie one the kernel handles via force_sig_info
* because it got a real MMU fault). A blocked SIGSEGV in that
@@ -565,7 +589,7 @@ int queue_signal(CPUArchState *env, int sig, target_siginfo_t *info)
q->next = NULL;
k->pending = 1;
/* signal that a new signal is pending */
- ts->signal_pending = 1;
+ atomic_set(&ts->signal_pending, 1);
return 1; /* indicates that the signal was queued */
}
}
@@ -583,6 +607,7 @@ static void host_signal_handler(int host_signum, siginfo_t *info,
CPUArchState *env = thread_cpu->env_ptr;
int sig;
target_siginfo_t tinfo;
+ ucontext_t *uc = puc;
/* the CPU emulator uses some host signals to detect exceptions,
we forward to it some signals */
@@ -602,6 +627,16 @@ static void host_signal_handler(int host_signum, siginfo_t *info,
host_to_target_siginfo_noswap(&tinfo, info);
if (queue_signal(env, sig, &tinfo) == 1) {
+ /* Block host signals until target signal handler entered. We
+ * can't block SIGSEGV or SIGBUS while we're executing guest
+ * code in case the guest code provokes one in the window between
+ * now and it getting out to the main loop. Signals will be
+ * unblocked again in process_pending_signals().
+ */
+ sigfillset(&uc->uc_sigmask);
+ sigdelset(&uc->uc_sigmask, SIGSEGV);
+ sigdelset(&uc->uc_sigmask, SIGBUS);
+
/* interrupt the virtual CPU as soon as possible */
cpu_exit(thread_cpu);
}
@@ -2673,9 +2708,13 @@ void sparc64_get_context(CPUSPARCState *env)
env->pc = env->npc;
env->npc += 4;
- err = 0;
-
- do_sigprocmask(0, NULL, &set);
+ /* If we're only reading the signal mask then do_sigprocmask()
+ * is guaranteed not to fail, which is important because we don't
+ * have any way to signal a failure or restart this operation since
+ * this is not a normal syscall.
+ */
+ err = do_sigprocmask(0, NULL, &set);
+ assert(err == 0);
host_to_target_sigset_internal(&target_set, &set);
if (TARGET_NSIG_WORDS == 1) {
__put_user(target_set.sig[0],
@@ -5778,7 +5817,7 @@ static void handle_pending_signal(CPUArchState *cpu_env, int sig)
{
CPUState *cpu = ENV_GET_CPU(cpu_env);
abi_ulong handler;
- sigset_t set, old_set;
+ sigset_t set;
target_sigset_t target_old_set;
struct target_sigaction *sa;
struct sigqueue *q;
@@ -5801,7 +5840,7 @@ static void handle_pending_signal(CPUArchState *cpu_env, int sig)
handler = sa->_sa_handler;
}
- if (ts->sigsegv_blocked && sig == TARGET_SIGSEGV) {
+ if (sig == TARGET_SIGSEGV && sigismember(&ts->signal_mask, SIGSEGV)) {
/* Guest has blocked SIGSEGV but we got one anyway. Assume this
* is a forced SIGSEGV (ie one the kernel handles via force_sig_info
* because it got a real MMU fault), and treat as if default handler.
@@ -5825,17 +5864,23 @@ static void handle_pending_signal(CPUArchState *cpu_env, int sig)
force_sig(sig);
} else {
/* compute the blocked signals during the handler execution */
+ sigset_t *blocked_set;
+
target_to_host_sigset(&set, &sa->sa_mask);
/* SA_NODEFER indicates that the current signal should not be
blocked during the handler */
if (!(sa->sa_flags & TARGET_SA_NODEFER))
sigaddset(&set, target_to_host_signal(sig));
- /* block signals in the handler using Linux */
- do_sigprocmask(SIG_BLOCK, &set, &old_set);
/* save the previous blocked signal state to restore it at the
end of the signal execution (see do_sigreturn) */
- host_to_target_sigset_internal(&target_old_set, &old_set);
+ host_to_target_sigset_internal(&target_old_set, &ts->signal_mask);
+
+ /* block signals in the handler */
+ blocked_set = ts->in_sigsuspend ?
+ &ts->sigsuspend_mask : &ts->signal_mask;
+ sigorset(&ts->signal_mask, blocked_set, &set);
+ ts->in_sigsuspend = 0;
/* if the CPU is in VM86 mode, we restore the 32 bit values */
#if defined(TARGET_I386) && !defined(TARGET_X86_64)
@@ -5869,18 +5914,38 @@ void process_pending_signals(CPUArchState *cpu_env)
CPUState *cpu = ENV_GET_CPU(cpu_env);
int sig;
TaskState *ts = cpu->opaque;
+ sigset_t set;
+ sigset_t *blocked_set;
- if (!ts->signal_pending)
- return;
-
- /* FIXME: This is not threadsafe. */
- for(sig = 1; sig <= TARGET_NSIG; sig++) {
- if (ts->sigtab[sig - 1].pending) {
- handle_pending_signal(cpu_env, sig);
- return;
+ while (atomic_read(&ts->signal_pending)) {
+ /* FIXME: This is not threadsafe. */
+ sigfillset(&set);
+ sigprocmask(SIG_SETMASK, &set, 0);
+
+ for (sig = 1; sig <= TARGET_NSIG; sig++) {
+ blocked_set = ts->in_sigsuspend ?
+ &ts->sigsuspend_mask : &ts->signal_mask;
+
+ if (ts->sigtab[sig - 1].pending &&
+ (!sigismember(blocked_set,
+ target_to_host_signal_table[sig])
+ || sig == TARGET_SIGSEGV)) {
+ handle_pending_signal(cpu_env, sig);
+ /* Restart scan from the beginning */
+ sig = 1;
+ }
}
- }
- /* if no signal is pending, just return */
- ts->signal_pending = 0;
- return;
+
+ /* if no signal is pending, unblock signals and recheck (the act
+ * of unblocking might cause us to take another host signal which
+ * will set signal_pending again).
+ */
+ atomic_set(&ts->signal_pending, 0);
+ ts->in_sigsuspend = 0;
+ set = ts->signal_mask;
+ sigdelset(&set, SIGSEGV);
+ sigdelset(&set, SIGBUS);
+ sigprocmask(SIG_SETMASK, &set, 0);
+ }
+ ts->in_sigsuspend = 0;
}
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 083f26ff3e..5a346425d6 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -4746,6 +4746,7 @@ static int do_fork(CPUArchState *env, unsigned int flags, abi_ulong newsp,
new_cpu->opaque = ts;
ts->bprm = parent_ts->bprm;
ts->info = parent_ts->info;
+ ts->signal_mask = parent_ts->signal_mask;
nptl_flags = flags;
flags &= ~CLONE_NPTL_FLAGS2;
@@ -6841,9 +6842,11 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
{
sigset_t cur_set;
abi_ulong target_set;
- do_sigprocmask(0, NULL, &cur_set);
- host_to_target_old_sigset(&target_set, &cur_set);
- ret = target_set;
+ ret = do_sigprocmask(0, NULL, &cur_set);
+ if (!ret) {
+ host_to_target_old_sigset(&target_set, &cur_set);
+ ret = target_set;
+ }
}
break;
#endif
@@ -6852,12 +6855,20 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
{
sigset_t set, oset, cur_set;
abi_ulong target_set = arg1;
- do_sigprocmask(0, NULL, &cur_set);
+ /* We only have one word of the new mask so we must read
+ * the rest of it with do_sigprocmask() and OR in this word.
+ * We are guaranteed that a do_sigprocmask() that only queries
+ * the signal mask will not fail.
+ */
+ ret = do_sigprocmask(0, NULL, &cur_set);
+ assert(!ret);
target_to_host_old_sigset(&set, &target_set);
sigorset(&set, &set, &cur_set);
- do_sigprocmask(SIG_SETMASK, &set, &oset);
- host_to_target_old_sigset(&target_set, &oset);
- ret = target_set;
+ ret = do_sigprocmask(SIG_SETMASK, &set, &oset);
+ if (!ret) {
+ host_to_target_old_sigset(&target_set, &oset);
+ ret = target_set;
+ }
}
break;
#endif
@@ -6886,7 +6897,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
mask = arg2;
target_to_host_old_sigset(&set, &mask);
- ret = get_errno(do_sigprocmask(how, &set, &oldset));
+ ret = do_sigprocmask(how, &set, &oldset);
if (!is_error(ret)) {
host_to_target_old_sigset(&mask, &oldset);
ret = mask;
@@ -6920,7 +6931,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
how = 0;
set_ptr = NULL;
}
- ret = get_errno(do_sigprocmask(how, set_ptr, &oldset));
+ ret = do_sigprocmask(how, set_ptr, &oldset);
if (!is_error(ret) && arg3) {
if (!(p = lock_user(VERIFY_WRITE, arg3, sizeof(target_sigset_t), 0)))
goto efault;
@@ -6960,7 +6971,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
how = 0;
set_ptr = NULL;
}
- ret = get_errno(do_sigprocmask(how, set_ptr, &oldset));
+ ret = do_sigprocmask(how, set_ptr, &oldset);
if (!is_error(ret) && arg3) {
if (!(p = lock_user(VERIFY_WRITE, arg3, sizeof(target_sigset_t), 0)))
goto efault;
@@ -6998,28 +7009,36 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
#ifdef TARGET_NR_sigsuspend
case TARGET_NR_sigsuspend:
{
- sigset_t set;
+ TaskState *ts = cpu->opaque;
#if defined(TARGET_ALPHA)
abi_ulong mask = arg1;
- target_to_host_old_sigset(&set, &mask);
+ target_to_host_old_sigset(&ts->sigsuspend_mask, &mask);
#else
if (!(p = lock_user(VERIFY_READ, arg1, sizeof(target_sigset_t), 1)))
goto efault;
- target_to_host_old_sigset(&set, p);
+ target_to_host_old_sigset(&ts->sigsuspend_mask, p);
unlock_user(p, arg1, 0);
#endif
- ret = get_errno(safe_rt_sigsuspend(&set, SIGSET_T_SIZE));
+ ret = get_errno(safe_rt_sigsuspend(&ts->sigsuspend_mask,
+ SIGSET_T_SIZE));
+ if (ret != -TARGET_ERESTARTSYS) {
+ ts->in_sigsuspend = 1;
+ }
}
break;
#endif
case TARGET_NR_rt_sigsuspend:
{
- sigset_t set;
+ TaskState *ts = cpu->opaque;
if (!(p = lock_user(VERIFY_READ, arg1, sizeof(target_sigset_t), 1)))
goto efault;
- target_to_host_sigset(&set, p);
+ target_to_host_sigset(&ts->sigsuspend_mask, p);
unlock_user(p, arg1, 0);
- ret = get_errno(safe_rt_sigsuspend(&set, SIGSET_T_SIZE));
+ ret = get_errno(safe_rt_sigsuspend(&ts->sigsuspend_mask,
+ SIGSET_T_SIZE));
+ if (ret != -TARGET_ERESTARTSYS) {
+ ts->in_sigsuspend = 1;
+ }
}
break;
case TARGET_NR_rt_sigtimedwait:
@@ -7065,11 +7084,19 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
break;
#ifdef TARGET_NR_sigreturn
case TARGET_NR_sigreturn:
- ret = do_sigreturn(cpu_env);
+ if (block_signals()) {
+ ret = -TARGET_ERESTARTSYS;
+ } else {
+ ret = do_sigreturn(cpu_env);
+ }
break;
#endif
case TARGET_NR_rt_sigreturn:
- ret = do_rt_sigreturn(cpu_env);
+ if (block_signals()) {
+ ret = -TARGET_ERESTARTSYS;
+ } else {
+ ret = do_rt_sigreturn(cpu_env);
+ }
break;
case TARGET_NR_sethostname:
if (!(p = lock_user_string(arg1)))
@@ -9123,9 +9150,11 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
}
mask = arg2;
target_to_host_old_sigset(&set, &mask);
- do_sigprocmask(how, &set, &oldset);
- host_to_target_old_sigset(&mask, &oldset);
- ret = mask;
+ ret = do_sigprocmask(how, &set, &oldset);
+ if (!ret) {
+ host_to_target_old_sigset(&mask, &oldset);
+ ret = mask;
+ }
}
break;
#endif
generated by cgit v1.2.3 (git 2.25.1) at 2024-04-25 04:27:41 +0000