linux-kernel - Re: [PATCH 03/22] KVM: x86: Support IBPB

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Message-ID: <ZOOV8CoKqC/71IUW@google.com>
Date:   Mon, 21 Aug 2023 16:50:56 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Nikolay Borisov <nik.borisov@...e.com>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Babu Moger <babu.moger@....com>,
        Paolo Bonzini <pbonzini@...hat.com>, David.Kaplan@....com,
        gregkh@...uxfoundation.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 03/22] KVM: x86: Support IBPB_BRTYPE and SBPB

On Mon, Aug 21, 2023, Nikolay Borisov wrote:
> 
> On 21.08.23 г. 19:35 ч., Sean Christopherson wrote:
> > On Mon, Aug 21, 2023, Josh Poimboeuf wrote:
> > +               if (!boot_cpu_has(X86_FEATURE_IBPB))
> > +                       reserved_bits |= PRED_CMD_IBPB;
> > +
> > +               if (!boot_cpu_has(X86_FEATURE_SBPB))
> > +                       reserved_bits |= PRED_CMD_SBPB;
> > -               if (!boot_cpu_has(X86_FEATURE_IBPB) || (data & ~PRED_CMD_IBPB))
> > -                       return 1;
> 
> Surely data must be sanitized against reserved_bit before this if is
> executed?

Heh, yeah, I missed that minor detail in my quick write-up.