Re: [PATCH v1 3/6] KVM: VMX: Add new ops in kvm_x86_ops for LASS violation check

[Zeng Guang <guang.zeng@intel.com>]

On 6/5/2023 10:07 PM, Yuan Yao wrote:
> On Thu, Jun 01, 2023 at 10:23:06PM +0800, Zeng Guang wrote:
>> Intel introduces LASS (Linear Address Separation) feature providing
>> an independent mechanism to achieve the mode-based protection.
>>
>> LASS partitions 64-bit linear address space into two halves, user-mode
>> address (LA[bit 63]=0) and supervisor-mode address (LA[bit 63]=1). It
>> stops any code execution or conditional data access[1]
>>      1. from user mode to supervisor-mode address space
>>      2. from supervisor mode to user-mode address space
>> and generates LASS violation fault accordingly.
>>
>> +/*
>> + * Determine whether an access to the linear address causes a LASS violation.
>> + * LASS protection is only effective in long mode. As a prerequisite, caller
>> + * should make sure vCPU running in long mode and invoke this api to do LASS
>> + * violation check.
>> + */
>> +bool vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u32 flags)
>> +{
>> +	bool user_mode, user_as, rflags_ac;
>> +
>> +	if (!!(flags & X86EMUL_F_SKIPLASS) ||
>> +	    !kvm_is_cr4_bit_set(vcpu, X86_CR4_LASS))
>> +		return false;
>> +
>> +	WARN_ON_ONCE(!is_long_mode(vcpu));
>> +
>> +	user_as = !(la >> 63);
>> +
>> +	/*
>> +	 * An access is a supervisor-mode access if CPL < 3 or if it implicitly
>> +	 * accesses a system data structure. For implicit accesses to system
>> +	 * data structure, the processor acts as if RFLAGS.AC is clear.
>> +	 */
>> +	if (access & PFERR_IMPLICIT_ACCESS) {
>> +		user_mode = false;
>> +		rflags_ac = false;
>> +	} else {
>> +		user_mode = vmx_get_cpl(vcpu) == 3;
>> +		if (!user_mode)
>> +			rflags_ac = !!(kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
>> +	}
>> +
>> +	if (user_mode == user_as)
> Confused by user_as, it's role of address(U/S) so how about
> "user_addr" ? "if (user_mode == user_addr)" looks more clear
> to me.
>
Actually "as" stands for "address space". I suppose it more precise. :)