[Bug 216033] KVM VMX nested virtualization: VMXON does not check guest CR0 against IA32_VMX_CR0_FIXED0

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=216033

--- Comment #2 from Eric Li (ercli@ucdavis.edu) ---
@Sean Christopherson Thanks for submitting the fix to this bug in
https://lore.kernel.org/lkml/20220607213604.3346000-4-seanjc@google.com/ .
However, I recently tested this fix and the behavior is not as expected.

According to Intel's SDM, VMXON may generate 2 types of exceptions:

    IF (register operand) or (CR0.PE = 0) or (CR4.VMXE = 0) or ...
        THEN #UD;
    ELSIF not in VMX operation
        THEN
            IF (CPL > 0) or (in A20M mode) or
            (the values of CR0 and CR4 are not supported in VMX operation ...
                THEN #GP(0);

For example, when CR4 value is incorrect, different exceptions may be generated
depending on which bit is incorrect. If CR4.VMXE = 0, #UD should be generated.
Otherwise, #GP(0) should be generated. However, after the fix, #UD is always
generated.

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