Messages in this thread | | | Date | Mon, 24 Apr 2023 15:43:55 +0800 | Subject | Re: [PATCH 2/6] KVM: VMX: Add new ops in kvm_x86_ops for LASS violation check | From | Binbin Wu <> |
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On 4/20/2023 9:37 PM, Zeng Guang wrote: > Intel introduce LASS (Linear Address Separation) feature providing /s/introduce/introduces
> 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 data access > 1. from user mode to supervisor-mode address space > 2. from supervisor mode to user-mode address space > and generates LASS violation fault accordingly. IMO, the description of the point 2 may be misleading that LASS stops any data access from supervisor mode to user mode address space, although the description following adds the conditions.
> > 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 rule of LASS violation check on the linear address(LA). /s/rule/rules
> 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@intel.com> > --- > arch/x86/include/asm/kvm-x86-ops.h | 1 + > arch/x86/include/asm/kvm_host.h | 5 +++ > arch/x86/kvm/vmx/vmx.c | 55 ++++++++++++++++++++++++++++++ > arch/x86/kvm/vmx/vmx.h | 2 ++ > 4 files changed, 63 insertions(+) > > diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h > index abccd51dcfca..f76c07f2674b 100644 > --- a/arch/x86/include/asm/kvm-x86-ops.h > +++ b/arch/x86/include/asm/kvm-x86-ops.h > @@ -131,6 +131,7 @@ 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(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 8ff89a52ef66..31fb8699a1ff 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -69,6 +69,9 @@ > #define KVM_X86_NOTIFY_VMEXIT_VALID_BITS (KVM_X86_NOTIFY_VMEXIT_ENABLED | \ > KVM_X86_NOTIFY_VMEXIT_USER) > > +/* x86-specific emulation flags */ > +#define KVM_X86_EMULFLAG_SKIP_LASS _BITULL(1) Do you use the flag outside of emulator? For LAM patch, it's planned to move the flags inside emulator.
> + > /* x86-specific vcpu->requests bit members */ > #define KVM_REQ_MIGRATE_TIMER KVM_ARCH_REQ(0) > #define KVM_REQ_REPORT_TPR_ACCESS KVM_ARCH_REQ(1) > @@ -1706,6 +1709,8 @@ 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, u64 flags); The flags may be dropped if the caller knows to skip it or not.
> }; > > struct kvm_x86_nested_ops { > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index c923d7599d71..581327ede66a 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -8070,6 +8070,59 @@ 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 VM Should be 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, u64 flags) > +{ > + bool user_mode, user_as, rflags_ac; > + > + if (!!(flags & KVM_X86_EMULFLAG_SKIP_LASS) || > + !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) { > + /* > + * 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; > + } else { > + return true; > + } > + } > + > + return false; > +} > + > +static bool vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags) > +{ > + return is_long_mode(vcpu) && __vmx_check_lass(vcpu, access, la, flags); > +} > + > static struct kvm_x86_ops vmx_x86_ops __initdata = { > .name = "kvm_intel", > > @@ -8207,6 +8260,8 @@ 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 a3da84f4ea45..6569385a5978 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, u64 flags); > + > static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, > int type, bool value) > {
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