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SubjectRe: [PATCH 02/19] x86, fpu: Wrap get_xsave_addr() to make it safer
On 05/28/2015 01:41 AM, Ingo Molnar wrote:
>> > + union fpregs_state *xstate;
>> > +
>> > + if (!current->thread.fpu.fpstate_active)
>> > + return NULL;
>> > + /*
>> > + * fpu__save() takes the CPU's xstate registers
>> > + * and saves them off to the 'fpu memory buffer.
>> > + */
>> > + fpu__save(&current->thread.fpu);
>> > + xstate = &current->thread.fpu.state;
>> > +
>> > + return get_xsave_addr(&xstate->xsave, xsave_state);
> Small nit, this would become a lot shorter if you introduced a helper local
> variable:
>
> struct fpu *fpu = &current->thread.fpu;
>
> But more importantly, for a generic get_xsave_field_ptr() API, fpu__save() is not
> enough: fpu__save() will only save FPU registers into memory if necessary (i.e. if
> the FPU is already in use), and if you call it on a task with no FPU state then it
> will still have an !fpu->fpstate_active FPU state after the call, with random,
> invalid data in the xsave area.

But why does this matter? We just did a !fpu.fpstate_active check, so
we can't have a !fpu.fpstate_active before or after the call.


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