linux/arch/powerpc/kernel/signal.c
Michael Neuling 2b3f8e87cf powerpc/tm: Fix userspace stack corruption on signal delivery for active transactions
When in an active transaction that takes a signal, we need to be careful with
the stack.  It's possible that the stack has moved back up after the tbegin.
The obvious case here is when the tbegin is called inside a function that
returns before a tend.  In this case, the stack is part of the checkpointed
transactional memory state.  If we write over this non transactionally or in
suspend, we are in trouble because if we get a tm abort, the program counter
and stack pointer will be back at the tbegin but our in memory stack won't be
valid anymore.

To avoid this, when taking a signal in an active transaction, we need to use
the stack pointer from the checkpointed state, rather than the speculated
state.  This ensures that the signal context (written tm suspended) will be
written below the stack required for the rollback.  The transaction is aborted
becuase of the treclaim, so any memory written between the tbegin and the
signal will be rolled back anyway.

For signals taken in non-TM or suspended mode, we use the
normal/non-checkpointed stack pointer.

Tested with 64 and 32 bit signals

Signed-off-by: Michael Neuling <mikey@neuling.org>
Cc: <stable@vger.kernel.org> # v3.9
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2013-06-01 08:29:23 +10:00

214 lines
5.7 KiB
C

/*
* Common signal handling code for both 32 and 64 bits
*
* Copyright (c) 2007 Benjamin Herrenschmidt, IBM Coproration
* Extracted from signal_32.c and signal_64.c
*
* This file is subject to the terms and conditions of the GNU General
* Public License. See the file README.legal in the main directory of
* this archive for more details.
*/
#include <linux/tracehook.h>
#include <linux/signal.h>
#include <linux/uprobes.h>
#include <linux/key.h>
#include <linux/context_tracking.h>
#include <asm/hw_breakpoint.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include <asm/debug.h>
#include <asm/tm.h>
#include "signal.h"
/* Log an error when sending an unhandled signal to a process. Controlled
* through debug.exception-trace sysctl.
*/
int show_unhandled_signals = 1;
/*
* Allocate space for the signal frame
*/
void __user * get_sigframe(struct k_sigaction *ka, unsigned long sp,
size_t frame_size, int is_32)
{
unsigned long oldsp, newsp;
/* Default to using normal stack */
oldsp = get_clean_sp(sp, is_32);
/* Check for alt stack */
if ((ka->sa.sa_flags & SA_ONSTACK) &&
current->sas_ss_size && !on_sig_stack(oldsp))
oldsp = (current->sas_ss_sp + current->sas_ss_size);
/* Get aligned frame */
newsp = (oldsp - frame_size) & ~0xFUL;
/* Check access */
if (!access_ok(VERIFY_WRITE, (void __user *)newsp, oldsp - newsp))
return NULL;
return (void __user *)newsp;
}
static void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
int has_handler)
{
unsigned long ret = regs->gpr[3];
int restart = 1;
/* syscall ? */
if (TRAP(regs) != 0x0C00)
return;
/* error signalled ? */
if (!(regs->ccr & 0x10000000))
return;
switch (ret) {
case ERESTART_RESTARTBLOCK:
case ERESTARTNOHAND:
/* ERESTARTNOHAND means that the syscall should only be
* restarted if there was no handler for the signal, and since
* we only get here if there is a handler, we dont restart.
*/
restart = !has_handler;
break;
case ERESTARTSYS:
/* ERESTARTSYS means to restart the syscall if there is no
* handler or the handler was registered with SA_RESTART
*/
restart = !has_handler || (ka->sa.sa_flags & SA_RESTART) != 0;
break;
case ERESTARTNOINTR:
/* ERESTARTNOINTR means that the syscall should be
* called again after the signal handler returns.
*/
break;
default:
return;
}
if (restart) {
if (ret == ERESTART_RESTARTBLOCK)
regs->gpr[0] = __NR_restart_syscall;
else
regs->gpr[3] = regs->orig_gpr3;
regs->nip -= 4;
regs->result = 0;
} else {
regs->result = -EINTR;
regs->gpr[3] = EINTR;
regs->ccr |= 0x10000000;
}
}
static int do_signal(struct pt_regs *regs)
{
sigset_t *oldset = sigmask_to_save();
siginfo_t info;
int signr;
struct k_sigaction ka;
int ret;
int is32 = is_32bit_task();
signr = get_signal_to_deliver(&info, &ka, regs, NULL);
/* Is there any syscall restart business here ? */
check_syscall_restart(regs, &ka, signr > 0);
if (signr <= 0) {
/* No signal to deliver -- put the saved sigmask back */
restore_saved_sigmask();
regs->trap = 0;
return 0; /* no signals delivered */
}
#ifndef CONFIG_PPC_ADV_DEBUG_REGS
/*
* Reenable the DABR before delivering the signal to
* user space. The DABR will have been cleared if it
* triggered inside the kernel.
*/
if (current->thread.hw_brk.address &&
current->thread.hw_brk.type)
set_breakpoint(&current->thread.hw_brk);
#endif
/* Re-enable the breakpoints for the signal stack */
thread_change_pc(current, regs);
if (is32) {
if (ka.sa.sa_flags & SA_SIGINFO)
ret = handle_rt_signal32(signr, &ka, &info, oldset,
regs);
else
ret = handle_signal32(signr, &ka, &info, oldset,
regs);
} else {
ret = handle_rt_signal64(signr, &ka, &info, oldset, regs);
}
regs->trap = 0;
if (ret) {
signal_delivered(signr, &info, &ka, regs,
test_thread_flag(TIF_SINGLESTEP));
}
return ret;
}
void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
{
user_exit();
if (thread_info_flags & _TIF_UPROBE)
uprobe_notify_resume(regs);
if (thread_info_flags & _TIF_SIGPENDING)
do_signal(regs);
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
}
user_enter();
}
unsigned long get_tm_stackpointer(struct pt_regs *regs)
{
/* When in an active transaction that takes a signal, we need to be
* careful with the stack. It's possible that the stack has moved back
* up after the tbegin. The obvious case here is when the tbegin is
* called inside a function that returns before a tend. In this case,
* the stack is part of the checkpointed transactional memory state.
* If we write over this non transactionally or in suspend, we are in
* trouble because if we get a tm abort, the program counter and stack
* pointer will be back at the tbegin but our in memory stack won't be
* valid anymore.
*
* To avoid this, when taking a signal in an active transaction, we
* need to use the stack pointer from the checkpointed state, rather
* than the speculated state. This ensures that the signal context
* (written tm suspended) will be written below the stack required for
* the rollback. The transaction is aborted becuase of the treclaim,
* so any memory written between the tbegin and the signal will be
* rolled back anyway.
*
* For signals taken in non-TM or suspended mode, we use the
* normal/non-checkpointed stack pointer.
*/
#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
if (MSR_TM_ACTIVE(regs->msr)) {
tm_enable();
tm_reclaim(&current->thread, regs->msr, TM_CAUSE_SIGNAL);
if (MSR_TM_TRANSACTIONAL(regs->msr))
return current->thread.ckpt_regs.gpr[1];
}
#endif
return regs->gpr[1];
}