x86/fpu: Fix invalid FPU ptrace state after execve()

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 fpu__clear() does not properly clear fpstate.
Fix it by doing just that.

Reported-by: Robert O'Callahan <[email protected]>
Signed-off-by: Yu-cheng Yu <[email protected]>
Cc: <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: David Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 47004010ad5dd42ec03e5ca075d832ef0c925e38..ebb4e95fbd741b5842b6c4a6320688f99bcf541a 100644 (file)
--- 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);
+
+       /*
+        * Make sure fpstate is cleared and initialized.
+        */
+       if (static_cpu_has(X86_FEATURE_FPU)) {
+               fpu__activate_curr(fpu);
+               user_fpu_begin();
                copy_init_fpstate_to_fpregs();
        }
 }