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

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Message-ID: <CALMp9eTSNA_52tdgqeqMpBYMkPTvhGtwwWyGMwQKH3cyiS0agA@mail.gmail.com>
Date:   Mon, 20 Aug 2018 09:22:29 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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, 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.