linux-kernel - Re: [PATCH v2 53/63] KVM: x86: Use struct

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Message-ID: <YR2PhlO3njPcFOkg@google.com>
Date:   Wed, 18 Aug 2021 22:53:58 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        kvm@...r.kernel.org, "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-staging@...ts.linux.dev,
        linux-block@...r.kernel.org, linux-kbuild@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 53/63] KVM: x86: Use struct_group() to zero decode
 cache

On Wed, Aug 18, 2021, Kees Cook wrote:
> On Wed, Aug 18, 2021 at 03:11:28PM +0000, Sean Christopherson wrote:
> > From dbdca1f4cd01fee418c252e54c360d518b2b1ad6 Mon Sep 17 00:00:00 2001
> > From: Sean Christopherson <seanjc@...gle.com>
> > Date: Wed, 18 Aug 2021 08:03:08 -0700
> > Subject: [PATCH] KVM: x86: Replace memset() "optimization" with normal
> >  per-field writes
> > 
> > Explicitly zero select fields in the emulator's decode cache instead of
> > zeroing the fields via a gross memset() that spans six fields.  gcc and
> > clang are both clever enough to batch the first five fields into a single
> > quadword MOV, i.e. memset() and individually zeroing generate identical
> > code.
> > 
> > Removing the wart also prepares KVM for FORTIFY_SOURCE performing
> > compile-time and run-time field bounds checking for memset().
> > 
> > No functional change intended.
> > 
> > Reported-by: Kees Cook <keescook@...omium.org>
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>
> 
> Do you want me to take this patch into my tree, or do you want to carry
> it for KVM directly?

That's a Paolo question :-)

What's the expected timeframe for landing stricter bounds checking?  If it's
5.16 or later, the easiest thing would be to squeak this into 5.15.