linux-kernel - [PATCH 3.12 067/206] x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt

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Message-Id: <03f43efc6a00eb29015222f8e9caeafdd9986a63.1416319692.git.jslaby@suse.cz>
Date:	Tue, 18 Nov 2014 15:07:02 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 067/206] x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt_disable()

From: Oleg Nesterov <oleg@...hat.com>

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

===============

commit df24fb859a4e200d9324e2974229fbb7adf00aef upstream.

Add preempt_disable() + preempt_enable() around math_state_restore() in
__restore_xstate_sig(). Otherwise __switch_to() after __thread_fpu_begin()
can overwrite fpu->state we are going to restore.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Link: http://lkml.kernel.org/r/20140902175717.GA21649@redhat.com
Reviewed-by: Suresh Siddha <sbsiddha@...il.com>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/x86/kernel/xsave.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 422fd8223470..7305625c2767 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -399,8 +399,11 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
 			set_used_math();
 		}
 
-		if (use_eager_fpu())
+		if (use_eager_fpu()) {
+			preempt_disable();
 			math_state_restore();
+			preempt_enable();
+		}
 
 		return err;
 	} else {
-- 
2.1.3

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