On Fri, Sep 24, 2021 at 12:41:32PM +0300, Kirill A. Shutemov wrote:
> On Thu, Sep 23, 2021 at 08:21:03PM +0200, Borislav Petkov wrote:
> > On Thu, Sep 23, 2021 at 12:05:58AM +0300, Kirill A. Shutemov wrote:
> > > Unless we find other way to guarantee RIP-relative access, we must use
> > > fixup_pointer() to access any global variables.
> >
> > Yah, I've asked compiler folks about any guarantees we have wrt
> > rip-relative addresses but it doesn't look good. Worst case, we'd have
> > to do the fixup_pointer() thing.
> >
> > In the meantime, Tom and I did some more poking at this and here's a
> > diff ontop.
> >
> > The direction being that we'll stick both the AMD and Intel
> > *cc_platform_has() call into cc_platform.c for which instrumentation
> > will be disabled so no issues with that.
> >
> > And that will keep all that querying all together in a single file.
>
> And still do cc_platform_has() calls in __startup_64() codepath?
>
> It's broken.
>
> Intel detection in cc_platform_has() relies on boot_cpu_data.x86_vendor
> which is not initialized until early_cpu_init() in setup_arch(). Given
> that X86_VENDOR_INTEL is 0 it leads to false-positive.
Yeah, Tom, I had the same question yesterday.
/me looks in his direction.
:-)
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
