[PATCH 3.13 127/198] powerpc/perf: Ensure all EBB register state is cleared on fork()

From: Kamal Mostafa
Date: Tue Jul 15 2014 - 18:06:59 EST -stable review patch. If anyone has any objections, please let me know.


From: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

commit 3df48c981d5a9610e02e9270b1bc4274fb536710 upstream.

In commit 330a1eb "Core EBB support for 64-bit book3s" I messed up
clear_task_ebb(). It clears some but not all of the task's Event Based
Branch (EBB) registers when we duplicate a task struct.

That allows a child task to observe the EBBHR & EBBRR of its parent,
which it should not be able to do.

Fix it by clearing EBBHR & EBBRR.

Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
arch/powerpc/include/asm/switch_to.h | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index 3b8d941..369f298 100644
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -88,6 +88,8 @@ static inline void clear_task_ebb(struct task_struct *t)
/* EBB perf events are not inherited, so clear all EBB state. */
+ t->thread.ebbrr = 0;
+ t->thread.ebbhr = 0;
t->thread.bescr = 0;
t->thread.mmcr2 = 0;
t->thread.mmcr0 = 0;

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