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

[Zhi Wang]

On Tue, 6 Jun 2023 10:57:23 +0800
Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx> wrote:

> 
> 
> On 6/5/2023 8:53 PM, Zhi Wang wrote:
> > On Mon, 5 Jun 2023 11:31:48 +0800
> > Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx> wrote:
> >
> >>
> >> On 6/1/2023 10:23 PM, Zeng Guang wrote:
> >>> Intel introduces LASS (Linear Address Separation) feature providing
> >>                         ^
> >>    missing "Space" here
> >>> 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.
> >>>
> >>> [1]A supervisor mode data access causes a LASS violation only if supervisor
> >>> mode access protection is enabled (CR4.SMAP = 1) and either RFLAGS.AC = 0
> >>> or the access implicitly accesses a system data structure.
> >>>
> >>> Following are the rules of LASS violation check on the linear address(LA).
> >>> User access to supervisor-mode address space:
> >>>       LA[bit 63] && (CPL == 3)
> >>> Supervisor access to user-mode address space:
> >>>       Instruction fetch: !LA[bit 63] && (CPL < 3)
> >>>       Data access: !LA[bit 63] && (CR4.SMAP==1) && ((RFLAGS.AC == 0 &&
> >>>                    CPL < 3) || Implicit supervisor access)
> >>>
> >>> Add new ops in kvm_x86_ops to do LASS violation check.
> >>>
> >>> Signed-off-by: Zeng Guang <guang.zeng@xxxxxxxxx>
> >>> Tested-by: Xuelian Guo <xuelian.guo@xxxxxxxxx>
> >>> ---
> >>>    arch/x86/include/asm/kvm-x86-ops.h |  3 +-
> >>>    arch/x86/include/asm/kvm_host.h    |  2 ++
> >>>    arch/x86/kvm/kvm_emulate.h         |  1 +
> >>>    arch/x86/kvm/vmx/vmx.c             | 47 ++++++++++++++++++++++++++++++
> >>>    arch/x86/kvm/vmx/vmx.h             |  2 ++
> >>>    5 files changed, 54 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> >>> index 13bc212cd4bc..8980a3bfa687 100644
> >>> --- a/arch/x86/include/asm/kvm-x86-ops.h
> >>> +++ b/arch/x86/include/asm/kvm-x86-ops.h
> >>> @@ -132,7 +132,8 @@ KVM_X86_OP_OPTIONAL(migrate_timers)
> >>>    KVM_X86_OP(msr_filter_changed)
> >>>    KVM_X86_OP(complete_emulated_msr)
> >>>    KVM_X86_OP(vcpu_deliver_sipi_vector)
> >>> -KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
> >>> +KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons)
> >>> +KVM_X86_OP_OPTIONAL_RET0(check_lass)
> >>>    
> >>>    #undef KVM_X86_OP
> >>>    #undef KVM_X86_OP_OPTIONAL
> >>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >>> index 92d8e65fe88c..98666d1e7727 100644
> >>> --- a/arch/x86/include/asm/kvm_host.h
> >>> +++ b/arch/x86/include/asm/kvm_host.h
> >>> @@ -1731,6 +1731,8 @@ struct kvm_x86_ops {
> >>>    	 * Returns vCPU specific APICv inhibit reasons
> >>>    	 */
> >>>    	unsigned long (*vcpu_get_apicv_inhibit_reasons)(struct kvm_vcpu *vcpu);
> >>> +
> >>> +	bool (*check_lass)(struct kvm_vcpu *vcpu, u64 access, u64 la, u32 flags);
> >>>    };
> >>>    
> >>>    struct kvm_x86_nested_ops {
> >>> diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
> >>> index 5b9ec610b2cb..f1439ab7c14b 100644
> >>> --- a/arch/x86/kvm/kvm_emulate.h
> >>> +++ b/arch/x86/kvm/kvm_emulate.h
> >>> @@ -91,6 +91,7 @@ struct x86_instruction_info {
> >>>    /* x86-specific emulation flags */
> >>>    #define X86EMUL_F_FETCH			BIT(0)
> >>>    #define X86EMUL_F_WRITE			BIT(1)
> >>> +#define X86EMUL_F_SKIPLASS		BIT(2)
> >>>    
> >>>    struct x86_emulate_ops {
> >>>    	void (*vm_bugged)(struct x86_emulate_ctxt *ctxt);
> >>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> >>> index a33205ded85c..876997e8448e 100644
> >>> --- a/arch/x86/kvm/vmx/vmx.c
> >>> +++ b/arch/x86/kvm/vmx/vmx.c
> >>> @@ -8130,6 +8130,51 @@ static void vmx_vm_destroy(struct kvm *kvm)
> >>>    	free_pages((unsigned long)kvm_vmx->pid_table, vmx_get_pid_table_order(kvm));
> >>>    }
> >>>    
> >>> +/*
> >>> + * 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));
> >> IMHO, it's better to skip the following checks and return false if it is
> >> out of long mode.
> >>
> > The check of long mode is in the caller implemented in in the next patch. :)
> >
> > +	if (!is_long_mode(vcpu))
> > +		return false;
> I know the callers have checked the mode, however, IMHO, it's better as 
> following:
> 
> +	if (!!(flags & X86EMUL_F_SKIPLASS) ||
> +	    !kvm_is_cr4_bit_set(vcpu, X86_CR4_LASS) || WARN_ON_ONCE(!is_long_mode(vcpu)))
> +		return false;
>
Uh. I see. LGTM. 
> 
> 
> >>> +
> >>> +	user_as = !(la >> 63);
> >> It's better to describe how LASS treat linear address in compatibility
> >> mode in changelog or/and in comment,
> >> i.e. for a linear address with only 32 bits (or 16 bits), the processor
> >> treats bit 63 as if it were 0.
> >>
> >>
> >>> +
> >>> +	/*
> >>> +	 * 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)
> >>> +		return false;
> >>> +
> >>> +	/*
> >>> +	 * Supervisor-mode _data_ accesses to user address space
> >>> +	 * cause LASS violations only if SMAP is enabled.
> >>> +	 */
> >>> +	if (!user_mode && !(access & PFERR_FETCH_MASK))
> >>> +		return kvm_is_cr4_bit_set(vcpu, X86_CR4_SMAP) && !rflags_ac;
> >>> +
> >>> +	return true;
> >>> +}
> >>> +
> >>>    static struct kvm_x86_ops vmx_x86_ops __initdata = {
> >>>    	.name = KBUILD_MODNAME,
> >>>    
> >>> @@ -8269,6 +8314,8 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
> >>>    	.complete_emulated_msr = kvm_complete_insn_gp,
> >>>    
> >>>    	.vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector,
> >>> +
> >>> +	.check_lass = vmx_check_lass,
> >>>    };
> >>>    
> >>>    static unsigned int vmx_handle_intel_pt_intr(void)
> >>> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> >>> index 9e66531861cf..f2e775b9849b 100644
> >>> --- a/arch/x86/kvm/vmx/vmx.h
> >>> +++ b/arch/x86/kvm/vmx/vmx.h
> >>> @@ -433,6 +433,8 @@ void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type);
> >>>    u64 vmx_get_l2_tsc_offset(struct kvm_vcpu *vcpu);
> >>>    u64 vmx_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu);
> >>>    
> >>> +bool vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u32 flags);
> >>> +
> >>>    static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
> >>>    					     int type, bool value)
> >>>    {
>