[PATCH] x86/fpu: Fix invalid FPU ptrace state after execve

[Yu-cheng Yu]

Robert O'Callahan reported that after an execve PTRACE_GETREGSET
NT_X86_XSTATE continues to return the pre-exec register values
until the exec'ed task modifies FPU state.  The test code is at
https://bugzilla.redhat.com/attachment.cgi?id=1164286.

What is happening is when eagerfpu is enabled, fpu__clear() did
not properly clear fpstate.  Fix it by doing just that.

Signed-off-by: Yu-cheng Yu <yu-cheng...@intel.com>
Reported-by: Robert O'Callahan <rob...@ocallahan.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Borislav Petkov <b...@suse.de>
Cc: David Hansen <dave.han...@linux.intel.com>
Cc: Fenghua Yu <fenghua...@intel.com>
Cc: "Ravi V. Shankar" <ravi.v.shan...@intel.com>
---
 arch/x86/kernel/fpu/core.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 4700401..4c203c4 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -521,14 +521,14 @@ void fpu__clear(struct fpu *fpu)
 {
        WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an 
anomaly */
 
-       if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) {
-               /* FPU state will be reallocated lazily at the first use. */
-               fpu__drop(fpu);
-       } else {
-               if (!fpu->fpstate_active) {
-                       fpu__activate_curr(fpu);
-                       user_fpu_begin();
-               }
+       fpu__drop(fpu);
+
+       /*
+        * When eagerfpu is used, make sure fpstate is cleared and initialized.
+        */
+       if (use_eager_fpu()) {
+               fpu__activate_curr(fpu);
+               user_fpu_begin();
                copy_init_fpstate_to_fpregs();
        }
 }
-- 
1.9.1