[PATCH 175/208] x86/fpu: Clean up fpu__clear() state handling

[Ingo Molnar]

We currently leak FPU state across execve() boundaries on eagerfpu systems:

	$ /host/home/mingo/dump-xmm-regs-exec
	# XMM state before execve():
	XMM0 : 000000000000dede
	XMM1 : 000000000000dedf
	XMM2 : 000000000000dee0
	XMM3 : 000000000000dee1
	XMM4 : 000000000000dee2
	XMM5 : 000000000000dee3
	XMM6 : 000000000000dee4
	XMM7 : 000000000000dee5
	XMM8 : 000000000000dee6
	XMM9 : 000000000000dee7
	XMM10: 000000000000dee8
	XMM11: 000000000000dee9
	XMM12: 000000000000deea
	XMM13: 000000000000deeb
	XMM14: 000000000000deec
	XMM15: 000000000000deed

	# XMM state after execve(), in the new task context:
	XMM0 : 0000000000000000
	XMM1 : 2f2f2f2f2f2f2f2f
	XMM2 : 0000000000000000
	XMM3 : 0000000000000000
	XMM4 : 00000000000000ff
	XMM5 : 00000000ff000000
	XMM6 : 000000000000dee4
	XMM7 : 000000000000dee5
	XMM8 : 0000000000000000
	XMM9 : 0000000000000000
	XMM10: 0000000000000000
	XMM11: 0000000000000000
	XMM12: 0000000000000000
	XMM13: 000000000000deeb
	XMM14: 000000000000deec
	XMM15: 000000000000deed

The reason is that fpu__clear() does not clear out the state properly.

Fix it.

Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/fpu/core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 45ef4e51928b..33c9a43b000e 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -348,6 +348,10 @@ void fpu__restore(void)
 }
 EXPORT_SYMBOL_GPL(fpu__restore);
 
+/*
+ * Called by sys_execve() to clear the FPU fpregs, so that FPU state
+ * of the previous binary does not leak over into the exec()ed binary:
+ */
 void fpu__clear(struct task_struct *tsk)
 {
 	struct fpu *fpu = &tsk->thread.fpu;
@@ -361,8 +365,8 @@ void fpu__clear(struct task_struct *tsk)
 		 if (!fpu->fpstate_active) {
 			fpu__activate_curr(fpu);
 			user_fpu_begin();
-			restore_init_xstate();
 		}
+		restore_init_xstate();
 	}
 }
 
-- 
2.1.0

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