linux-kernel - Re: [PATCH v2 3/8] KVM: x86: Omit VCPU_REGS_RIP from emulator's

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Message-ID: <202205311104.5D8D79E3F2@keescook>
Date:   Tue, 31 May 2022 11:04:05 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     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>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Robert Dinse <nanook@...imo.com>
Subject: Re: [PATCH v2 3/8] KVM: x86: Omit VCPU_REGS_RIP from emulator's
 _regs array

On Thu, May 26, 2022 at 09:08:12PM +0000, Sean Christopherson wrote:
> Omit RIP from the emulator's _regs array, which is used only for GPRs,
> i.e. registers that can be referenced via ModRM and/or SIB bytes.  The
> emulator uses the dedicated _eip field for RIP, and manually reads from
> _eip to handle RIP-relative addressing.
> 
> To avoid an even bigger, slightly more dangerous change, hardcode the
> number of GPRs to 16 for the time being even though 32-bit KVM's emulator
> technically should only have 8 GPRs.  Add a TODO to address that in a
> future commit.
> 
> See also the comments above the read_gpr() and write_gpr() declarations,
> and obviously the handling in writeback_registers().
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook