linux-kernel - Re: [PATCH 1/2] KVM: x86/emulator: Defer not-present segment check in __load_segment

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Message-ID: <YgFxL1uTKPCUpokQ@google.com>
Date:   Mon, 7 Feb 2022 19:21:19 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Hou Wenlong <houwenlong.hwl@...group.com>
Cc:     kvm@...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>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Gleb Natapov <gleb@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: x86/emulator: Defer not-present segment check
 in __load_segment_descriptor()

On Thu, Jan 20, 2022, Hou Wenlong wrote:
> Per Intel's SDM on the "Instruction Set Reference", when
> loading segment descriptor, not-present segment check should
> be after all type and privilege checks. But the emulator checks
> it first, then #NP is triggered instead of #GP if privilege fails
> and segment is not present. Put not-present segment check after
> type and privilege checks in __load_segment_descriptor().

For posterity, KVM doesn't support CALL GATES or TASK GATES, so the "early" #NP
check for those is missing.

> Fixes: 38ba30ba51a00 (KVM: x86 emulator: Emulate task switch in emulator.c)
> Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@...gle.com>