Code: int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
			    unsigned long error_code)
{
	struct vm_area_struct * vma;
	struct mm_struct *mm = current->mm;
	siginfo_t info;
	int code = SEGV_MAPERR;
	int is_write = 0, ret;
	int trap = TRAP(regs);
 	int is_exec = trap == 0x400;

#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
	/*
	 * Fortunately the bit assignments in SRR1 for an instruction
	 * fault and DSISR for a data fault are mostly the same for the
	 * bits we are interested in.  But there are some bits which
	 * indicate errors in DSISR but can validly be set in SRR1.
	 */
	if (trap == 0x400)
		error_code &= 0x48200000;
	else
		is_write = error_code & DSISR_ISSTORE;
#else
	is_write = error_code & ESR_DST;
#endif /* CONFIG_4xx || CONFIG_BOOKE */

	if (notify_page_fault(regs))
		return 0;

	if (unlikely(debugger_fault_handler(regs)))
		return 0;

	/* On a kernel SLB miss we can only check for a valid exception entry */
	if (!user_mode(regs) && (address >= TASK_SIZE))
		return SIGSEGV;

#if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE) || \
			     defined(CONFIG_PPC_BOOK3S_64))
  	if (error_code & DSISR_DABRMATCH) {
		/* DABR match */
		do_dabr(regs, address, error_code);
		return 0;
	}
#endif

	if (in_atomic() || mm == NULL) {
		if (!user_mode(regs))
			return SIGSEGV;
		/* in_atomic() in user mode is really bad,
		   as is current->mm == NULL. */
		printk(KERN_EMERG "Page fault in user mode with "
		       "in_atomic() = %d mm = %p\n", in_atomic(), mm);
		printk(KERN_EMERG "NIP = %lx  MSR = %lx\n",
		       regs->nip, regs->msr);
 		die("Weird page fault", regs, SIGSEGV);
 	}
 
	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, 0, regs, address);
 
 	/* When running in the kernel we expect faults to occur only to
 	 * addresses in user space.  All other faults represent errors in the
	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
	 * erroneous fault occurring in a code path which already holds mmap_sem
	 * we will deadlock attempting to validate the fault against the
	 * address space.  Luckily the kernel only validly references user
	 * space from well defined areas of code, which are listed in the
	 * exceptions table.
	 *
	 * As the vast majority of faults will be valid we will only perform
	 * the source reference check when there is a possibility of a deadlock.
	 * Attempt to lock the address space, if we cannot we then validate the
	 * source.  If this is invalid we can skip the address space check,
	 * thus avoiding the deadlock.
	 */
	if (!down_read_trylock(&mm->mmap_sem)) {
		if (!user_mode(regs) && !search_exception_tables(regs->nip))
			goto bad_area_nosemaphore;

		down_read(&mm->mmap_sem);
	}

	vma = find_vma(mm, address);
	if (!vma)
		goto bad_area;
	if (vma->vm_start <= address)
		goto good_area;
	if (!(vma->vm_flags & VM_GROWSDOWN))
		goto bad_area;

	/*
	 * N.B. The POWER/Open ABI allows programs to access up to
	 * 288 bytes below the stack pointer.
	 * The kernel signal delivery code writes up to about 1.5kB
	 * below the stack pointer (r1) before decrementing it.
	 * The exec code can write slightly over 640kB to the stack
	 * before setting the user r1.  Thus we allow the stack to
	 * expand to 1MB without further checks.
	 */
	if (address + 0x100000 < vma->vm_end) {
		/* get user regs even if this fault is in kernel mode */
		struct pt_regs *uregs = current->thread.regs;
		if (uregs == NULL)
			goto bad_area;

		/*
		 * A user-mode access to an address a long way below
		 * the stack pointer is only valid if the instruction
		 * is one which would update the stack pointer to the
		 * address accessed if the instruction completed,
		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
		 * (or the byte, halfword, float or double forms).
		 *
		 * If we don't check this then any write to the area
		 * between the last mapped region and the stack will
		 * expand the stack rather than segfaulting.
		 */
		if (address + 2048 < uregs->gpr[1]
		    && (!user_mode(regs) || !store_updates_sp(regs)))
			goto bad_area;
	}
	if (expand_stack(vma, address))
		goto bad_area;

good_area:
	code = SEGV_ACCERR;
#if defined(CONFIG_6xx)
	if (error_code & 0x95700000)
		/* an error such as lwarx to I/O controller space,
		   address matching DABR, eciwx, etc. */
		goto bad_area;
#endif /* CONFIG_6xx */
#if defined(CONFIG_8xx)
	/* 8xx sometimes need to load a invalid/non-present TLBs.
	 * These must be invalidated separately as linux mm don't.
	 */
	if (error_code & 0x40000000) /* no translation? */
		_tlbil_va(address, 0, 0, 0);

        /* The MPC8xx seems to always set 0x80000000, which is
         * "undefined".  Of those that can be set, this is the only
         * one which seems bad.
         */
	if (error_code & 0x10000000)
                /* Guarded storage error. */
		goto bad_area;
#endif /* CONFIG_8xx */

	if (is_exec) {
#ifdef CONFIG_PPC_STD_MMU
		/* Protection fault on exec go straight to failure on
		 * Hash based MMUs as they either don't support per-page
		 * execute permission, or if they do, it's handled already
		 * at the hash level. This test would probably have to
		 * be removed if we change the way this works to make hash
		 * processors use the same I/D cache coherency mechanism
		 * as embedded.
		 */
		if (error_code & DSISR_PROTFAULT)
			goto bad_area;
#endif /* CONFIG_PPC_STD_MMU */

		/*
		 * Allow execution from readable areas if the MMU does not
		 * provide separate controls over reading and executing.
		 *
		 * Note: That code used to not be enabled for 4xx/BookE.
		 * It is now as I/D cache coherency for these is done at
		 * set_pte_at() time and I see no reason why the test
		 * below wouldn't be valid on those processors. This -may-
		 * break programs compiled with a really old ABI though.
		 */
		if (!(vma->vm_flags & VM_EXEC) &&
		    (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
		     !(vma->vm_flags & (VM_READ | VM_WRITE))))
			goto bad_area;
	/* a write */
	} else if (is_write) {
		if (!(vma->vm_flags & VM_WRITE))
			goto bad_area;
	/* a read */
	} else {
		/* protection fault */
		if (error_code & 0x08000000)
			goto bad_area;
		if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
			goto bad_area;
	}

	/*
	 * If for any reason at all we couldn't handle the fault,
	 * make sure we exit gracefully rather than endlessly redo
	 * the fault.
	 */
	ret = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
	if (unlikely(ret & VM_FAULT_ERROR)) {
		if (ret & VM_FAULT_OOM)
			goto out_of_memory;
		else if (ret & VM_FAULT_SIGBUS)
			goto do_sigbus;
		BUG();
 	}
 	if (ret & VM_FAULT_MAJOR) {
 		current->maj_flt++;
		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
 				     regs, address);
 #ifdef CONFIG_PPC_SMLPAR
 		if (firmware_has_feature(FW_FEATURE_CMO)) {
			preempt_disable();
			get_lppaca()->page_ins += (1 << PAGE_FACTOR);
			preempt_enable();
		}
 #endif
 	} else {
 		current->min_flt++;
		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
 				     regs, address);
 	}
 	up_read(&mm->mmap_sem);
	return 0;

bad_area:
	up_read(&mm->mmap_sem);

bad_area_nosemaphore:
	/* User mode accesses cause a SIGSEGV */
	if (user_mode(regs)) {
		_exception(SIGSEGV, regs, code, address);
		return 0;
	}

	if (is_exec && (error_code & DSISR_PROTFAULT)
	    && printk_ratelimit())
		printk(KERN_CRIT "kernel tried to execute NX-protected"
		       " page (%lx) - exploit attempt? (uid: %d)\n",
		       address, current_uid());

	return SIGSEGV;

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
out_of_memory:
	up_read(&mm->mmap_sem);
	if (!user_mode(regs))
		return SIGKILL;
	pagefault_out_of_memory();
	return 0;

do_sigbus:
	up_read(&mm->mmap_sem);
	if (user_mode(regs)) {
		info.si_signo = SIGBUS;
		info.si_errno = 0;
		info.si_code = BUS_ADRERR;
		info.si_addr = (void __user *)address;
		force_sig_info(SIGBUS, &info, current);
		return 0;
	}
	return SIGBUS;
}

Vulnerability Type: DoS Overflow 
CWE ID: CWE-399
Summary: The Performance Events subsystem in the Linux kernel before 3.1 does not properly handle event overflows associated with PERF_COUNT_SW_CPU_CLOCK events, which allows local users to cause a denial of service (system hang) via a crafted application.
Commit Message: perf: Remove the nmi parameter from the swevent and overflow interface

The nmi parameter indicated if we could do wakeups from the current
context, if not, we would set some state and self-IPI and let the
resulting interrupt do the wakeup.

For the various event classes:

  - hardware: nmi=0; PMI is in fact an NMI or we run irq_work_run from
    the PMI-tail (ARM etc.)
  - tracepoint: nmi=0; since tracepoint could be from NMI context.
  - software: nmi=[0,1]; some, like the schedule thing cannot
    perform wakeups, and hence need 0.

As one can see, there is very little nmi=1 usage, and the down-side of
not using it is that on some platforms some software events can have a
jiffy delay in wakeup (when arch_irq_work_raise isn't implemented).

The up-side however is that we can remove the nmi parameter and save a
bunch of conditionals in fast paths.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Michael Cree <mcree@orcon.net.nz>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Deng-Cheng Zhu <dengcheng.zhu@gmail.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Don Zickus <dzickus@redhat.com>
Link: http://lkml.kernel.org/n/tip-agjev8eu666tvknpb3iaj0fg@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>