[PATCH 3.15 47/66] powerpc/perf: Ensure all EBB register state is cleared on fork()

Greg Kroah-Hartman
2014-07-04T22:17:20Z

From: Michael Ellerman <mpe@ellerman.id.au>

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@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/include/asm/switch_to.h | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -84,6 +84,8 @@ static inline void clear_task_ebb(struct
{
#ifdef CONFIG_PPC_BOOK3S_64
/* 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;