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Subject[PATCH v4 2/5] KVM: X86: Expose PKS to guest
Date
Protection Keys for Supervisor Pages (PKS) is a feature that extends the
Protection Keys architecture to support thread-specific permission
restrictions on supervisor pages, which extends an existing feature
named PKU (for user-mode pages).

PKS uses IA32_PKRS MSR (PKRS) at index 0x6E1 to allow software to manage
supervisor key rights. For performance consideration, PKRS intercept
will be disabled when guest CR4.PKS=1 so that the guest can access the
PKRS without VM exits.

PKS introduces dedicated control fields in VMCS to switch PKRS, which
only does the retore part. In addition, every VM exit saves PKRS into
the guest-state area in VMCS, while VM enter won't save the host value
due to the expectation that the host won't change the MSR often. Update
the host's value in VMCS manually if the MSR has been changed by the
kernel since the last time the VMCS was run.

Existence of PKS is enumerated via CPUID.(EAX=7H,ECX=0):ECX[31]. It is
enabled by setting CR4.PKS when long mode is active. PKS is only
implemented when EPT is enabled and requires the support of VM_{ENTRY,
EXIT}_LOAD_IA32_PKRS currently.

The function get_current_pkrs() in arch/x86/mm/pkeys.c exports the
per-cpu variable pkrs_cache to avoid frequent rdmsr of PKRS.

Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
---
arch/x86/include/asm/kvm_host.h | 4 +-
arch/x86/include/asm/pkeys.h | 1 +
arch/x86/kvm/cpuid.c | 3 +-
arch/x86/kvm/vmx/capabilities.h | 6 +++
arch/x86/kvm/vmx/nested.c | 1 +
arch/x86/kvm/vmx/vmcs.h | 1 +
arch/x86/kvm/vmx/vmx.c | 89 ++++++++++++++++++++++++++++++---
arch/x86/kvm/x86.c | 8 ++-
arch/x86/kvm/x86.h | 8 +++
arch/x86/mm/pkeys.c | 6 +++
include/linux/pkeys.h | 4 ++
11 files changed, 122 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d44858b69353..c8b149d9775a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -100,7 +100,8 @@
| X86_CR4_PGE | X86_CR4_PCE | X86_CR4_OSFXSR | X86_CR4_PCIDE \
| X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE \
| X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_VMXE \
- | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP))
+ | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP \
+ | X86_CR4_PKS))

#define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)

@@ -539,6 +540,7 @@ struct kvm_vcpu_arch {
unsigned long cr8;
u32 host_pkru;
u32 pkru;
+ u32 pkrs;
u32 hflags;
u64 efer;
u64 apic_base;
diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h
index 990fe9c4787c..610c94b12dbf 100644
--- a/arch/x86/include/asm/pkeys.h
+++ b/arch/x86/include/asm/pkeys.h
@@ -142,6 +142,7 @@ u32 update_pkey_val(u32 pk_reg, int pkey, unsigned int flags);
#ifdef CONFIG_ARCH_HAS_SUPERVISOR_PKEYS
__must_check int pks_key_alloc(const char *const pkey_user, int flags);
void pks_key_free(int pkey);
+u32 get_current_pkrs(void);

void pks_mk_noaccess(int pkey);
void pks_mk_readonly(int pkey);
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 06a278b3701d..4062b83091b9 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -390,7 +390,8 @@ void kvm_set_cpu_caps(void)
F(AVX512VBMI) | F(LA57) | F(PKU) | 0 /*OSPKE*/ | F(RDPID) |
F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) |
F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) |
- F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B) | 0 /*WAITPKG*/
+ F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B) | 0 /*WAITPKG*/ |
+ 0 /*PKS*/
);
/* Set LA57 based on hardware capability. */
if (cpuid_ecx(7) & F(LA57))
diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 3a1861403d73..1cadeaaf9985 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -103,6 +103,12 @@ static inline bool cpu_has_load_perf_global_ctrl(void)
(vmcs_config.vmexit_ctrl & VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL);
}

+static inline bool cpu_has_load_ia32_pkrs(void)
+{
+ return (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PKRS) &&
+ (vmcs_config.vmexit_ctrl & VM_EXIT_LOAD_IA32_PKRS);
+}
+
static inline bool cpu_has_vmx_mpx(void)
{
return (vmcs_config.vmexit_ctrl & VM_EXIT_CLEAR_BNDCFGS) &&
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 89af692deb7e..2266d98ace6f 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -250,6 +250,7 @@ static void vmx_sync_vmcs_host_state(struct vcpu_vmx *vmx,
dest->ds_sel = src->ds_sel;
dest->es_sel = src->es_sel;
#endif
+ dest->pkrs = src->pkrs;
}

static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)
diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h
index 1472c6c376f7..b5ba6407c5e1 100644
--- a/arch/x86/kvm/vmx/vmcs.h
+++ b/arch/x86/kvm/vmx/vmcs.h
@@ -40,6 +40,7 @@ struct vmcs_host_state {
#ifdef CONFIG_X86_64
u16 ds_sel, es_sel;
#endif
+ u32 pkrs;
};

struct vmcs_controls_shadow {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 47b8357b9751..a3d95492e2b7 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -363,6 +363,8 @@ module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, 0644);
static u32 vmx_segment_access_rights(struct kvm_segment *var);
static __always_inline void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu,
u32 msr, int type);
+static __always_inline void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu,
+ u32 msr, int type);

void vmx_vmexit(void);

@@ -660,6 +662,8 @@ static bool is_valid_passthrough_msr(u32 msr)
case MSR_IA32_RTIT_ADDR0_A ... MSR_IA32_RTIT_ADDR3_B:
/* PT MSRs. These are handled in pt_update_intercept_for_msr() */
return true;
+ case MSR_IA32_PKRS:
+ return true;
}

r = possible_passthrough_msr_slot(msr) != -ENOENT;
@@ -1201,6 +1205,7 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
#endif
unsigned long fs_base, gs_base;
u16 fs_sel, gs_sel;
+ u32 host_pkrs;
int i;

vmx->req_immediate_exit = false;
@@ -1233,6 +1238,21 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
*/
host_state->ldt_sel = kvm_read_ldt();

+ /*
+ * Update the host pkrs vmcs field before vcpu runs.
+ * The setting of VM_EXIT_LOAD_IA32_PKRS can ensure
+ * kvm_cpu_cap_has(X86_FEATURE_PKS) &&
+ * guest_cpuid_has(vcpu, X86_FEATURE_PKS) &&
+ * CR4.PKS=1.
+ */
+ if (vm_exit_controls_get(vmx) & VM_EXIT_LOAD_IA32_PKRS) {
+ host_pkrs = get_current_pkrs();
+ if (unlikely(host_pkrs != host_state->pkrs)) {
+ vmcs_write64(HOST_IA32_PKRS, host_pkrs);
+ host_state->pkrs = host_pkrs;
+ }
+ }
+
#ifdef CONFIG_X86_64
savesegment(ds, host_state->ds_sel);
savesegment(es, host_state->es_sel);
@@ -1920,6 +1940,13 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
else
msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
break;
+ case MSR_IA32_PKRS:
+ if (!kvm_cpu_cap_has(X86_FEATURE_PKS) ||
+ (!msr_info->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_PKS)))
+ return 1;
+ msr_info->data = vcpu->arch.pkrs;
+ break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
@@ -2189,6 +2216,18 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
else
vmx->pt_desc.guest.addr_a[index / 2] = data;
break;
+ case MSR_IA32_PKRS:
+ if (!kvm_pkrs_valid(data))
+ return 1;
+ if (!kvm_cpu_cap_has(X86_FEATURE_PKS) ||
+ (!msr_info->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_PKS)))
+ return 1;
+ if (vcpu->arch.pkrs != data) {
+ vcpu->arch.pkrs = data;
+ vmcs_write64(GUEST_IA32_PKRS, data);
+ }
+ break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
@@ -2479,7 +2518,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
VM_EXIT_LOAD_IA32_EFER |
VM_EXIT_CLEAR_BNDCFGS |
VM_EXIT_PT_CONCEAL_PIP |
- VM_EXIT_CLEAR_IA32_RTIT_CTL;
+ VM_EXIT_CLEAR_IA32_RTIT_CTL |
+ VM_EXIT_LOAD_IA32_PKRS;
if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_EXIT_CTLS,
&_vmexit_control) < 0)
return -EIO;
@@ -2503,7 +2543,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
VM_ENTRY_LOAD_IA32_EFER |
VM_ENTRY_LOAD_BNDCFGS |
VM_ENTRY_PT_CONCEAL_PIP |
- VM_ENTRY_LOAD_IA32_RTIT_CTL;
+ VM_ENTRY_LOAD_IA32_RTIT_CTL |
+ VM_ENTRY_LOAD_IA32_PKRS;
if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_ENTRY_CTLS,
&_vmentry_control) < 0)
return -EIO;
@@ -3103,8 +3144,9 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
* is in force while we are in guest mode. Do not let guests control
* this bit, even if host CR4.MCE == 0.
*/
- unsigned long hw_cr4;
+ unsigned long hw_cr4, old_cr4;

+ old_cr4 = kvm_read_cr4(vcpu);
hw_cr4 = (cr4_read_shadow() & X86_CR4_MCE) | (cr4 & ~X86_CR4_MCE);
if (is_unrestricted_guest(vcpu))
hw_cr4 |= KVM_VM_CR4_ALWAYS_ON_UNRESTRICTED_GUEST;
@@ -3152,7 +3194,7 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
}

/*
- * SMEP/SMAP/PKU is disabled if CPU is in non-paging mode in
+ * SMEP/SMAP/PKU/PKS is disabled if CPU is in non-paging mode in
* hardware. To emulate this behavior, SMEP/SMAP/PKU needs
* to be manually disabled when guest switches to non-paging
* mode.
@@ -3160,10 +3202,29 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
* If !enable_unrestricted_guest, the CPU is always running
* with CR0.PG=1 and CR4 needs to be modified.
* If enable_unrestricted_guest, the CPU automatically
- * disables SMEP/SMAP/PKU when the guest sets CR0.PG=0.
+ * disables SMEP/SMAP/PKU/PKS when the guest sets CR0.PG=0.
*/
if (!is_paging(vcpu))
- hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE);
+ hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE |
+ X86_CR4_PKS);
+ }
+
+ if ((hw_cr4 ^ old_cr4) & X86_CR4_PKS) {
+ /* pass through PKRS to guest when CR4.PKS=1 */
+ if (guest_cpuid_has(vcpu, X86_FEATURE_PKS) && hw_cr4 & X86_CR4_PKS) {
+ vmx_disable_intercept_for_msr(vcpu, MSR_IA32_PKRS, MSR_TYPE_RW);
+ vm_entry_controls_setbit(vmx, VM_ENTRY_LOAD_IA32_PKRS);
+ vm_exit_controls_setbit(vmx, VM_EXIT_LOAD_IA32_PKRS);
+ /*
+ * Every vm exit saves guest pkrs automatically, sync vcpu->arch.pkrs
+ * to VMCS.GUEST_PKRS to avoid the pollution by host pkrs.
+ */
+ vmcs_write64(GUEST_IA32_PKRS, vcpu->arch.pkrs);
+ } else {
+ vmx_enable_intercept_for_msr(vcpu, MSR_IA32_PKRS, MSR_TYPE_RW);
+ vm_entry_controls_clearbit(vmx, VM_ENTRY_LOAD_IA32_PKRS);
+ vm_exit_controls_clearbit(vmx, VM_EXIT_LOAD_IA32_PKRS);
+ }
}

vmcs_writel(CR4_READ_SHADOW, cr4);
@@ -5841,6 +5902,8 @@ void dump_vmcs(void)
vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL));
if (vmentry_ctl & VM_ENTRY_LOAD_BNDCFGS)
pr_err("BndCfgS = 0x%016llx\n", vmcs_read64(GUEST_BNDCFGS));
+ if (vmentry_ctl & VM_ENTRY_LOAD_IA32_PKRS)
+ pr_err("PKRS = 0x%016llx\n", vmcs_read64(GUEST_IA32_PKRS));
pr_err("Interruptibility = %08x ActivityState = %08x\n",
vmcs_read32(GUEST_INTERRUPTIBILITY_INFO),
vmcs_read32(GUEST_ACTIVITY_STATE));
@@ -5876,6 +5939,8 @@ void dump_vmcs(void)
vmexit_ctl & VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL)
pr_err("PerfGlobCtl = 0x%016llx\n",
vmcs_read64(HOST_IA32_PERF_GLOBAL_CTRL));
+ if (vmexit_ctl & VM_EXIT_LOAD_IA32_PKRS)
+ pr_err("PKRS = 0x%016llx\n", vmcs_read64(HOST_IA32_PKRS));

pr_err("*** Control State ***\n");
pr_err("PinBased=%08x CPUBased=%08x SecondaryExec=%08x\n",
@@ -6776,6 +6841,10 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)

pt_guest_exit(vmx);

+ if (static_cpu_has(X86_FEATURE_PKS) &&
+ kvm_read_cr4_bits(vcpu, X86_CR4_PKS))
+ vcpu->arch.pkrs = vmcs_read64(GUEST_IA32_PKRS);
+
kvm_load_host_xsave_state(vcpu);

vmx->nested.nested_run_pending = 0;
@@ -7280,6 +7349,14 @@ static __init void vmx_set_cpu_caps(void)
if (vmx_pt_mode_is_host_guest())
kvm_cpu_cap_check_and_set(X86_FEATURE_INTEL_PT);

+ /*
+ * PKS is not yet implemented for shadow paging.
+ * If not support VM_{ENTRY, EXIT}_LOAD_IA32_PKRS,
+ * don't expose the PKS as well.
+ */
+ if (enable_ept && cpu_has_load_ia32_pkrs())
+ kvm_cpu_cap_check_and_set(X86_FEATURE_PKS);
+
if (vmx_umip_emulated())
kvm_cpu_cap_set(X86_FEATURE_UMIP);

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f5ede41bf9e6..684ef760481c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1213,7 +1213,7 @@ static const u32 msrs_to_save_all[] = {
MSR_IA32_RTIT_ADDR1_A, MSR_IA32_RTIT_ADDR1_B,
MSR_IA32_RTIT_ADDR2_A, MSR_IA32_RTIT_ADDR2_B,
MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
- MSR_IA32_UMWAIT_CONTROL,
+ MSR_IA32_UMWAIT_CONTROL, MSR_IA32_PKRS,

MSR_ARCH_PERFMON_FIXED_CTR0, MSR_ARCH_PERFMON_FIXED_CTR1,
MSR_ARCH_PERFMON_FIXED_CTR0 + 2, MSR_ARCH_PERFMON_FIXED_CTR0 + 3,
@@ -5718,6 +5718,10 @@ static void kvm_init_msr_list(void)
intel_pt_validate_hw_cap(PT_CAP_num_address_ranges) * 2)
continue;
break;
+ case MSR_IA32_PKRS:
+ if (!kvm_cpu_cap_has(X86_FEATURE_PKS))
+ continue;
+ break;
case MSR_ARCH_PERFMON_PERFCTR0 ... MSR_ARCH_PERFMON_PERFCTR0 + 17:
if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_PERFCTR0 >=
min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
@@ -10026,6 +10030,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)

vcpu->arch.ia32_xss = 0;

+ vcpu->arch.pkrs = 0;
+
kvm_x86_ops.vcpu_reset(vcpu, init_event);
}

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 3900ab0c6004..b63e32baad00 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -366,6 +366,12 @@ static inline bool kvm_dr6_valid(u64 data)
return !(data >> 32);
}

+static inline bool kvm_pkrs_valid(u64 data)
+{
+ /* bit[63,32] must be zero */
+ return !(data >> 32);
+}
+
void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
int kvm_spec_ctrl_test_value(u64 value);
@@ -398,6 +404,8 @@ bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
__reserved_bits |= X86_CR4_UMIP; \
if (!__cpu_has(__c, X86_FEATURE_VMX)) \
__reserved_bits |= X86_CR4_VMXE; \
+ if (!__cpu_has(__c, X86_FEATURE_PKS)) \
+ __reserved_bits |= X86_CR4_PKS; \
__reserved_bits; \
})

diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index 57718716cc70..8027f854c600 100644
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -390,3 +390,9 @@ void pks_key_free(int pkey)
__clear_bit(pkey, &pks_key_allocation_map);
}
EXPORT_SYMBOL_GPL(pks_key_free);
+
+u32 get_current_pkrs(void)
+{
+ return this_cpu_read(pkrs_cache);
+}
+EXPORT_SYMBOL_GPL(get_current_pkrs);
diff --git a/include/linux/pkeys.h b/include/linux/pkeys.h
index bed0e293f13b..480429020f4c 100644
--- a/include/linux/pkeys.h
+++ b/include/linux/pkeys.h
@@ -72,6 +72,10 @@ static inline void pks_mk_readwrite(int pkey)
{
pr_err("%s is not valid without PKS support\n", __func__);
}
+static inline u32 get_current_pkrs(void)
+{
+ return 0;
+}
#endif /* ! CONFIG_ARCH_HAS_SUPERVISOR_PKEYS */

#endif /* _LINUX_PKEYS_H */
--
2.17.1
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