linux-kernel - Re: [PATCH] x86/spectre: Expand test for vulnerability to empty RSB exploits

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Message-ID: <alpine.DEB.2.21.1808201823560.1551@nanos.tec.linutronix.de>
Date:   Mon, 20 Aug 2018 18:24:50 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jim Mattson <jmattson@...gle.com>
cc:     Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        Fred Jacobs <fjacobs@...are.com>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH] x86/spectre: Expand test for vulnerability to empty RSB
 exploits

On Mon, 20 Aug 2018, Jim Mattson wrote:
> On Mon, Aug 20, 2018 at 9:00 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > On Tue, 7 Aug 2018, Jim Mattson wrote:
> >
> > > Skylake-era Intel CPUs are vulnerable to exploits of empty RSB
> > > conditions. On hardware, platform vulnerability can be determined
> > > simply by checking the processor's DisplayModel/DisplayFamily
> > > signature.  However, when running in a VM, the operating system should
> > > also query IA32_ARCH_CAPABILITIES.RSBA[bit 2], a synthetic bit that
> > > can be set by a hypervisor to indicate that the VM might run on a
> > > vulnerable physical processor, regardless of the
> > > DisplayModel/DisplayFamily reported by CPUID.
> > >
> > > Note that IA32_ARCH_CAPABILITIES.RSBA[bit 2] is always clear on
> > > hardware, so the DisplayModel/DisplayFamily check is still required.
> > >
> > > For all of the details, see the Intel white paper, "Retpoline: A
> > > Branch Target Injection Mitigation" (document number 337131-001),
> > > section 5.3: Virtual Machine CPU Identification.
> > >
> > > Signed-off-by: Jim Mattson <jmattson@...gle.com>
> > > Reviewed-by: Peter Shier <pshier@...gle.com>
> >
> > That has been superseeded by:
> >
> >   fdf82a7856b3 ("x86/speculation: Protect against userspace-userspace spectreRSB")
> >
> > right? At least it does not apply anymore...
> 
> Right. It doesn't appear that Skylake CPUs get any special treatment any more.

Yeah, it's universally f*cked up by now.

Thanks,

	tglx