4.8-stable review patch. If anyone has any objections, please let me know.
------------------ From: Yu-cheng Yu <[email protected]> commit b22cbe404a9cc3c7949e380fa1861e31934c8978 upstream. 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: 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]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- arch/x86/kernel/fpu/core.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -517,14 +517,14 @@ void fpu__clear(struct fpu *fpu) { WARN_ON_FPU(fpu != ¤t->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(); } }
