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Date: Mon, 5 Jun 2023 11:31:48 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Zeng Guang <guang.zeng@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
H Peter Anvin <hpa@...or.com>, kvm@...r.kernel.org,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/6] KVM: VMX: Add new ops in kvm_x86_ops for LASS
violation check
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@...el.com>
> Tested-by: Xuelian Guo <xuelian.guo@...el.com>
> ---
> 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.
> +
> + 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)
> {
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