[PATCH 3.8 23/81] parisc: fix interruption handler to respect pagefault_disable()

From: Kamal Mostafa
Date: Tue Oct 29 2013 - 14:10:26 EST -stable review patch. If anyone has any objections, please let me know.


From: Helge Deller <deller@xxxxxx>

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@xxxxxx>
Signed-off-by: John David Anglin <dave.anglin@xxxxxxxx>
Signed-off-by: Helge Deller <deller@xxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
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())
parisc_terminate("Kernel Fault", regs, code, fault_address);


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