[ 3.5.y.z extended stable ] Patch "parisc: fix interruption handler to respect" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    parisc: fix interruption handler to respect

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From eecdf5240b06daf2bc6e975f898717c14b4ea414 Mon Sep 17 00:00:00 2001
From: Helge Deller <deller at gmx.de>
Date: Tue, 1 Oct 2013 21:54:46 +0200
Subject: [PATCH] parisc: fix interruption handler to respect
 pagefault_disable()

commit 59b33f148cc08fb33cbe823fca1e34f7f023765e upstream.

Running an "echo t > /proc/sysrq-trigger" crashes the parisc kernel.  The
problem is, that in print_worker_info() we try to read the workqueue info via
the probe_kernel_read() functions which use pagefault_disable() to avoid
crashes like this:
    probe_kernel_read(&pwq, &worker->current_pwq, sizeof(pwq));
    probe_kernel_read(&wq, &pwq->wq, sizeof(wq));
    probe_kernel_read(name, wq->name, sizeof(name) - 1);

The problem here is, that the first probe_kernel_read(&pwq) might return zero
in pwq and as such the following probe_kernel_reads() try to access contents of
the page zero which is read protected and generate a kernel segfault.

With this patch we fix the interruption handler to call parisc_terminate()
directly only if pagefault_disable() was not called (in which case
preempt_count()==0).  Otherwise we hand over to the pagefault handler which
will try to look up the faulting address in the fixup tables.

Signed-off-by: Helge Deller <deller at gmx.de>
Signed-off-by: John David Anglin  <dave.anglin at bell.net>
Signed-off-by: Helge Deller <deller at gmx.de>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/parisc/kernel/traps.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
index 45ba99f..71d7d72 100644
--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -810,14 +810,14 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
 	else {

 	    /*
-	     * The kernel should never fault on its own address space.
+	     * The kernel should never fault on its own address space,
+	     * unless pagefault_disable() was called before.
 	     */

-	    if (fault_space == 0)
+	    if (fault_space == 0 && !in_atomic())
 	    {
 		pdc_chassis_send_status(PDC_CHASSIS_DIRECT_PANIC);
 		parisc_terminate("Kernel Fault", regs, code, fault_address);
-
 	    }
 	}

--
1.8.3.2