linux-kernel - Re: [PATCH v6 11/13] kvm, x86: update spectre-v1 mitigation

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Date:   Wed, 31 Jan 2018 09:07:10 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dan Williams <dan.j.williams@...el.com>
cc:     Ingo Molnar <mingo@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Andrew Honig <ahonig@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alan Cox <alan@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v6 11/13] kvm, x86: update spectre-v1 mitigation

On Tue, 30 Jan 2018, Dan Williams wrote:

> On Mon, Jan 29, 2018 at 5:03 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> > Commit 75f139aaf896 "KVM: x86: Add memory barrier on vmcs field lookup"
> > added a raw 'asm("lfence");' to prevent a bounds check bypass of
> > 'vmcs_field_to_offset_table'. We can save an lfence in this path and
> > just use the common array_index_nospec() helper designed for these types
> > of fixes.
> >
> > Cc: Andrew Honig <ahonig@...gle.com>
> > Cc: Jim Mattson <jmattson@...gle.com>
> > Acked-by: Paolo Bonzini <pbonzini@...hat.com>
> > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> 
> 
> Hi Thomas,
> 
> I notice this one missing from -tip, I suspect because of the
> collision with the raw 'lfence' that is in current mainline? No
> worries, I'll send a rebased fixup to Paolo directly once
> array_idx_nospec() goes upstream.

It did not apply for that reason and I'm still trying to keep x86/pti as
clean as it goes to keep GregKHs backporting hell somehow under control.

Sorry, I wanted to reply on that, but then my brain shut down after pushing
it out.

Thanks,

	tglx