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linux-next/arch/um/os-Linux/signal.c
Richard Weinberger f72c22e45e um: Make stack trace reliable against kernel mode faults
As UML uses an alternative signal stack we cannot use
the current stack pointer for stack dumping if UML itself
dies by SIGSEGV. To bypass this issue we save regs taken
from mcontext in our segv handler into thread_struct and
use these regs to obtain the stack pointer in show_stack().

Signed-off-by: Richard Weinberger <richard@nod.at>
2013-11-17 11:27:30 +01:00

315 lines
6.8 KiB
C

/*
* 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 "internal.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,
[SIGVTALRM] = 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.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 != SIGVTALRM))
unblock_signals();
(*sig_info[sig])(sig, si, &r);
errno = save_errno;
}
/*
* 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 SIGVTALRM_BIT 1
#define SIGVTALRM_MASK (1 << SIGVTALRM_BIT)
static int signals_enabled;
static unsigned int signals_pending;
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 real_alarm_handler(mcontext_t *mc)
{
struct uml_pt_regs regs;
if (mc != NULL)
get_regs_from_mc(&regs, mc);
regs.is_user = 0;
unblock_signals();
timer_handler(SIGVTALRM, NULL, &regs);
}
void alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
{
int enabled;
enabled = signals_enabled;
if (!signals_enabled) {
signals_pending |= SIGVTALRM_MASK;
return;
}
block_signals();
real_alarm_handler(mc);
set_signals(enabled);
}
void timer_init(void)
{
set_handler(SIGVTALRM);
}
void set_sigstack(void *sig_stack, int size)
{
stack_t stack = ((stack_t) { .ss_flags = 0,
.ss_sp = (__ptr_t) 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,
[SIGVTALRM] = 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, SIGVTALRM);
sigaddset(&action.sa_mask, SIGIO);
sigaddset(&action.sa_mask, SIGWINCH);
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);
if (save_pending & SIGVTALRM_MASK)
real_alarm_handler(NULL);
}
}
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;
}