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[4.2.y-ckt,039/268] arm64: mdscr_el1: avoid exposing DCC to userspace

Message ID 1453926929-17663-40-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa Jan. 27, 2016, 8:31 p.m. UTC 
4.2.8-ckt3 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Will Deacon <will.deacon@arm.com>

commit d8d23fa0f27f3b2942a7bbc7378c7735324ed519 upstream.

We don't want to expose the DCC to userspace, particularly as there is
a kernel console driver for it.

This patch resets mdscr_el1 to disable userspace access to the DCC
registers on the cold boot path.

Signed-off-by: Will Deacon <will.deacon@arm.com>
[ kamal: 4.2-stable prereq for
  60792ad arm64: kernel: enforce pmuserenr_el0 initialization and restore ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 arch/arm64/mm/proc.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
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Patch

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 39139a3..f28a1fe 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -156,7 +156,8 @@  ENTRY(__cpu_setup)
 
 	mov	x0, #3 << 20
 	msr	cpacr_el1, x0			// Enable FP/ASIMD
-	msr	mdscr_el1, xzr			// Reset mdscr_el1
+	mov	x0, #1 << 12			// Reset mdscr_el1 and disable
+	msr	mdscr_el1, x0			// access to the DCC from EL0
 	/*
 	 * Memory region attributes for LPAE:
 	 *