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

[Kamal Mostafa]

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

    parisc: fix interruption handler to respect pagefault_disable()

to the linux-3.8.y-queue branch of the 3.8.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-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.12.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 0654c787529cd4be01e6c144899c47ece5cbba37 Mon Sep 17 00:00:00 2001
From: Helge Deller <deller at gmx.de>
Date: Tue, 1 Oct 2013 21:54:46 +0200
Subject: 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: Kamal Mostafa <kamal 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);
-
 	    }
 	}

--
1.8.1.2