[PATCH 3.11 131/208] arm64: fix possible invalid FPSIMD initialization state

[Luis Henriques]

3.11.10.3 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiang Liu <jiang.liu at huawei.com>

commit 6db83cea1c975b9a102e17def7d2795814e1ae2b upstream.

If context switching happens during executing fpsimd_flush_thread(),
stale value in FPSIMD registers will be saved into current thread's
fpsimd_state by fpsimd_thread_switch(). That may cause invalid
initialization state for the new process, so disable preemption
when executing fpsimd_flush_thread().

Signed-off-by: Jiang Liu <jiang.liu at huawei.com>
Cc: Jiang Liu <liuj97 at gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Cc: Mark Brown <broonie at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arm64/kernel/fpsimd.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e8b8357..2fa308e 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -79,8 +79,10 @@ void fpsimd_thread_switch(struct task_struct *next)
 
 void fpsimd_flush_thread(void)
 {
+	preempt_disable();
 	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
 	fpsimd_load_state(&current->thread.fpsimd_state);
+	preempt_enable();
 }
 
 /*
-- 
1.8.3.2