Messages in this thread | | | Date | Fri, 29 Apr 2016 15:43:39 -0700 | From | Yu-cheng Yu <> | Subject | Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows correct xstates copy from kernel to user directly |
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On Fri, Apr 29, 2016 at 01:09:07PM -0700, Dave Hansen wrote: > 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.
But it won't come to this function unless fpstate_active is ture?
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