linux-kernel - [PATCH 4.9 17/76] powerpc/64: Use barrier

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Date:   Mon, 15 Apr 2019 20:43:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Michal Suchanek <msuchanek@...e.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 17/76] powerpc/64: Use barrier_nospec in syscall entry

commit 51973a815c6b46d7b23b68d6af371ad1c9d503ca upstream.

Our syscall entry is done in assembly so patch in an explicit
barrier_nospec.

Based on a patch by Michal Suchanek.

Signed-off-by: Michal Suchanek <msuchanek@...e.de>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/kernel/entry_64.S | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index e24ae0fa80ed..11e390662384 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -38,6 +38,7 @@
 #include <asm/context_tracking.h>
 #include <asm/tm.h>
 #include <asm/ppc-opcode.h>
+#include <asm/barrier.h>
 #include <asm/export.h>
 #ifdef CONFIG_PPC_BOOK3S
 #include <asm/exception-64s.h>
@@ -180,6 +181,15 @@ system_call:			/* label this so stack traces look sane */
 	clrldi	r8,r8,32
 15:
 	slwi	r0,r0,4
+
+	barrier_nospec_asm
+	/*
+	 * Prevent the load of the handler below (based on the user-passed
+	 * system call number) being speculatively executed until the test
+	 * against NR_syscalls and branch to .Lsyscall_enosys above has
+	 * committed.
+	 */
+
 	ldx	r12,r11,r0	/* Fetch system call handler [ptr] */
 	mtctr   r12
 	bctrl			/* Call handler */
-- 
2.19.1