linux/arch/um/os-Linux/signal.c
Richard Weinberger 57a05d83b1 um: Fix possible deadlock in sig_handler_common()
We are in atomic context and must not sleep.
Sleeping here is possible since malloc() maps
to kmalloc() with GFP_KERNEL.

Cc: stable@vger.kernel.org
Fixes: b6024b21 ("um: extend fpstate to _xstate to support YMM registers")
Signed-off-by: Richard Weinberger <richard@nod.at>
2016-08-04 00:17:58 +02:00

347 lines
7.5 KiB
C

/*
* Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
* Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
* Copyright (C) 2004 PathScale, Inc
* Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
* Licensed under the GPL
*/
#include <stdlib.h>
#include <stdarg.h>
#include <errno.h>
#include <signal.h>
#include <strings.h>
#include <as-layout.h>
#include <kern_util.h>
#include <os.h>
#include <sysdep/mcontext.h>
#include <um_malloc.h>
void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
[SIGTRAP] = relay_signal,
[SIGFPE] = relay_signal,
[SIGILL] = relay_signal,
[SIGWINCH] = winch,
[SIGBUS] = bus_handler,
[SIGSEGV] = segv_handler,
[SIGIO] = sigio_handler,
[SIGALRM] = timer_handler
};
static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
{
struct uml_pt_regs *r;
int save_errno = errno;
r = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
if (!r)
panic("out of memory");
r->is_user = 0;
if (sig == SIGSEGV) {
/* For segfaults, we want the data from the sigcontext. */
get_regs_from_mc(r, mc);
GET_FAULTINFO_FROM_MC(r->faultinfo, mc);
}
/* enable signals if sig isn't IRQ signal */
if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
unblock_signals();
(*sig_info[sig])(sig, si, r);
errno = save_errno;
free(r);
}
/*
* These are the asynchronous signals. SIGPROF is excluded because we want to
* be able to profile all of UML, not just the non-critical sections. If
* profiling is not thread-safe, then that is not my problem. We can disable
* profiling when SMP is enabled in that case.
*/
#define SIGIO_BIT 0
#define SIGIO_MASK (1 << SIGIO_BIT)
#define SIGALRM_BIT 1
#define SIGALRM_MASK (1 << SIGALRM_BIT)
static int signals_enabled;
static unsigned int signals_pending;
static unsigned int signals_active = 0;
void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
{
int enabled;
enabled = signals_enabled;
if (!enabled && (sig == SIGIO)) {
signals_pending |= SIGIO_MASK;
return;
}
block_signals();
sig_handler_common(sig, si, mc);
set_signals(enabled);
}
static void timer_real_alarm_handler(mcontext_t *mc)
{
struct uml_pt_regs *regs;
regs = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
if (!regs)
panic("out of memory");
if (mc != NULL)
get_regs_from_mc(regs, mc);
timer_handler(SIGALRM, NULL, regs);
free(regs);
}
void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
{
int enabled;
enabled = signals_enabled;
if (!signals_enabled) {
signals_pending |= SIGALRM_MASK;
return;
}
block_signals();
signals_active |= SIGALRM_MASK;
timer_real_alarm_handler(mc);
signals_active &= ~SIGALRM_MASK;
set_signals(enabled);
}
void deliver_alarm(void) {
timer_alarm_handler(SIGALRM, NULL, NULL);
}
void timer_set_signal_handler(void)
{
set_handler(SIGALRM);
}
void set_sigstack(void *sig_stack, int size)
{
stack_t stack = {
.ss_flags = 0,
.ss_sp = sig_stack,
.ss_size = size - sizeof(void *)
};
if (sigaltstack(&stack, NULL) != 0)
panic("enabling signal stack failed, errno = %d\n", errno);
}
static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
[SIGSEGV] = sig_handler,
[SIGBUS] = sig_handler,
[SIGILL] = sig_handler,
[SIGFPE] = sig_handler,
[SIGTRAP] = sig_handler,
[SIGIO] = sig_handler,
[SIGWINCH] = sig_handler,
[SIGALRM] = timer_alarm_handler
};
static void hard_handler(int sig, siginfo_t *si, void *p)
{
struct ucontext *uc = p;
mcontext_t *mc = &uc->uc_mcontext;
unsigned long pending = 1UL << sig;
do {
int nested, bail;
/*
* pending comes back with one bit set for each
* interrupt that arrived while setting up the stack,
* plus a bit for this interrupt, plus the zero bit is
* set if this is a nested interrupt.
* If bail is true, then we interrupted another
* handler setting up the stack. In this case, we
* have to return, and the upper handler will deal
* with this interrupt.
*/
bail = to_irq_stack(&pending);
if (bail)
return;
nested = pending & 1;
pending &= ~1;
while ((sig = ffs(pending)) != 0){
sig--;
pending &= ~(1 << sig);
(*handlers[sig])(sig, (struct siginfo *)si, mc);
}
/*
* Again, pending comes back with a mask of signals
* that arrived while tearing down the stack. If this
* is non-zero, we just go back, set up the stack
* again, and handle the new interrupts.
*/
if (!nested)
pending = from_irq_stack(nested);
} while (pending);
}
void set_handler(int sig)
{
struct sigaction action;
int flags = SA_SIGINFO | SA_ONSTACK;
sigset_t sig_mask;
action.sa_sigaction = hard_handler;
/* block irq ones */
sigemptyset(&action.sa_mask);
sigaddset(&action.sa_mask, SIGIO);
sigaddset(&action.sa_mask, SIGWINCH);
sigaddset(&action.sa_mask, SIGALRM);
if (sig == SIGSEGV)
flags |= SA_NODEFER;
if (sigismember(&action.sa_mask, sig))
flags |= SA_RESTART; /* if it's an irq signal */
action.sa_flags = flags;
action.sa_restorer = NULL;
if (sigaction(sig, &action, NULL) < 0)
panic("sigaction failed - errno = %d\n", errno);
sigemptyset(&sig_mask);
sigaddset(&sig_mask, sig);
if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
panic("sigprocmask failed - errno = %d\n", errno);
}
int change_sig(int signal, int on)
{
sigset_t sigset;
sigemptyset(&sigset);
sigaddset(&sigset, signal);
if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
return -errno;
return 0;
}
void block_signals(void)
{
signals_enabled = 0;
/*
* This must return with signals disabled, so this barrier
* ensures that writes are flushed out before the return.
* This might matter if gcc figures out how to inline this and
* decides to shuffle this code into the caller.
*/
barrier();
}
void unblock_signals(void)
{
int save_pending;
if (signals_enabled == 1)
return;
/*
* We loop because the IRQ handler returns with interrupts off. So,
* interrupts may have arrived and we need to re-enable them and
* recheck signals_pending.
*/
while (1) {
/*
* Save and reset save_pending after enabling signals. This
* way, signals_pending won't be changed while we're reading it.
*/
signals_enabled = 1;
/*
* Setting signals_enabled and reading signals_pending must
* happen in this order.
*/
barrier();
save_pending = signals_pending;
if (save_pending == 0)
return;
signals_pending = 0;
/*
* We have pending interrupts, so disable signals, as the
* handlers expect them off when they are called. They will
* be enabled again above.
*/
signals_enabled = 0;
/*
* Deal with SIGIO first because the alarm handler might
* schedule, leaving the pending SIGIO stranded until we come
* back here.
*
* SIGIO's handler doesn't use siginfo or mcontext,
* so they can be NULL.
*/
if (save_pending & SIGIO_MASK)
sig_handler_common(SIGIO, NULL, NULL);
/* Do not reenter the handler */
if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
timer_real_alarm_handler(NULL);
/* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
return;
}
}
int get_signals(void)
{
return signals_enabled;
}
int set_signals(int enable)
{
int ret;
if (signals_enabled == enable)
return enable;
ret = signals_enabled;
if (enable)
unblock_signals();
else block_signals();
return ret;
}
int os_is_signal_stack(void)
{
stack_t ss;
sigaltstack(NULL, &ss);
return ss.ss_flags & SS_ONSTACK;
}