On 03/04/2016 10:12 AM, Yu-cheng Yu wrote:
> diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> index 0fbf60c..09945f1 100644
> --- a/arch/x86/kernel/fpu/signal.c
> +++ b/arch/x86/kernel/fpu/signal.c
> @@ -130,6 +130,45 @@ static inline int copy_fpregs_to_sigframe(struct
> xregs_state __user *buf)
> return err;
> }
>
> +static int may_copy_fpregs_to_sigframe(void)
> +{
> + /*
> + * In signal handling path, the kernel already checks if
> + * FPU instructions have been used before it calls
> + * copy_fpstate_to_sigframe(). We check this here again
> + * to detect any potential mis-use and saving invalid
> + * register values directly to a signal frame.
> + */
> + WARN_ONCE(!current->thread.fpu.fpstate_active,
> + "direct FPU save with no math use\n");
This is probably an OK check for this _particular_ context (since this
context is all ready to copy_to_user() the fpu state). But is it good
generally? Why couldn't you have a !fpstate_active thread that _was_
fpregs_active?
Such a thread _could_ do a direct XSAVE with no issues.
