Messages in this thread | | | Subject | Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows correct xstates copy from kernel to user directly | From | Dave Hansen <> | Date | Fri, 29 Apr 2016 13:09:07 -0700 |
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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.
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