Re: [PATCH] Re: SSE related security hole

Andrea Arcangeli
2002-04-24T00:33:22Z

On Tue, Apr 23, 2002 at 12:21:29PM -0700, Linus Torvalds wrote:
>
>
> On Sat, 20 Apr 2002, Andrea Arcangeli wrote:
> >
> > I mean, if they change the registers layout, and so if they require a
> > different empty FPU state, they must as well add yet another bitflag to
> > enable SSE3, if they don't the chip isn't backwards compatible.
>
> I have unofficial confirmation from Intel that the way to architecturally
> initialize the FPU state is indeed something like
>
> memset(&fxsave, 0, sizeof(struct i387_fxsave_struct));
> fxsave.cwd = 0x37f;
> fxsave.mxcsr = 0x1f80;
> fxrstor(&fxsave);
>
> and the person in question is trying to make sure this is documented so
> that we won't be bitten by this in the future.

Ok, thanks for the info. The advantage (now that it is documented! :) is
that they can add the xmm8-15 reigsters of x86-64 to x86 too without
requiring any change to linux. On the linux side we obviously don't care
if they document it retroactive as an errata of sse docs, so for us it
doesn't matter even if they don't add an additional bitflag before
adding the xmm8-15 registers. Basically they should only deal with the
other operative systems now.

Andrea